Physics/Radiopharm 2

Question 1

Define X, A, Z, and N on an illustration of an element

Answer 1

X = element symbol
 A = mass number
o (vs. atomic mass = total mass of protons, neutrons and electrons in a single atom)
 Z = atomic number
 N = neutron number

Question 2

Name four primary forces that act on an atom.

Answer 2

o Electromagnetic force
o Weak force
o Strong force
o Gravity

Question 3

As atomic number increases why is there an excess of neutrons?

Answer 3

Neutrons/protons -> attractive residual strong nuclear force (act over very short distances)
 Protons ->repulsive Coulombic forces (act over longer distances)
 So, with ↑Z, ↑ N to counteract longer range Coulombic repulsion by protons

Question 4

Question on nucleons – what they are, what the differences are between them and what they are made of

Answer 4

Nucleons = particles making up atomic nucleus = protons and neutrons, consist of quarks bound by residual strong nuclear force, mediated by gluons

Question 5

Question on isotopes, isotomes, isobars, etc.

Answer 5

Nuclides with same:
o isotopes – proton number
o isobars – mass number
o isomers – proton and neutron number, but different energy state
o isotones – neutron number

Question 6

Define binding energy, do heavier elements have higher/lower BE, explain

Answer 6

 Binding Energy (BE) = energy released by dissociating a system into constituent parts = (Σ (masses of individual components) – (mass of bound system)) c2

 2 types of BE: atomic vs. nuclear, both ↑ with ↑A, due to ↑ constituent parts, therefore >energy released by dissociating

Question 7

For an endoergic nuclear reaction, what are the starting and threshold energies, and which of these two quantities is equivalent to the energy required to make it go? Define coulomb barrier.

Answer 7

Endoergic nuclear reaction: a reaction that requires energy to be injected in order to proceed.

 Threshold energy = minimum kinetic energy of bombarding charged particle for nuclear reaction to be energetically possible
 Starting energy = minimum kinetic energy of bombarding charged particle required to overcome the Coulomb barrier and to conserve momentum
 Minimum kinetic energy for endoergic nuclear reaction is the larger of these two

 Coulomb barrier: minimum energy to overcome repulsive electrostatic force between a bombarding charged particle and the target nucleus

Question 8

What is the relationship between energy and wavelength of a photon

Answer 8

Inverse relationship: E=hc/λ

Question 9

Question about the radioactivity of one Curie and what it initially represented, i.e. number of decays in a second for Radium-226.

Answer 9

1 Ci = 3.7 x 10^10 Bq = disintegration rate of 1 g of 226Ra

Question 10

Define gamma ray, line of stability.

Answer 10

 Gamma ray: electromagnetic radiation released from nucleus during decay

 Line of stability: (draw arrow to line of stability on graph) N:Z ratio where more stable nuclei tend to lie

Question 11

Question on types of decay for varying nuclides, i.e. proton rich or neutron rich, as well as stability of very small and very large nuclides.

Answer 11

 proton rich: β+ decay, electron capture

 neutron rich: β- decay, high Z: α decay and spontaneous fission

 small nuclides stable if N:P ~ 1
 large nuclides stable if N:P ~1.5

 very large (Z > 82) all unstable (Bi-209 (Z=83) recently (2003) found to be unstable)

Question 12

Why does the number of neutrons in the nucleus have to increase relative to atomic number in order to maintain stability in larger nuclei?

Answer 12

 Neutrons/protons -> attractive residual strong nuclear force (act over very short distances)
 Protons ->repulsive Coulombic forces (act over longer distances)
 So, with ↑Z, ↑ N to counteract longer range Coulombic repulsion by protons

Question 13

Why are atoms radioactive? What will make them stable?

Answer 13

 Elements away from line of stability (i.e., N:Z = 1 for small nuclei and N:Z = 1.5 for large nuclei) tend to decay toward line of stability to become stable

Nuclear stability is determined by the nuclear shell structure. This depends on:
o Even numbers of nucleons (protons and neutrons) are more stable, while odd nucleon numbered nuclei tend to be less stable
o The ratio of protons to neutrons, which must decrease with increasing Z; those falling out of the range of stability, or which have too many protons and neutrons overall, are unstable and undergo radioactive decay, mediated by the weak nuclear force

Question 14

describe 4 particles from nuclear transformation and what’s average energy and soft tissue penetration?

Answer 14

 γ from IT: discrete energy; highly penetrating

 e- from β- decay: Eavg ~ 1/3 Eβmax, mm-cm penetration

Neutrino: residual energy from β+ decay, essentially infinite penetration

 Antineutrino: residual energy from β- decay, essentially infinite penetration

 Auger electrons: discrete energy (BEK – 2 BEL), typically nm-μm penetration

 Characteristic X-ray: discrete energies usually <100 keV, low penetration due to low energy

Question 15

Given a beta minus decay scheme and asked to graph the energies of the beta particles and label. French: [Draw the energy distribution curve of a negatron emitted by beta minus decay. Label E-max, E-mean and both axes

Answer 15

n -> proton + electron + antineutrino

Also: AZX -> AZ+1X + antineutrino + energy

Decays to right

Question 16

What other “particle” carries away energy in Electron capture?

Answer 16

Positron

Question 17

Write the equation for positron decay for element with mass A and atomic # Z. If a particle undergoes positron decay, does it transmutate?

Answer 17

AZX -> AZ-1X + positron + neutrino + energy

Yes, transmutates
 Transmutation happens when parent radionuclide (X) and daughter product (Y) are different chemical elements.
 Transmutation: B-, EC, B+, alpha, only isomeric transition and internal conversion don’t

Question 18

what’s common between positron and EC in terms of decay and what factor favours EC?

Answer 18

 Both in low N:P ratio nuclides, results in Z-1 transmutation and are isobaric
 ↑Z favours EC

 In both positron forms a neutron, both isobaric decay with transmutation, one by the emission of positron and neutrino (positron decay), the other by capture of K-shell electron by the nucleus and subsequent X-ray or Auger emission (EC). Larger elements favour EC as the K-shell is closer to the nucleus and more easily captured.

Question 19

Two decay modes for a proton rich nucleus. What orbital process can occur after this? Emission that can accompany electron capture is?

Answer 19

 Electron capture (EC) & positron decay

 For EC, get hole in an inner electron orbital shell, results in emission of characteristic X-ray or Auger electron

Question 20

Does the emission from a proton-rich isotope lead to transmutation?

Answer 20

 Yes, EC or positron decay, resulting in Z-1

Question 21

What type of radionuclides undergo decay by β+ and electron capture? What determines which decay the radionuclide undergoes? Why do heavier atoms undergo EC?

Answer 21

 Low N:P ratio (proton rich) nuclei
 If transition energy <1.022 MeV, can only have EC; must be >1.022 MeV, for positron decay; >transition energy makes positron more likely
 ↑ Z have inner shell electrons more tightly coupled to the nucleus  ↑EC
 Beta plus decay occurs in lighter elements, electron capture occurs in heavier elements.

Question 22

What’s Auger electron? Can you have Auger electron from K shell? Why?

Answer 22

 Occurs when an inner shell vacancy filled by an outer shell electron
 Energy released enough to eject an outer shell electron, the Auger electron, but not enough to eject an inner shell electron such as from the K shell

 Hole in K shell filled by L shell electron
 Energy released ejects another L shell electron = Auger
 Eauger = K-2L
 Emitted from outer shell, result of characteristic X-ray overcoming binding energy
 KLL = k-shell absence filled by L-shell electron; energy released overcomes binding energy of another L-shell electron which is ejected as the Auger electron; any energy above this L-shell binding energy is conferred as kinetic energy

Question 23

Define Auger electron/effect, effect of Z on fluorescent yield. Can K shell electrons be ejected as Auger electrons? Why?

Answer 23

 Occurs when an inner shell vacancy filled by an outer shell electron
 Energy released enough to eject an outer shell electron, the Auger electron, but not enough to eject an inner shell electron such as from the K shell
 Fluorescent yield = probability of characteristic x-ray / probability of Auger, ↑ with Z

Question 24

Questions about internal conversion vs. auger effect and associated energies of the two processes.

Answer 24

Internal conversion Auger

Energy source: Excited/metastable nucleus vs Orbital electron transition

Origin shell: Inner vs Outer

Kinetic energy: Discrete (Eγ – BE) vs Discrete (BEhole – BEtransition – BEAuger )

Auger effect – when an outer shell electron moves in to fill a vacant inner shell electron, the energy released is transferred to an orbital electron which is then emitted instead of characteristic x-ray.

Internal conversion – nucleus decays by transferring energy to an orbital electron, which is ejected instead of the gamma ray. The conversion electrons usually originate from one of the inner shells (K or L), provided the binding energy can be overcome. The orbital vacancy is filled by an outer shell electron, accompanied by emission of characteristic x-ray or Auger electron.

Question 25

Name two differences between beta emission and internal conversion.

Answer 25

Beta vs IC

Origin of electron - Nuclear decay vs inner shell orbit
Kinetic energy - Spectrum vs discrete (Egamma - BE)
Nuclear transmutation - Yes vs No
Electric charge (+1 or -1) vs -1
Associated particle emission - neutrino/antineutrino vs none

 The important differences are that:
o In beta decay, the electron originates from the nucleus while in internal conversion it originates from an electron shell.

o Beta particles are emitted with a continuous spectrum of energies, while conversion electrons have a discrete series of energies determined by differences of gamma ray energy and orbital electron binding energies.

Question 26

Protons vs. neutrons vs. electrons

Answer 26

P vs N vs e

Composition: baryones containing quarks vs same vs leptons

Charge - +1, 0, -1
Mass - 1.007 amu vs 1.009 amu vs 0.0005 amu
Stability - Stable; unstable; stable

Question 27

What is the use of bateman equation?

Answer 27

Solution of Bateman differential equations allows calculation of daughter radionuclide activity in a decay chain given starting conditions (e.g., for generators)

A set of first-order differential equations describing the time evolution of nuclide concentrations undergoing a serial or linear decay chain (simplest scenario is parent-daughter decay); the solution allows for determination of
daughter activity given starting conditions (i.e., initial parent and daughter atom number, activity or concentration)

Question 28

repeat of secular and transient equilibrium and examples

Answer 28

 Secular equilibrium – T1/2 of parent is&raquo_space; daughter that decrease of parent activity is negligible over course of observation (>= 100x)
o Ra-226 (T1/2 = 1620 years) -> Rn-222 (4.8 days)
o Cs-137 (30 years) -> Ba-137m (2.6 min)
16
o Sn-113 (117 days) -> In-113m (100 min)

 Transient equilibrium – T1/2 of parent is longer than daughter T1/2 but not “infinite” (10-50x) FIGURE 4-8
o Mo-99 (66 hr) -> Tc-99m (6 hr)
o Y-87 (80 hr) -> Sr-87m (2.83 hr)

 No equilibrium – daughter T1/2 is longer than parent T1/2 FIGURE 4-9
o Te-131m (30 hr) -> I-131 (8 days)

Question 29

Know examples of generator pairs for both secular and transient equilibrium and their associated half lives and decay schemes

Answer 29

and decay schemes.
 Secular
o 82Sr /82Rb/82Kr: 25.4d (EC)/76s (EC/β+)
o 68Ge/68Ga/68Zn: 271d (EC)/68m (EC/β+)
o 81Rb/81mKr/81Kr : 4.6h (EC/β+)/13.1s (EC/IT)

 Transient
o 99Mo/99mTc/99Tc: 66h (β-)/6h (IT/IC)
o 87Y/87mSr/87Sr: 80h (EC/β+)/2.8h (IT)

Question 30

What is the ratio of moly and technetium at equilibrium

Answer 30

Ratio of activities, Ad(t)/Ap(t) = (Tp / Tp - Td) x B.R. = (66 / 66 - 6) x 87% = 0.957

Question 31

How long does it take to obtain ½ the maximum yield of a Tc generator

Answer 31

Numerical solution in Mathematica yields

o t½max = 4.47614 h

Question 32

Define Carrier. Define Specific activity. Calculate the carrier-free specific activity for I-131

Answer 32

 Carrier = stable isotope of the radionuclide within sample
 Specific activity = ratio of the radioisotope activity to the total mass of the element present

 Carrier-free specific activity (CFSA) radionuclide = The highest possible specific activity.
 CFSA (Bq/g) = 4.8 x 10^18/(A x T1/2)
 A= mass number, t1/2 = ½ life (days)
 Shorter t1/2, higher the specific activity
 I-131: 4.8 x 10^18 / (131x8) = 4.6 x 1015 Bq/g
 Tc-99: 4.8 x 10^18 / (99x(6/24)) = 2.5 x 10^17 Bq/g

Question 33

Specific activity of eluate after 24 hours (After 24 hours, what is the specific activity of 99m-Tc)

Answer 33

SEE NOTES

Question 34

What are the physical half life and photon energy of I-123?

Answer 34

 T1/2 = 13.2 h

 Eγ = 159 keV

Question 35

Complete the Table below regarding: I-123 vs. I-131

Answer 35

131; Reactor; β-; 8 d; Eγ = 364 keV; Eβmax = 0.61MeV
Range in soft tissue 0.4mm

I-123; Cyclotron; electron capture; 13 h; Eγ = 159 keV

Question 36

Question on radionuclides and half lives including, but not limited to, krypton-81m, I-123, Indium-111, strontium-82, cobalt-58, chromium-51 and other odd nuclides

Answer 36

81mKr - 13s
123I - 13.2h
111In - 67h 
82Sr - 25.5d
51Cr - 28d
58Co - 71d

PLUS SEE NOTES

Question 37

4 radionuclides for radioimmunotherapy. Rank in order of longest path length

Answer 37

90Y (2.3 MeV) > 131I (606 keV) > 177Lu (498 keV) > 111In (Auger)

** ALSO SEE EDMONTON REVIEW NOTES ***

Question 38

Nuclides and T½ given, mix and match: Rb-82, Ga-68, Tc-99, O-15, Kr-81m

Answer 38

 Rb-82 75s
 Ga-68 68min
 Tc-99 211,000 years
 O-15 2min
 Kr-81m 13s

Question 39

What are the 2 energies of gamma from 57Co

Answer 39

T1/2 = 271 days, decays by EC

22 3 gamma energies:
o 122 keV (86%)
o 136 keV (11%)
o 14 keV (9%)

Question 40

67Ga. What are the 4 peaks? (4 energies of 67-Ga ) Other radionuclide that decay by EC

Answer 40

 93, 185, 300, 394 keV

Other EC decay?
o I-123, I-125, Ga-67, In-111, Tl-201, Xe-127, Fe-52, Se-75, Co-57, Co-58, Cr-51
o All the positron emitters

Question 41

Order the path length for F-18, C-11, N-13, O-15 from shortest to longest

Answer 41

PET tracer (from shortest to longest path length)
F-18 (0.63 MeV) -> C-11 (0.96) -> N-13 (1.2) -> O-15 (1.7)

(Max energy)

Question 42

Why do we prefer to use mean root squared as opposed to FWHM for describing positron movement

Answer 42

 FWHM best for Gaussian functions

 Positron range distributions have long-tails and are poorly described by Gaussian functions

 Root-mean squared is better indicator of positron range effect on spatial resolution

Question 43

What are two types of reaction to produce radionuclide in reactor?

what reaction is important to keep chain reaction going in the previous question?

Answer 43

 Fission
 Neutron activation

 Fission (highly contaminated requiring meticulous methods of separation, high specific acitivity/NCA products, low yields)

Neutron capture (low specific activity, carrier added products, chemical separation not necessary unless impurities develop).

o 235U + n -> 236U*, the objective is to have each fission neutrons emitted from one fission event stimulate, on average on additional fission event. This is accomplished by moderators (Heavy water and graphite) that thermalize the ejected neutrons, and control rods (cadmium and boron) that absorb the neutrons

Question 44

Energy is released by nuclear fission to produce radionuclides. What quantity? What is the substrate of this reaction? Write the reaction in question.

Answer 44

 202.5 MeV into KE of fission products
 235U + n  236U*
 Fission of one atom of U-235 releases 202.5 MeV in kinetic energy of fission products.

Question 45

Mo-99 is produced from fission in the —— solution. What is the physical half life of Mo?

Answer 45

 Hot nitric acid is used to dissolve the target assembly (consisting of an alloy of enriched U-235 with aluminum)
 This forms a nitrate solution of uranium, molybdenum and other fission products
 This is eluted through an alumina column to trap the molybdenum

Question 46

On radionuclide production and examples of each. Name four or five

Answer 46

 Nuclear fission - 99Mo, 133Xe, 131I
 Neutron Activation - 99Mo, 131I, 90Y
 Generator - 99mTc, 82Rb, 81mKr
 Cyclotron - 18F, 11C, 15O

Question 47

How do you produce 123I? What’s the target source? Compare the direct and indirect methods. What’s the advantage of indirect method?

Answer 47

Indirect
124Xe(p,2n) 123Cs -> 123Xe -> 123I (most common)
15-30 MeV
Contaminant free; High specific activity
Gas phase extraction
123Xe is expensive

Direct 
123Te(p,n)123I (direct)
124Te(p,2n)123I (direct)
15-8 (123Te)
26-20 (124Te)
Contaminants = 124I > 125I
Mineral acid to extract

Question 48

What are the advantage of indirect methods of I-123 production?

Answer 48

 high specific activity

 less contamination by other iodine radioisotopes such as 124I and 125I

Question 49

What is the common pathway in indirect methods of I-123 production? What is the target?

Answer 49

123Xe is intermediate in all indirect methods

 Most common target: 124Xe

Question 50

What are the parts in a medical cyclotron, how does a cyclotron work?

Answer 50

Particle accelerator consisting of:
o Vacuum assembly: prevents collisional losses of charged particles
o Ion source: produces charged particles to be accelerated
o Pair of hollow dee electrodes with gap: accelerates charged particles using alternating electric current
o Magnet: confines charged particles to spiral path
o Electrostatic deflector (positive ion) or foil extractor (negative ion): alters path of charged particles toward target
o Target: contains nuclei to be irradiated to produce transmutated products

Particles from the ion source are accelerated towards one of the dees by the electrical field generated by the applied AC voltage. In the presence of the magnetic field, they follow a circular path to the opposite side of the dee. The particles are accelerated across the gap because of direction change in AC voltage. They follow an outwardly spiraling path because of gain in energy and the beam of particles is extracted and directed onto an external target.

Question 51

What are 5 advantages of self shielded cyclotrons over vault cyclotrons?

Answer 51

 Smaller space requirement (less shielding required)
 Lower cost of installation
 Less radiation to surrounding structure
 Lower cost of decommissioning
 Easier access to target and cyclotron for maintenance

Disadvantages:
o Lower energy
o More difficult to access for service

Question 52

List 4 advantages of negative ion over positive ion cyclotron designs.

Answer 52

 High beam extraction efficiency
 Requires less shielding
 Allows multiple extraction sites & therefore more than one target can be simultaneously irradiated and different radionuclides can be prepared simultaneously
 Easier to service

Question 53

Multipart question on cyclotron vs. reactor produced radionuclides

Answer 53

Cyclotron:
Costs - Decreased up front capital, increased operating costs
Line of stability - Proton rich
Charge of bombarding particle - +/-
Purity - Increased specific activity; usually carrier free
Yield - Increased activity per mass of target; decreased total quantity produced

Reactor:
Costs - increased up front capital; lower operating
Line of stability - proton rich
Charge of bombarding particle - neutral
Purity - Fission & transmutative = increased specific activity; Non-transmutative = decreased specific activity
Yield - Opposite

Question 54

Describe 2 methods of F-18 production, advantages/disadvantages and which is more common

Answer 54

Method 1: H218O (p,n)18F*(H218O)n -> anion exchange resin to reuse H2O18-> F18-

Advantages: Increased yield, no carrier added
Disadvantages: 18O expensive (not anymore); 18F- chemistry in water difficult; Cannot easily obtain F2 for electrophilic reactions

Method 2: 20Ne(d,α)18F* in passivated Ni target (NiF)

Advantages: Produces [18F]F2 for electrophilic reactions
Disadvantages: Decreased yield; usually carrier added

Question 55

Most common reaction for 18F production via electrophilic substitution and write out reaction?

What particles bombard parent? I

Minimum energy and bombard for how long?

Answer 55

a) 20Ne(d,α) 18F* in passivated Ni target (NiF)
b) Deuterons bombarding 20Ne in a Nickel housing

c)
• Exoergic reaction (releases energy), so threshold energy = 0, and minimum energy is the starting energy = 2.7 MeV (starting energy required to overcome Coulombic barrier and conserve momentum)
• Bombardment typically 2h

Question 56

Principles of generator design.

Answer 56

 decay-growth relationship between a long-lived parent and its short-lived daughter radionuclide
 chemical property of daughter must be different from parent so it can be easily separated

 Ideal generator:
o simple, gives high yield of daughter nuclide repeatedly and reproducibily
o properly shielded to minimize radiation exposure
o sturdy and compact for shipping
o eluate should be free from parent and adsorbent material
o sterile and pyrogen free

Question 57

What is the concept behind 99mTc being eluted from the Al2O3 column and not 99Mo?

Answer 57

 Mo-99 adsorbed on the alumina column in the form NH4+MoO4-
 when it undergoes beta decay, loses affinity for the column and is free to be eluted with 0.9% NaCl solution via ion exchange (a Cl- ion is exchanged for a TcO4-)

Question 58

Eluate should be ____,____ and free of _____.

Answer 58

 Clear, colorless, free of particles

Question 59

Label schematic of Mo/99mTc generator

Answer 59

Critical components
o Eluting solvent/vial
o Glass column with alumina adsorbent containing MoO42-
o Filter
o Evaculated collecting vial
o Shielding

Question 60

How many weeks after manufacture is Mo/Tc generator good? How long is the eluate good to use? Name 2 things to test the eluate for.

Answer 60

 Generator: Lantheus Technelite expires 14 days post-manufacture
 Eluate: 12h at room temperature
 Tests:
o 99Mo breakthrough <0.15 kBq/MBq at time of administration (RN purity)
o Al3+ breakthrough <10 μg/ml (chemical purity)

Question 61

How do you dispose of a molybtech generator. Give two ways.

Answer 61

 Store and decay until activity below exemption quantity, then dispose in garbage (10 half lives - 660 hours)
 Return to manufacturer or approved disposal facility

Question 62

20 cc saline into generator and only 10 cc out, ?cause and what could you do to fix it. (20 ml put into a dry generator, and 10 come out. How can this affect this next elution? How can you prevent this problem?)

Answer 62

 Most probable cause for decreased volume out is partial loss of vacuum in the vacuum vial used to draw eluant out
 Can use a second vacuum vial
 If no additional eluent can be withdrawn, consider a leak in the system (tubing, cracked column), which depending on design, may require return to manufacturer
 Also, may have excessive ingrowth with excessive Tc-99 if don’t complete elution

Question 63

How do you assess for aluminum content. Briefly describe. What is the limit?

Answer 63

 Al3+ breakthrough: <10 μg/ml (chemical purity = fraction of material in desired chemical form, whether or not all of it is in the labeled form)

 Testing methods: aurintricarboxylic acid colorimetric test paper or methyl orange

 Presence: may indicate lack of stability of column and can affect radiopharmaceutical synthesis and biodistribution
o MDP: colloid formation; increased liver uptake
o Sulfur colloid: ↑ particle size
o RBC damage causing ↑ splenic uptake
o DTPA dissociation: increased free pertechnetate

Question 64

What is radionuclide purity? How do you test for 99mTcO4- impurity?

Answer 64

 Fraction of total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical

 Assay in dose calibrator with and without shielded container to determine 99Mo activity

Question 65

Define radionuclide purity. What is the limit for Mo-99 in Eluate? Name/ Describe two methods for testing for molybdenum contamination.

Answer 65

 Fraction of total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical

 99Mo limit in administered dose (at time of administration): <0.15 kBq/MBq

 Two methods:
o Assay in dose calibrator with and without shielded container to determine 99Mo activity
o Colorimetric: phenylhydrazine added to eluate

Question 66

Question on detection / how a moly shield works in detecting molybdium in a technetium element. Second part on alternative to detecting molybdinium in the element.

Answer 66

 Moly shield absorbs low energy 140 keV photons from 99mTc, but allows most of 740 and 780 keV photons from 99Mo through

o 6mm leads allows 35% of 740 & 780 keV photons through, so x3.5 to get breakthrough value
 Alternative: colorimetric test with phenylhydrazine

Question 67

Define chemical purity, radiochemical purity, and radionuclide purity and give examples

Answer 67

Chemical purity: fraction of material in desired chemical form, whether or not all of it is in the labeled form

Impurities: Al3+, carrier I, trace metals in In labeling, Kryptofix, non-radioactive FDG

Question 68

Define radiochemical purity. List 5 possible causes of radiochemical impurities in a pharmaceutical prep.

Answer 68

 Radiochemical purity is the fraction of total radioactivity in the desired chemical form in the radiopharmaceutical. Impurities include free and hydrolyzed Tc-99m TcO4-

5 causes:
o Decomposition of the radiopharmaceutical due to the action of a solvent
o Changes in temperature or pH
o Light
o Presence of oxidizing or reducing agents
o Radiolysis

Question 69

Define Rf: “relative front” or “retention factor”

Answer 69

 Rf = ratio of distance traveled by component to distance traveled by solvent front

Retention factor, Rf, or relative front = ratio of the distance travelled by the component to the distance the solvent front has advanced from the original point of application of the test material. It is used to identify different components in a given sample.

Question 70

What is the major problem with allowing a long time between elutions. Explain why this is an issue with certain preps and give two examples. How could you overcome this. (If generator not eluted a long time, how does this affect eluate? Which two kits are particularly affected and explain why.)

Answer 70

 With a long time between elutions, have buildup of essentially stable 99Tc (carrier)

 Competes with 99mTc in kits limited stannous, i.e., limited reducing agents

 Obtain generator eluate with short in-growth time

o HMPAO & Ultratag RBC particularly effected

Question 71

What are two generators other than strontium rubidium-82 and moly-99 technetium 99m?

Answer 71

68Ge (271 days) - 68Ga (68 min)

81Rb (4.6h) - 81mKr (13s)

Question 72

5 generator parents name daughters Sn113, Ge68, Rb81, Sr82, Zn62

Answer 72

o 99Mo – 99mTc; 99Mo has t1/2 66 hr & decays by β- to 99mTc (87%) & 99Tc
o 113Sn – 113mIn; 113Sn has t1/2 115 days & decays by e capture to 113mIn
o 68Ge – 68Ga; 68Ge has t1/2 271 days & decays by e capture to 68Ga
o 82Sr – 82Rb; 82Sr has t1/2 25 days & decays by e capture to 82Rb
o 81Rb – 81mKr; 81Rb has t1/2 4.5 hr & decays to 81mKr
o 62Zn – 62Cu; 62Zn has t1/2 9.2 hr & decays by e capture to 62Cu
o Yttrium-87 – Strontium-87m
o Tellurium-132 – Iodine-132

Question 73

Describe 2 generator systems commonly used for PET imaging currently in 2009, list half lives

Answer 73

o 82Sr/82Rb; 25 days/75 s

o 68Ge/68Ga; 271 days/68 min

Question 74

Four methods of radiopharmaceutical labeling and give an example of each

Answer 74

Isotope Exchange - I-131-MIBG

Introduction of a Foreign Label - Tc-99m compounds; In-111 labeled cells

Bifunctional Chelates - In-111 DTPA albumin; Tc-99m antibody

Biosynthesis - Co-57 B12;

Recoil labeling - Iodinated compounds

Excitation labeling - 123I-labeled compounds (from 123Xe decay)

Question 75

Define and give two examples of each:

a) Fillers
b) Antioxidants
c) Reductants
d) Catalysts

Answer 75

A) Filler:
Used to achieve rapid solubilization & stable particle size during lyophilization, also gives radiopharmaceutical some bulk to make visible in vial
 Mannitol (sestamibi kit)
NaCl (HMPAO kit)

B) Antioxidant:
o Prevents consumption of the reducing agent
 Ascorbic acid
 P-aminobenzoic acid (PABA)

C) Reductants
Reduces the TcO4 to a lower oxidation state, to make it more reactive
 Tin: SnCl2, Sn-pyrophosphate, Sn-citrate, Sn-gluconate
 Non-tin reducing agents (NaBH4 – sodium borohydride, HCl (hydrochloric acid), FeSO4)

D) Catalysts
Used to maximize reaction yield, but are not part of the final product
 Kryptofix in FDG
 Tartrate (MAG3 kit)
 Citrate (MIBI kit)

Question 76

What is the purpose of a buffer?

Answer 76

 A buffer is used to dampen the change in pH following the addition of an acid or a base
 It maintains the stability of the pH of the preparation
 Examples: Na-citrate, Na-carbonate

Question 77

Define “transchelation”. Name 2 tracers which are labeled by this method.

Answer 77

 Transchelation = ligand exchange method
o Involves first forming a 99mTc-complex with a weak ligand in aqueous media and then allowing the complex to react with a second slowly reacting ligand that is relatively more stable

Tracers:
o 99mTc-MAG3 (through 99mTc-tartrate or 99mTc-gluconate)
42
o 99mTc-ECD (through EDTA)
o 99mTc-MIBI (through citrate)

Question 78

Define chelation.

Answer 78

 Chelation = The formation of coordinate covalent bonds between two or more separate binding sites within the same ligand and a single central atom

 Examples:
o Tc-99m DTPA
o Tc-99m glucoheptonate

Question 79

What is a bifunctional chelating agent?

Answer 79

 Molecule that is conjugated to a macromolecule on one side and chelates a metal ion on the other
 Modification of the functional group alters the biodistribution

Question 80

What is a ligand?

Answer 80

 Ligands possess an unshared pair of electrons that can be donated to a metal ion to form a complex

Question 81

What is the most stable oxidation state of Tc and What is the most common tracer in this state?

Answer 81

 7+ oxidation state

 TcO4- (also Tc-SC)

Question 82

What are oxidation states of MIBI, DTPA, and pertechnetate?

Answer 82

 Sestamibi 1+
 DTPA 4+
 Tc-99m TcO4- 7+

Question 83

Oxidation state of SC, DTPA, MIBI?

Answer 83

 7+; Pertecnetate and colloid
 5+; citrate, gluconate, gluceptate, EDTA, MAG3, HSA, tetrofosmin, HMPAO
 4+; HEDP (mixture of 3+ acid, 5+ basic, 4+ neutral), EDTA and DTPA (alkaline and neutral)
 3+; DTPA and EDTA (acidic), DMSA, diphosphonates
 1+; MIBI (1+) Coordination number of 6 net charge 1+

Question 84

Which radiopharmaceuticals require heating?

Answer 84

1. MIBI
2. MAA
3. SC
4. ECD
5. MAG-3
6. Heat damaged RBCs
7. Technegas
8. Teboroxime
9. I123/I131 MIBG
10. 111IN-DTPA
11. FDG
12. FLT
13. I-131 Hippuran

Question 85

What’s the limit of maximum size of MAA particles?

Answer 85

Maximum size is 150 μm

Question 86

What component you have to add to make MAA besides reducing agent and buffer?

Answer 86

Human serum albumin

Question 87

110 particles in 1x1 mm square on hemocytometer, how many particles / ml of MAA?

Answer 87

110 particles in 1 mm2, hemocytometers have a depth of 0.1 mm

therefore there are 110 particles in 0.1 mm3 or 0.1 μl, 1100 in 1 μl. There are 1000 μl per ml, therefor there are 1,100,000 particles/ml.

Question 88

There was a question on differences between pertechnegas and technegas production.

Answer 88

Pertechnegas:
Production - >0.5% oxygen
Particle properties -> micro-aerosols of Tc oxides
Transit -> Rapid alveolar-capillary transit
Biological half life -> Short in lungs; behaves like TcO4

Technegas
Production - > pure argon atmosphere (< 0.1% oxygen)
Particle properties -> graphite enscapulated microparticles
Transit -> No significant alveolar-capillary transit
Biological half life -> Essentially infinite

Both formed by combusion of pertechnetate in furnace

Question 89

Describe the method of pertechnegas production. How long until it must be used. What will happen if you wait longer. What should you check if there is thyroid/stomach uptake (2 things). (Technegas: 1) How made; 2) how long is dose good for prior to use; 3) what happens to a dose held too long?; 4) If thyroid and blood pool seen post pertechnegas, what TWO things to check?)

Answer 89

 Load crucible with Tc-99m generator eluent (400-900 MBq in 0.14 ml normal saline)
 To make Pertechnegas, require >0.5% oxygen

 How long until it must be used
o For Technegas, as soon as possible, and certainly within the 10 minutes allowed
o For Pertechnegas, uncertain, but probably also <10 min

 What will happen if you wait longer
o For Technegas, get aggregation into larger particles and migration to walls of the chamber
o In contact with water vapour, Technetium oxides in Pertechnegas hydrolise back to pertechnetate
 What should you check if there is thyroid/stomach uptake (2 things)
o Impurity of Argon gas (99.99%) and introduction of oxygen
o Make sure correct eluate and have not over-filled crucible

Question 90

Name 2 contents of DTPA kit. Once Tc04 added, what are the relative proportions of these 3. Why is this important?

Answer 90

 DTPA and stannous chloride

 10^5-10^8 mol DTPA:10^3-10^6 mol Sn2+ : 1 mol 99mTc
o Need enough Sn2+ to reduce all 99mTc
o Need greater amount of chelate to drive chemical equilibrium to form chelated complexes, and prevent Sn and Tc colloid formation

Question 91

In kit preps, why is it important to keep O2 out of your vial.

Answer 91

 O2 oxidizes Sn2+ (less Sn2+ available to reduce Tc) -> increases free pertechnetate

 Increases radiolysis -> leads to free radicals that in turn produce free Tc99m-O4

Question 92

What solvent to use for evaluating radionuclidic purity of In-111-DPTA-pentreotide

Answer 92

 Methanol to elute product

 Water to elute free In3+

Question 93

Regarding WBC labelling, what needs to be in acidic environment and what pH?

Answer 93

 111In-chloride (pH 5 in acetate buffer) to avoid In hydroxide formation

Question 94

What are the uses of thiosulfate, gelatin, EDTA in SC kit?

Answer 94

 Thiosulfate: source of S

 Gelatin: maintains zeta-potential preventing aggregation

 EDTA: chelates cations (e.g., Al3+) to prevent flocculation

Question 95

Question on the size of filter to use for sulphur colloid in melanoma lymphoscintigraphy

Answer 95

0.1-0.2 μm

Question 96

Question on particle sizes for various colloids or uses of colloids in clinical nuclear medicine. Particle size for lymphoscintigraphy, particle size for lung scan and particle size for sulphur colloid study.


Answer 96

 Lymphoscintigraphy (filtered SC): 0.1-0.2 um

 Sulfur colloid study: 0.1-1 μm

 Lung scan/MAA: 10-100 μm

Technegas - 0.05-0.15 um

Question 97

Name 3 biological tests performed on radiopharmaceuticals.

Answer 97

1. Sterility: absence of any viable bacteria or microorganism
2. Apyrogenicity: USP Rabbit test, limulus amebocyte lysate (LAL) test
3. Toxicity

Question 98

How do you ensure sterility of radiopharmaceuticals?

Answer 98

 Use sterile technique in preparation
 Filter sterilize
 Autoclave heat stable radiopharmaceuticals

Question 99

Define pyrogenicity and two tests that are used to test for this. What is the most common cause of pyrogenicity in nuclear medicine radiopharmaceuticals?

Answer 99

 Pyrogenicity: ability of substance to induce fever
 Rabbit test and limulus amebocyte lysate test
 Most common: bacterial endotoxins

 rabbit test - inject 3 rabbits, if 1 temp increases > 0.6 degrees or total > 1.4 degrees then inject 5 more; if more than 3 greater than 0.6 degrees or total > 2.6 then the test is positive

Question 100

How do you interpret the first part of the USP rabbit test for pyrogenicity.

Answer 100

First test:

o 3 mature normal rabbits weighing ≥ 1.5 kg are kept in a room with uniform temperature.
o A test sample is injected into the ear vein of each rabbit. The volume of the test sample must be an equivalent human dosage, on a weight basis, and often 3-10 times the human dosage by volume.
o The rectal temperature of each rabbit is measured at 1, 2 and 3 hours after injection.
o If the rise in temperature of each individual animal is less than 0.6oC AND if the sum of the temperature rises in all three animals does not exceed 1.4oC then the test sample is apyrogenic.

Second test:
 Second test (if first test abnormal):
o Repeat initial study with 5 more mature normal rabbits.

o If not more than 3 of the total of 8 rabbits show a temperature rise of 0.6oC or more individually and if the sum or the individual temperature rises does not exceed 3.7oC, the material is considered to be pyrogen free.

Question 101

What is a pyrogen? Modern method for detecting pyrogens, advantages over rabbit test. (What is the current standard test? Why is this preferred over the rabbit rest? Three reasons

Answer 101

 Pyrogen: substance that can induce a fever when injected (i.e., systemic inflammatory response)

 Limulus amebocyte lysate test
o No live animal testing
o Rapid result (1 hour)
o Less radiopharmaceutical needed

Question 102

Describe 2 ways to sterilize a radiopharmaceutical

Answer 102

 Autoclave
 Filter sterilize (0.2 μm filter)
 Irradiation

Question 103

Kits with highest incidence of adverse reactions.

Answer 103

 Historically: Tc-99m albumin microspheres
 Current kit: highest is Tc-99m sulfur colloid (25%)
 MDP (10%)
 Also HIDA

Question 104

Reaction involved in most common method of FDG production. What is the typical yield? What is the minimal radiochemical purity allowed?

Answer 104

 Nucleophilic substitution in acetonitrile with Kryptofix as a phase transfer catalyst
 Mannose triflate in acetonitrile added to Kryptofix 2.2.218F-
 Acid hydrolyzed to 18F-FDG

 Typical yield: 60%
 Minimum radiochemical purity: 90%

Question 105

Most common production method of 18 FDG and what is its’ target? French: [36. What is the minimum energy required for F-18 production?

Answer 105

 18O(p,n)18F

 Target: 18O-H2O (minimum energy 2.6 MeV)

Question 106

a) How do you produce 18F?
b) What is the FDG yield?
c) How do you check F-18 FDG for radiochemical purity?
d) What limit is allowed for radiochemical purity?

Answer 106

 18O(p,n)18F (heavy water target, 10-18 MeV proton bombardment)
o 18F recovered as 18F-NaF by passing the irradiated water through anion exchange resin (QMA) column
o 18F- retained on column, eluted with potassium carbonate and Kryptofix 2.2.2 in acetonitrile

 Nucleophilic substitution in acetonitrile with Kryptofix as a phase transfer catalyst (85°C 5 min)
o Mannose triflate in acetonitrile added to Kryptofix 2.2.218F-, with K2CO3
o 18F- attacks #2 C position on mannopyranose ring, displacing highly electronegative triflate group

Then acid or base hydrolysis
 Acid or base hydrolyzed to 18F-FDG by removing acetyl protecting groups

 Typical yield: 60%
 Preparation time: 50 min
 Final solution is filtered through 0.2 μm filter and diluted with saline as needed
 Minimum radiochemical purity: 90%

 QC
o Visual inspection
 Clear, colorless solution free of particles, pH (4.5-7.5) – test with pH paper
o Specific activity >1 Ci/μmol (no special test, as 18F is carrier free)

o Radionuclide purity
 Must be >99.5%
 Use dose calibrator and do decay analysis
 Acceptable t ½ = 109.7 min (105-155)
 Or by gamma ray spectroscopy

o Radiochemical purity
 Use silica gel 60 TLC plates developed in acetonitrile/water (95:5)
 Must be >90%
 18F-FDG (Rf=0.4)
 18F-F- (Rf=0.1)
 18F-FDG non-hydrolyzed intermediate (Rf=0.6)

o Chemical purity
 Kryptofix 2.2.2: use color spot test that takes 5 min using pretreated strips of plastic based silica gel. Limit <50 μg/ml of sample volume
 Acetonitrile, ethanol and 2-chloro-2-deoxy-D-glucose can be determined by gas chromatography

OR:

 F-18 is produced by irradiation of O-18 water with protons in a cyclotron and recovered as F-18 sodium fluoride by passing the irradiated water target mixture through a carbonate type anion exchange resin column. Water passes through, but F18-(-) is retained on the column.
 O-18(p,n) F-18 reaction
 Yield is 6.5 Ci, <1.0 Ci for the Ne method.
 Deoxyglucose is labeled with F-18 by nucleophilic displacement reaction of an acetylated sugar derivative (mannose triflate) followed by hydrolysis. The yield can be as high as 60%. This is highly dependant on the kit used.

Question 107

List 2 FDG chemical impurities (worded as 2 NON radioactive contamination)

Answer 107

 Acetonitrile
 Kryptofix 2.2.2
 FDG

 Chemical purity:
o Kryptofix 2.2.2: use color spot test that takes 5 min using pretreated strips of plastic based silica gel. Limit is < 50 μg/ml of sample volume.
o Acetonitrile, ethanol and 2-chloro-2-deoxy-D-glucose can be determined by gas chromatography

Question 108

What is the effect of radioactive decay on chemical reactions

Answer 108

Radionuclide-related
o Transmutation of radionuclide in decay alters chemistry
o Long-lived isomeric decay daughter may compete for labeling (e.g., Tc-99)
o High energy recoil or daughter radionuclides can participate in labeling reactions

Radiation-related
o Radiolysis may be:
 Direct with high LET radiation like alpha paraticles, causing e.g., degradation of kit constituents
 Indirect with low LET radiation, causing free radical production, that can interfere with labeling
o Autoradiolysis or indirect radiolysis can disrupt product as well

Question 109

Methods of Radioiodination

Answer 109

o Triiodide method
o Iodine monochloride method
o Chloramine-T method
o Electrolytic method
o Enzymatic method
o Conjugation method
o Demetallation method
o Iodogen method
o Iodo-bead method

Question 110

What is the dominant interaction of energy with matter at nuclear medicine energies?

Answer 110

 For photons cross-over energy between photoelectric and Compton interactions are:

o Soft tissue/water: 20-30 keV
o NaI(Tl): 200-300 keV
o Pb: ~500 keV

Therefore, at Nuc Med energies of 100-200 keV, Compton dominates in soft tissues; photoelectric for NaI scintillators; photoelectric with high Z materials like Pb

Question 111

Describe photelectric effect

Answer 111

Atom absorbs all energy of incident photon and an orbital electron is ejected. This electron is called photoelectron and KE = E(incident photon) – BE of photoelectron

Question 112

Describe Compton scattering

Answer 112

Incident photon has much higher E than BE of electron it collides with so photon loses part of energy and is deflected through a scattering angle. Part of E is transferred to the recoil electron

 E (scatter photon) = E0 / [1 + (E0/0.511) (1-cos Ѳ)], max when Ѳ = 0
 E (recoil electron) = E0 – E (scatter photon), max when Ѳ = 180

Question 113

Describe pair production

Answer 113

a photon interacts with the electric field of a charged particle, producing a positive-negative electron pair and the photon disappears.
 KE of the electron pair = K0 – 1.022 MeV

Question 114

Describe Coherent (Rayleigh) scattering

Answer 114

photon is deflected with essentially no loss of energy. Only important at relatively low energies (<= 50 keV)

Question 115

At what angle of Compton scatter would the scattered photons be within 20% symmetric window?

Answer 115

 Eγs = Eγ / (1 + (Eγ/511 keV) (1 - cos θ))
 For Eγ = 140 keV photon, scattered photons are lower energy, so assuming 10% reduction in energy, Eγs = 140 – (10% x 140) = 126 keV yields 53.5°

Question 116

Does the increase of the interaction media’s atomic number, Z, affect energy of Compton scatter photon?

Answer 116

 No, Z does not affect Eγs
 Eγs = Eγ / (1 + (Eγ/511 keV) (1 - cos θ))

 No, Compton involves outer shell electrons
 Generally independent of Z, proportional to 1/E

Question 117

A small chart on the three mechanisms of question #30 with secondary photon and secondary electron, and you were to fill in the boxes for all three.

Answer 117

Photoelectric:
Secondary photon = characteristic xray
Secondary electron = photoelectrons (inner shell); Auger electron

Compton scattering
Secondary photon = Scattered photon (outer shell)
Secondary electron = recoil electron

Pair production
Secondary photon = annihilation photons
Secondary electron = positive/negative electron pair

Question 118

What is minimum energy for pair production?

Answer 118

1.022 MeV

Question 119

Describe 3 common interactions in NaI detector crystal

Answer 119

 Photoelectric effect <250 keV
 Compton >250 keV
 Pair production >1.022 MeV

Question 120

There is increased ionization density of charged particle at the end it track length. What is it called?

Answer 120

Bragg peak

Question 121

Question on fluorescent iodes and what affects it.

Answer 121

o Fluorescent yield is the probability that the transition of an orbital electron from an outer shell into an inner shell vacancy will yield characteristic x-rays instead of Auger electrons.

o Fluorescent yield increases with increasing Z. In other words, heavy elements have a higher fluorescent yield because they are more likely to emit x-rays

Question 122

Bremstrahlung: define. How can you shield most effectively?

Answer 122

 Electromagnetic radiation produced by deceleration or altering direction of charged particles

 Use low Z material to slow charged particles with minimal Brehmstrahlung production

Question 123

Particulate radiation versus electromagnetic radiation - their differences and interactions with matter and give two examples.

Answer 123

Particulate interactions – (collisional) ionization, excitation (radiative) bremsstrahlung

EM interactions - photoelectric, Compton scatter, pair production, rayleigh coherent scatter.

Question 124

Photon vs particulate radiation

Answer 124

Photon
Mass = 0
Charge = 0
Velocity = c
Ionization = indirectly ionizing
Interactions = photoelectric, etc...

Particulate radiation 
Mass = +
Charge = possible
Velocity = < c
Ionization = directly ionizing 
Interactions 
-> if charged particle: Collisional losses (ionization, excitation); Bremsstrahlung 
-> if neutral particles: elastic and non-elastic collisions

Question 125

Name three interactions of particulate radiation with matter.

Answer 125

 Ionization (collisional)
 Excitation (collisional)
 Bremsstrahlung (radiative)

Question 126

Question on what type of ionization neutrons perform in matter. Second part of the question was what are the effects of indirect ionization? (Another recall: How does neutron react with matter?

Answer 126

 Neutrons are indirectly ionizing, losing energy by collisions that produce secondary electrons (which in turn directly ionize)
 When sufficiently slowed, can be captured (neutron activation)

Question 127

Describe what happens with charged particle and matter “collision”?

Answer 127

 Collision can result in ionization (when orbital electron is lost) or excitation (when an atom enters excited state)

Collisional interactions include ionization and excitation; charged particle passes close enough to exert an electrical force on the orbital electrons, if the force is strong enough the orbital electron will be removed and an ionization occurs, if not then excitation may occur and the energy can be dissipated in a number of ways (atomic emissions of IR, UV, visible radiation etc.)

Question 128

what is delta ray?

Answer 128

 An ejected electron that is energetic enough to cause secondary ionizations on its own.

Question 129

Define Bragg Peak, Cerenkov Effect and LET

Answer 129

Bragg Peak – increase in ionization density from a charged particle near the end of its track length

Cerenkov effect – electromagnetic radiation emitted when a charged particle travels faster than the speed of light in a medium

Linear energy transfer (LET) – rate of energy transferred per unit track length

Question 130

Define the inverse Square Law. If you triple the distance, the exposure is reduced by?

Answer 130

Inverse square law = as distance increases, the flux of radiation decreases as 1/r^2
 So triple the distance, 1/9 the exposure

Question 131

HVL for Tc-99m, Ga-67, Co-60 (another recall: HVL in lead)

Answer 131

 99mTc: 0.03 cm
 67Ga: 0.07 cm
 60Co: 1.6 cm

HVL in lead:
 1 mm tenth value layer for Tc-99m

Question 132

What is soft tissue penetration for F-18 and C-11?

Answer 132

Maximum positron range: 18F 2 mm, 11C 4 mm

Question 133

Three types of gas filled detectors.

Answer 133

 Dose calibrator
 Geiger-Muller counter
 Survey meter

Question 134

Name two ionization chambers used clinically

Answer 134

 Dose calibrator
 Geiger-Muller counter

Ionization chambers are quite inefficient for detection of x- and gamma- rays. Only < 1% actually interact with and cause ionization of gas molecules

Question 135

Ionization chamber vs GM counter?? (isn’t GM counter an ionization chamber?

Answer 135

Ionization chamber: 
Voltage - 50-300
Discriminate individual events - N
Energy discrimination - N
Efficiency for detection of
γ & x-rays - Poor
Measure - Exposure rate (mR/hr or Gy/hr)
Quenching - N
Amplification - N

GM counter:
Voltage - 800-1000
Discriminate individual events - Y
Energy discrimination - N
Efficiency for detection of
γ & x-rays - Poor but better by factor of 10
Measure - Exposure rate (mR/hr)
Quenching - Y
Amplification - Y

GM more sensitive than ionization chamber types because they respond to individual ionizing radiation events
o display event counting rates (cpm)

Question 136

Quality control of dose calibrator including testing frequency and deviation limit

Answer 136

o Constancy: The activity of a known amount of a long lived source should be checked daily and the measured value and decay corrected calculated value should not vary by >10%

o Linearity: ensures that the dose calibrator can indicate the correct activity over the range of use between 10 mCi to the highest dose that will be administered. Performed on installation and quarterly. Values should not deviate more than 10%

o Accuracy: The activity of a known amount of a calibrated source is measured and the measured value should be within 10% of the calibrated value. Performed on installation and yearly

o Geometry Dependence: ensures that the indicated activity does not change with volume or configuration. Usually perfomed by the manufacturer.

Question 137

Name 2 ways to check dose calibrator linearity

Answer 137

1. Decay method (large dose of 99mTc measure decay every 6 hours over 72 hours, point on the graph that deviated most from the line <10%)
2. Sheilding method (series of lead shield, various thickness, apply correction and average, the result that deviates the most must deviate <10%)

Question 138

3 Daily QC on Survey Meter

Answer 138

 Battery check
 Background
 Constancy

performed daily to assess the sensitivity and consistency of the meter.

 Probe is placed directly over a sealed source (eg. 226Ra or 137Cs) to measure the exposure. This exposure reading is compared with the annual calibrated source reading (should be within 10%).

Question 139

Draw schematic of Geiger-Muller counter, describing function

Answer 139

 High sensitivity counting-type ionizing radiation detector
 Ionizations in gas chamber (argon + quenching gas) result in avalanches due to high voltage operation (accelerated electrons excited gas molecules UV photonsmore ionizations)

Question 140

Label the parts of a GM counter

Answer 140

 Input window
 Gas/ionization chamber with cathode and anode
o Fill gas: argon + quenching gas
 High voltage source
 Counting circuitry

SEE NOTES

Question 141

Characteristics of “quenching gas”

Answer 141

 Ionized quenching gas can recombine with electrons without giving off UV radiation (by dissociating into molecular fragments)
 Absorb UV radiation inhibiting further ionization
 Electron donor

Used in the gas chamber of Geiger-Muller counters

Question 142

What is TLD? What is the mechanism of TLD? What’s the range of TLD?

Answer 142

 TLD = thermoluminescence device, a type of dosimeter
 Radiation crystal excites electrons into long-lived trap states
 Heating drops electrons from trap state to ground state produces detectable visible photons
 Range: 0.05 mSv-10 Sv

 Most common material: LiF

Question 143

Describe OSL?

Answer 143

optically stimulated luminescence (OSL) aluminum oxide (most common), quartz, feldspar, and irradiation produces valence electron ionization and electron/hole pair formation, the electron get trapped between the valence and conduction bands, irradiation causes excitation into the conduction band and the electron can that relax and recombine with the hole via fluoresence). Single site vs. multiple site read. OSL can differentiate dynamic (normal) vs. static (contamination of the detector) exposure.

Question 144

What are 4 advantages of NaI detectors? What are 2 disadvantages of NaI detectors?

Answer 144

Advantages:
o Good stopping power for 50-250 keV photons (photoelectric absorption)
o Efficient scintillator (1 visible photon/30 eV absorbed)
o Transparent to own scintillations
o Relatively inexpensive

Disadvantages
o Fragile
o Hygroscopic
o Higher γ energies Compton interaction dominates, requiring thicker crystal

Question 145

Compare NaI, BGO and LSO for their photon yield, density, atomic number and hygroscopic property

Answer 145

 Photon yield: NaI > LSO > GSO > BGO

 Density: LSO > BGO > GSO > NaI

 Zeff: BGO > LSO > GSO > NaI

 Hygroscopic: NaI yes, others no

Question 146

Name four crystals that are commercially available PET detector materials and rank them according to the following: density, light output and annihilation photon attenuation.

Answer 146

 Density: LSO, BGO, GSO, BaF2, NaI
 Light output: NaI, LSO, GSO, BGO, BaF2
 Photon Attenuation: BGO, LSO, GSO, BaF2, NaI
 Decay Constant: BaF2 (shortest), LSO, GSO, NaI, BGO

Question 147

How does the decay constant affect PET performance?

Answer 147

 Decreased randoms: can shorten coincidence timing window
 TOF imaging: higher SNR
 Decreased dead time losses: for high count rate studies

Question 148

Properties of PET crystals:
 given list of BGO, LSO, NaI, CsF, and BaF2
 asked which has highest light output, highest density, which is BEST for PET

Answer 148

 Light output: NaI
 Highest density: LSO
 LSO is best for PET

Question 149

Of 5 given PET scintillator materials (LSO, BGO, GSO, NaI, BaF2), which is the best for each of the following properties: effective z, density, stopping power, decay time, light output.

Answer 149

 Effective Z: BGO
 Density: LSO
 Stopping power: BGO
 Decay time: BaF2
 Light output: NaI

Question 150

Name 3 properties of detector crystal and rank them for NaI

Answer 150

 One of highest light output crystals
 Good stopping power for 50-250 keV, but poor compared to other PET crystals
 Inexpensive

Question 151

Which crystal is radioactive in PET (autoscintillation)? What is the nuclide? Is this important? Why or why not? (Lu-176)

Answer 151

 LSO, LYSO: 176Lu

 Theoretically autoscintillations can increase background

Question 152

Name the components of a photomultiplier tube

Answer 152

 photocathode – converts light photons into electrons

 focusing grid that directs the photoelectron to the dynode

 dynode – maintained at positive charge and attracts photoelectrons, producing many secondary electrons, which in turn are attracted to the next dynode, producing a large amount of current due to the electron multiplication factor

 anode – collects shower of electrons to produce the current

 glass housing to protect inside components and preserve vacuum inside tube

 stable high voltage supply

Question 153

Define detector efficiency? (I think they meant detection efficiency?) Describe each component of geometric efficiency equation?

Answer 153

D = g x e x f x F

Detection efficiency = efficiency with which a radiation measuring instrument converts emissions from a radiation source into useful signals from the detector

Geometric efficiency = efficiency with which the detector intercepts radiation emitted from the source, determined by detector size and distance from source to detector

Intrinsic efficiency = efficiency with which the detector absorbs incident radiation and converts them into potentially usable detector output signal, depends on detector thickness, composition, type and energy of radiation

f = fraction of output signals within PHA window

F = factor for absorption/scatter occurring within source or between source and detector

Question 154

List 4 parts of a liquid scintillation counter system

Answer 154

 Tube holder

 Scintillation fluid

 PMT

 Counting and energy discrimination electronics

Question 155

List 4 things in a liquid scintillation vial and explain briefly

Answer 155

 Liquid scintillation counter is used to count B emitters such as H-3 and C-14 which would be absorbed in the glass or plastic of test tube used in a well counter. Also used to count low energy x- & gamma rays not detected efficiently by NaI detectors.

 organic solvent – dissolves scintillator material and radioactive sample; absorbs most radiation from sample and transfer energy to scintillator molecules

 primary solute (or fluor) – absorbs energy from solvent and emits light

 secondary solute (waveshifter) – absorb emissions from primary solute and re-emit photons of longer wavelength which are better matched to PMT response

 additives – improve some aspect of LS performance, eg energy transfer efficiency from solvent to primary solute

Question 156

Three approaches to quench correction for liquid scintillation counting?

Answer 156

 Internal standardization method
o Count twice, with and without added standard

 Channel ratio method
o Count once, in 1 channel to be unquenched, channel 2 is quenched

 Automatic external standardization method
o Unshielding/shielding of an external standard source

Question 157

Name 3 reasons why semiconductor gamma cameras have not been produced until now.

Answer 157

 The 3 reasons have to do with the advent of CZT
o 1.Previously semiconductor crystals required storing (because of condensation of Li) and operation (thermal current=noise) at very low temperatures (liquid N2)
o 2.Only very thin (max 1cm) detectors could be produced because of the difficulty in avoiding impurities (HPGe), and this process was extremely expensive.
o 3.Very expensive because of these.
o 4.CZT is also denser than the other two.

 Advantages:
o more efficient absorber of radiation
o larger electrical output signal per unit of radiation absorbed
o can do energy-selective radiation counting

Question 158

Give energy resolution in %FWMH for NaI and CZT/CdTe?

Answer 158

 Varies depending on experimental setup: typically ~13% for NaI and 3-4% for CZT

Question 159

what’s the significance of good energy resolution

Answer 159

 Accurate spectroscopy

 Can narrow acceptance window to reject scatter

Question 160

You want a CZT, list 4 reasons you can provide to hospital board to convince them to buy it?

Answer 160

 ↓ imaging time for same quality of images
 Can ↓ patient dose while maintaining same diagnostic quality
 Higher spatial resolution (ability to separate normal from abnormal activity)
 Better quality images for obese patients due to improved energy resolution and scatter rejection

Question 161

What are the components of a well counter? What is a well counter used for? What are advantages and disadvantages of a well counter compared with a dose calibrator? liquid scintillation counter?

Answer 161

 Components
o Well within a detector crystal
o PMT
o Shielding
o Counting circuitry

 Used for highly sensitive energy-selective counting
o Radioimmunoassays
o Radioactivity in blood/urine samples
o Radiochemical assays
o Radiopharmaceutical quality control
o Wipe tests

 Advantages/Disadvantages
o More sensitive than dose calibrator
o Paralyzable; susceptible to dead time losses

Question 162

The patient is given 2 mGy of α tracer and 2 mGy of β tracer, what is the dose equivalent?

Answer 162

wR = 20 for α, 1 for β, so:

α ~40 mSv, β ~ 2 mSv.

Weighting factors :
x-rays; gamma; electrons; positrons; muons = 1
neutrons: < 10keV = 5
                10-100 keV = 10
                100 keV-2MeV = 20
                2 MeV-20MeV = 10
                > 20 MeV = 5
protons = 2 (if > 2MeV)
alpha particles; fission fragments; heavy nuclii = 20

Question 163

Define effective dose, equivalent dose

Answer 163

H = absorbed dose

 Equivalent dose = H x wR
o wR = radiation weighting factor

 Effective dose = H x wR x wT
o wT = tissue weighting factor

 Equivalent dose: absorbed dose modified to take into account the different biological damage produced by certain types of radiation:

 Effective dose: absorbed dose from a specific type of radiation modified to take into account different organ radiosensitivity:

Question 164

Define stochastic effect and deterministic effect and give an example of each

Answer 164

 Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose
o Example: cancer

 Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose
o Example: cataract

o Examples: myelosuppression, skin erythema, cataracts (200 rad), temporary male sterility (15-30 rad), permanent male sterility (400-600 rad)

Question 165

Define stochastic effect, deterministic effect. Give 2 examples of each. Which one is ALARA trying to prevent?

Answer 165

• Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose
o Example: cancer and heritable mutations

• Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose
o Example: cataract and skin erythema

• ALARA -> stochastic effects

Question 166

List in order of sensitivity various tissues. The ones listed were skin, gonads, bladder and lungs. But you may need to know other ones. There was hepatocytes, muscle cells and neuro tissue.

Answer 166

Sensitivity refers to deterministic effects, which are not exactly equivalent to tissue weighting factors

Testes > Bone marrow aplasia > Ovaries > Lung > Liver > Brain > Skin > Muscle (adult) > Bladder

PLUS SEE PAGE 94 OLD DOC

Question 167

Define weighting factor. Which 2 organs have the highest weighting factor?

Answer 167

 Tissue weighting factor: ratio of stochastic risk from irradiation of a specific tissue compared with the risk when the whole body is irradiated

ICRP 103: breast, RBM, lungs, colon, stomach (0.12), gonad (0.08 only)

Question 168

Relative radiosensitivies of different cell types?

Answer 168

Very high = lymphocytes; immature hematopoetic cells; spermatagonia

High = urinary bladder epithelium; gastric mucosa

Intermediate = liver, pancreas, thyroid, nerve cells

Low = muscle cells; connective tissue; bone and cartilage

Question 169

Basis of MIRD calculations

Answer 169

MIRD method, aka absorbed fraction method, allows calculation of radiation dose delivered to a target organ from radioactivity contained in one or more source organs in the body.

 amount of activity and time spent by the radioactivity in the source organ are determined
 total amount of radiation energy emitted by the radioactivity in the source organ is calculated.
 fraction of energy emitted by the source organ that is absorbed by the target organ is determined.

Question 170

What is reciprocal theory in dosimetry calculation?

Answer 170

 The theory states that for a specific organ pair, the specific absorbed fraction is the same, regardless of which organ is the target and which is the source.

Question 171

Factors that determine radiation exposure:

Answer 171

Extrinsic:
o Type of radiation
o Time
o Distance
o Shielding

Internal:

1) Total amount of activity and T1/2 effective of the radionuclide in the source organ
2) Amount of radiation energy emitted per activity
3) Fraction of radiation energy emitted that is absorbed by any target organ.

Question 172

Dose to gonads after 131I-iodide therapy?

Answer 172

For 5.5 GBq dose (150 mCi) = 0.141 Gy testes; 0.208 Gy for ovaries

Question 173

Effective dose of various radiopharmaceuticals:

Answer 173

Effective dose in mSv/MBq

I131&raquo_space; InWBC > Thallium > I131MIBG

Question 174

What is free radical? What does it do?

Answer 174

 An atom, molecule or ion with unpaired electrons or in an open shell configuration, which tend to be highly chemically reactive, and typically have a half-life 10^-10 to 10^-5

 Can cause breakage of bonds, such as in the DNA backbone

Question 175

Three features of a free radical.

Answer 175

 free (unbound) atom or molecule
 unpaired electron in outer shell
 highly reactive - short lifetime

Question 176

Define direct and indirect action of radiation. Which one causes damage that is easier to repair?

Answer 176

 Direct action: radiation (typically high LET) interaction with DNA

 Indirect action: radiation (typically low LET) interaction with other molecules, producing free radicals, that cause DNA damage

 Indirect generally easier to repair, as usually constitutes single strand breaks, while direct is more likely to cause double strand breaks

Question 177

What is hormesis? It happens at what level of absorbed dose?

Answer 177

Hormesis: paradoxical, beneficial effect of low dose ionizing radiation in biological systems

Possible mechanisms:
o Stimulation of defense mechanisms like antioxidant formation and DNA repair, leading to better repair of damage after subsequent high dose radiation

o Activation of anticancer immune functions

o Bystander effect to eradicate neighbouring cells with genomic instability

Question 178

Name the phases of mitosis and what happens to the DNA in each phase?

Answer 178

 Prophase: chromatin condensation
 Metaphase: chromosomes line up along equatorial plate
 Anaphase: sister chromatids split and migrate toward opposite poles
 Telophase: Chromatids reach destination, new nuclear membrane forms

Question 179

What are the 4 stages of the cell cycle, what is happening to DNA at each stage, and which is the most
radiosensitive and radioresistant of the 4 phases?

Answer 179

 G0/G1: DNA in euchromatin configuration for transcription
 S: DNA synthesis
 G2: DNA in euchromatin configuration for transcription
 M: chromatin condensation for mitosis

 Most radiosensitive in late G2/M
 Most radioresistant in late S

Question 180

4 R’s of radiobiology

Answer 180

Repair

Reassortment/redistribution

Reoxygenation

Repopulation/regeneration

Question 181

What is the difference in cell survival curves between high and low dose rate radiation exposure. Is this
true for all types of radiation? What is the reason?

Answer 181

Graph of Fraction of cells surviving vs Dose (Rad or Gy)

 “High dose rate is related to higher cell killing because the cells do not have the time to repair themselves.”

 No. The curve is not the same for all types of radiation.

 High dose: steep curve
 Decrease dose: get repair, less steep
 Decrease further, get reassortment/redistribution, steepens again (G2 pile-up)
 Decrease dose further, repopulation: less steep
 With high LET, less shoulder effect

Question 182

Draw the cell survival curves for neutrons, Beta (-) particles and xrays with labeling of the coordinates and
identifying which are the different LET particles.

Answer 182

Depends on energy of neutron (high energy has shoulder, lower energy more like alpha, linear

Question 183

describe LET and significance in radiobiology

Answer 183

Linear energy transfer (LET) = amount of energy deposited locally per unit track length

Significance
o Relative biologic effective (RBE) increases with LET until a maximum (100 keV/μm), then decreases
with higher LET
o Because 100 keV/μm corresponds to ionizations ~2 nm = width of DNA strand

Question 184

Define the doubling dose and how much is it?

Answer 184

 Dose to whole population required to double spontaneous mutation rate in population

Question 185

Define the dose to an individual for a procedure multiplied by the number of procedures per year, what is that called?

Answer 185

“the overall population impact of diagnostic radiology can be assessed in terms of the collective effective dose, the product of effective dose and the number of individuals exposed.”

Question 186

Define ‘genetically significant dose’ GSD

Answer 186

GSD = index of radiation received by the genetic pool

o Di = the average gonad dose for a specified type of examination for a patient in age-sex class (i)

ni = the number of persons in age-sex class (i) who had the specified type of examination during a year

Pi = the expected number of future children to an individual in age-sex class (i) o Ni = the number of persons in age-sex class (i) in the total population

Question 187

define GSD and give GSD for x-ray, gamma ray and background

Answer 187

 GSD = index of radiation received by the genetic pool

NCRP #93 (1987)
o Natural: 1 mSv (radon (0.1) + other (0.9))
o Diagnostic X-rays: 0.2-0.3 mSv
o Nuclear medicine: 0.02 mSv

Question 188

In relation to carcinogenesis, define “initiation”, “promotion” and “propagation”

Answer 188

 Initiation: mutation of DNA resulting in genomic instability

 Promotion: action of a promoter (e.g., molecule) upon cell after initial mutation to induce clonal proliferation
o E.g., ionizing radiation can promote proliferation by affecting tumour suppressor gene

 Propagation: stepwise transition to cancer: tumour cells undergo dysregulated proliferation due to second “hit”/mutation, with loss of tumour suppressor genes or activation of oncogenes

Question 189

What is the Bergonie-Tribondeau rule and name 2 cell types which are exceptions?

Answer 189

X-rays are more effective on cells which have a greater reproductive activity:
o Therefore, cells that are rapidly dividing, undifferentiated and have long mitotic futures are most radiosensitive

 Exceptions
o Small lymphocytes
o Primary oocytes

Question 190

What is the effect of oxygen on radiation damage to cells?

Answer 190

 Oxygen enhances radiation damage

 Oxygen fixation hypothesis: oxygen converts DNA radical to non-restorable form, preventing repair

Question 191

What is the effect of oxygen on radiation? Define oxygen enhancement ratio (OER) & describe molecular basis of action.

Answer 191

 Oxygen fixation hypothesis: oxygen converts DNA radical to non-restorable form, preventing repair

 OER = ratio of dose under hypoxic to aerated conditions needed to achieve the same biological effect
 X-ray: 2.5-3.5
 n = 1.6
 α = 1.0

Question 192

What are characteristics of radioprotectors and how do they function?

Answer 192

 Radioprotectors are chemicals that reduce the biologic effects of radiation. Sulfhydryl compounds (free SH group) such as cysteine and cysteamine work by
o free radical scavenging
o hydrogen atom donation to facilitate direct chemical repair at sites of DNA damage

Question 193

Typical structure of a radiation protector. (What is the chemical basis of radioprotectors?) What is the mechanism?

Answer 193

Sulfhydryl group at one end

Base (NH2) at the other

Carbone chain in between

The most effective radioprotectors contain a sulfhydryl group, often covered by a phosphate group to reduce toxicity

Question 194

Describe stochastic effect, deterministic effect, what is hereditary effect, cataract and what part of eye affected in cataract?

Answer 194

 Stochastic effect-No threshold, increase in dose increases likelihood of effect but not its severity.

 Deterministic effect-Threshold, increase in dose increased severity of the effect.

 Hereditary effect-These are mutations that occur in the offspring of irradiated individuals. They originate in the haploid cells of the reproductive system (oocytes and spermatozoa) and are passed on to offspring that are conceived after irradiation. My not occur in the first gen., model for dose response relationship is the no threshold, linear model.

 Cataractogenesis-any opacification of the normally clear lens. 2 Gy threshold, usually posterior pole of the lens in radiation induced.

Question 195

Know the 4 syndromes of acute radiation exposure and doses, clinical symptoms associated with each.

Answer 195

 Threshold dose for prodrome 0.5 Gy
 LD50/60 in humans ~4 Gy
 Minimum dose for lethality 2.5 Gy (Hall), 1 Gy without good medical care (ICRP)

1. Prodromal radiation syndrome:
   o 0.5-1 Gy – early symptoms soon after radiation
   o Neuromuscular
    easy fatigability, apathy, listlessness, sweating, fever, HA, hypotension
   o GI
    anorexia, N/V, cramps, dehydration, immediate diarrhea
2. Hematopoietic syndrome
   o 2.5 -5 Gy
   o prodromal symptoms including N/V, followed by a latent period, then symptoms of depressed of blood elements: infection and fever from granulocyte depression; bleeding and possibly anemia caused by hemorrhage from platelet depression; anemia from RBC depression usually does NOT occur.
3. Gastrointestinal syndrome
   o 5 – 12 Gy (~ 10 Gy)
   o N/V, prolonged diarrhea, anorexia, dehydration, weight loss, death (5-10 days)
4. Cerebrovascular syndrome
   o ~ 100 Gy
   o severe N/V, disorientation, loss of coordination of muscular movement, respiratory distress, diarrhea, convulsive seizures, coma and finally death (24-48 hr)

Question 196

Dose for bone marrow aplasia??

Answer 196

o TD5/5: 2.5 Gy (tolerance dose, 5% in 5 y)

o TD50/5: 4.5 Gy (tolerance dose, 50% in 5 y)

Question 197

Why is there a lag in the Hematopoietic Syndromes symptoms

Answer 197

 Symptoms result from reduction in specific blood elements, which have different average life spans

 Lymphopenia (1-2 days) → neutropenia (10-14 d) → thrombocytopenia (14d) → anemia (60 days)

Question 198

In utero exposure, threshold dose of lethality at varied stages

Answer 198

 Embryonic lethality thresholds (IAEA)
o 1st trimester: 100 mGy
o 2nd : 250 mGy
o 3rd: 500 mGy

Question 199

What is the lowest limit of exposure for fetal death in the following stages of pregnancy: 0-2 weeks, 2-7 weeks, 8-15 weeks, 15-21 weeks, greater than 21 weeks

Answer 199

o <1 week; 0.05-0.1 Gy
o 1-8 weeks; 0.25-0.5 Gy
o 8-15 weeks; 0.5 Gy
o 15-25 weeks; >0.5 Gy
o >25 weeks; >1.0 Gy

Question 200

3 main factors in radiation protection. What happens to radiation flux if you triple the distance? (What are the three most important factors in relation to gamma exposure?)

Answer 200

 Time, distance and shielding

 What happens to radiation flux if you triple the distance?
o Decreased by 1/9

 Most important factors relating to gamma exposure?
o Time
o Distance
o Shielding
o Decay
o Energy

Question 201

What affects effectiveness of shielding?

Answer 201

 Effective Z (high Z for photon; low Z for particulate)
 Density (higher density for photon; doesn’t matter for particulate)
 Thickness
 Type of radiation shielding against

Question 202

What is responsible for the greatest radioactive exposure for background radiation. What is the physiologic internal radioisotope that causes the most radiation exposure in humans.

Answer 202

 From natural background: radon

 Physiologic internal radioisotope: 40K

Question 203

2 isotopes which cause largest amount of internal radiation

Answer 203

K-40

C14

Question 204

Couple questions on Chernobyl. What the most cancer was, why the observed cancer rate was less in some, and three explanations for the same.

Answer 204

 Most common: thyroid cancer

 Cancer rates depended on:
o Heterogeneous distribution of radioactive gases and particles containing 131I
o Radioiodine consumption variable, typically from contaminated milk and produce
o Age of exposed individuals (younger more susceptible)

1.pediatric thyroid is more susceptible

Question 205

Definition of Nuclear Energy Worker. What’s the limit of radiation exposure to pregnant NEW?

Answer 205

 A NEW is any person who in the routine performance of their profession, business or employment will expect to be exposed to more than the prescribed limit of ionizing radiation for the general public

 Public = 1mSv per year; lens 15; skin 50; hands/feet 50 (1/10th of NEW)
 Pregnant = 4 mSv during course of pregnancy
 NEW = 50 mSv one year, 100 mSv over 5 consecutive years; lens 150; skin 500; hands/feet 500

Question 206

What are the laboratory rules (5) for contamination control in an intermediate lab?

Answer 206

 Wear protective clothing and equipment (gloves, lab coat)
 Do not eat, drink, store food, or smoke in this room.
 Wear appropriate dosimeter at all times
 In case of spill, follow emergency procedures and notify the RSO
 Clearly identify work surfaces used for handling nuclear substances
 After working with nuclear substances, monitor work area for contamination
 Wash hands regularly and monitor them for contamination frequently
 Check all packages containing nuclear substances for damage upon receipt
 Store nuclear substances in a locked room or enclosure when not in use.

Question 207

What is the radioactivity level for an intermediate lab?

Answer 207

Basic lab: Quantity of unsealed nuclear substance used at a single time does not exceed 5 times its corresponding annual limit on intake

Intermediate - <50x

High - < 500x

Containment level - >500x

Annual Limit on Intake (ALI)-The activity, in Becquerels, of a radionuclide that will deliver an effective dose of 20 mSv during the 50-year period after the radionuclide is taken into the body of a person 18 years old or older or during the period beginning at intake and ending at age 70 after it is taken into the body of a person less than 18 years old.

 The amount of radioactivity that would deliver 20 mSv after ingestion over the 50 year period after ingestion
 By definition, 1 ALI = 20 mSv/DCF (dose conversion factor)

Question 208

Name the contamination for each class (class A, B and C)

Answer 208

CNSC license (non-fixed contamination in area with unsealed nuclear substance)

 Removable contamination not to exceed these limits when averaged over surface area <100 cm2:

 For controlled areas: 
o 3 Bq/cm2 for class A radionuclides (Co56, Co60)
o 30 Bq/cm2 for class B radionuclides (F18, I131, I111)
o 300 Bq/cm2 for class C radionuclides (Tc99m)

 For supervised public areas and for decommissioning (1/10th of controlled area dose
o 0.3 Bq/cm2 for class A radionuclides 
o 3 Bq/cm2 for class B radionuclides 
o 30 Bq/cm2 for class C radionuclides

Question 209

Name 3 or 4 tests to which type A containers are subjected

Answer 209

 Water spray test
 Free drop test
 Stacking test
 Penetration test

Question 210

For three categories of radioactive packages what are the radiation levels on the surface and at 1 meter distance?

Answer 210

 TI = maximum radiation level in uSv/hr at 1 m from external surface of package, divided by 10, or in mSv/h multiplied by 100.

Type of label; surface (uSv/h); 1m TI
 White - I < 5 < 0.5 < 0.05
 Yellow - II <500 < 10 < 1
 Yellow - III < 2000 < 100 < 10

Question 211

radiation level limits at surface of 3 types of packages – know your TDG

Answer 211

 There are 4 types of packages.
 Excepted packages
 White 1
 Yellow 2
 Yellow 3

Question 212

TDG, surface dose rates for all 3 levels. (Three types of radioactive packages: name, and state maximum radioactivity at surface)

Answer 212

 Excepted packages (UN 2910)

 Radioactive I (White-I): surface dose rate <=5 uSv/h and activity >excepted package limit

 Radioactive II (Yellow-II): 5 uSv/h < Package surface <=500 uSv/h and transport index <=1.0

 Radioactive III (Yellow-III): Package surface >500 uSv/h or transport index >1.0

 Transport index = highest dose rate (uSv/h) at 1 meter, divided by 10

 Fissile
 Surface contamination: surface quantities >0.3 Bq/cm2 for beta and gamma and low toxicity alpha emitters; 0.03 Bq/cm2 for other alpha emitters

Question 213

Define the gamma constant-exposure or dose

Answer 213

 Specific gamma ray dose constant = exposure rate per unit activity at a certain distance from a source

 Unshielded dose equivalent rate at one meter in mSvh-1MBq-1

Question 214

List 5 steps to take when opening a package containing radionuclide shipment.

Answer 214

CNSC Guidelines for Handling Packages Containing Nuclear Substances

o 1. If an appropriate survey monitor is available, monitor the radiation fields around the package. Note any discrepancies.

o 2. Avoid unnecessary direct contact with unshielded containers.

o 3. Verify the nuclear substance, the quantity, and other details with the information on the packing slip and with the purchase order. Log the shipment details and any anomalies in the inventory record.

o 4. Report any anomalies (radiation levels in excess of the package labeling, incorrect transport index, contamination, leakage, short or wrong shipment) to the Radiation Safety Officer.

 When opening packages containing unsealed nuclear substances, additional steps should be taken:
o 5. Wear protective clothing while handling the package.
o 6. If the material is volatile (unbound iodine, tritium, radioactive gases, etc.) or in a powder form, open the package in a fume hood.
o 7. Open the outer package and check for possible damage to the contents, broken seals, or discoloration of packing materials. If the contents appear to be damaged, isolate the package to prevent further contamination and notify the Radiation Safety Officer.
o 8. If no damage is evident, wipe test the inner package or primary container which holds the unsealed nuclear substance. If contamination is detected, monitor all packaging and, if appropriate, all locations in contact with the package, for contamination. Contain the contamination, decontaminate, and dispose in accordance with the conditions of the Nuclear Substances and Radiation Devices licence.

On receipt of a package, and on opening a package, every person shall verify whether
o the package is damaged;
o the package shows evidence of having been tampered with;
o any portion of the fissile material is outside the confinement system; and
o any portion of the contents of the package is outside the containment system or the package.

Question 215

List 4 steps to take when opening a package containing radionuclide shipment?

Answer 215

 Document receipt of package (date, consignor, activity, etc.)
 Inspect for damage or tampering
 Survey: measure exposure rate at 1m and at surface
 Wipe test outer surface >300cm2
 (Open outer package and check for internal leaks)

Question 216

A question on bioassay – how frequently performed for I-131 and at what level of detection a report to CNSC needs to be made.

Answer 216

 Between 1-5 days after exposure
 >= 10 kBq is reporting level

 5 days after administration of treatment dose;
 1000 Bq-investigation limit
 10000 Bq-reporting limit

Question 217

What are routine and non routine bioassays as determined by the CNSC (RD-58)?

Answer 217

o A “routine” radiobioassay is any radiobioassay that involves collecting and analyzing samples or taking measurements on the body at scheduled intervals, or at predetermined times, during normal operations.
o A “non-routine” radiobioassay is any radiobioassay that is implemented as part of an ad hoc response to a particular circumstance, such as a known or suspected intake of radioactive material due to an abnormal incident in the work place. “Non-routine” radiobioassays are often termed “ad hoc” or “special” radiobioassays.

Question 218

What are doses for allowing a patient to be treated with thyroid therapy as an outpatient?

Answer 218

The actual definition is:
o Discharge and outpatient criteria should be based on the anticipated dose to members of the public (kept below 1mSv) and to the primary caregiver (kept below 5 mSv per IAEA recommendations).

o Discharge criteria at the CCI are in line with this – dose rate at 2m < 18 uSv/hr.

Question 219

3 methods (treatments) of decreasing contamination from internal radiation?

Answer 219

 Thyroid blockade (competitive inhibition)
 Hydration/frequent voiding (physiologic excretion)
 Cathartics/laxatives (direct extraction/physiologic)

Question 220

CNSC definition of “action level”. What is the response if a situation reaches that “action level” in your practice.

Answer 220

 Action level = specific dose of radiation or other parameters, if reached, may indicate a loss of control of part of licensee’s radiation protection program and triggers a requirement for specific actions to be taken

 Response: inform the RSO, who will perform the investigation

Question 221

What 3 things to do according to CSNC when an action level is reached?

Answer 221

 1.Conduct and investigation and determine a cause
 2.Identify and take action to restore the effectiveness of the radiation safety program
 3.Notify the CNSC within the time specified on the licence.

Question 222

What is the Quality Control for sealed sources containing > 50 MBq? Minor spill: < 100 exemption quantity (EQ) of a nuclear substance
 Major spill:
o > 100 EQ
o personnel contamination
o release of volatile material

Answer 222

 Perform a leak test in the following frequencies:
o i) For each sealed source continuously in storage - every 24 months;
o ii) For each sealed source which is incorporated in a device - every 12 months;
o iii) For each sealed source or shielding that is to be used after being stored for 12 or more consecutive months – immediately before using it;
o iv) For any other sealed source over 50 MBq (i.e. if used daily) – every 6 months.

Question 223

If worker exposed to significant 131I dose what is the first thing you should do? In what time range should gamma probe counting be performed? When should the CNSC be notified?

Answer 223

 If spill present, contain and decontaminate
 Administer thyroid blockade (130 mg potassium iodide) and inform RSO
 Gamma probe: between 1-5 days after exposure
 If >=10 kBq inform CSNC immediately
 If <10 kBq, >1 kBq, then include in annual compliance report

Question 224

3 characteristics that define a major spill.

Answer 224

Minor spill: < 100 exemption quantity (EQ) of a nuclear substance

Major spill:
o > 100 exemption quantities
o personnel contamination
o release of volatile material

Question 225

How is an Exemption quantity define (used to be called “scheduled quantity”)

Answer 225

 Defined in Nuclear Substances and Radiation Devices Regulations as one of the thresholds for quantity of radioactive nuclear substance below which activites may be carried on without a licence

 Exemption quantities differ for each radionuclide and are given in Schedule 1

Question 226

List 8 steps to take with a radioactive spill?

Answer 226

 Clear the area
 Leave fume hood running
 Close off and secure spill area
 Notify RSO
 Remove contaminated clothing and clean skin
 Clean spill working from outside in
 Wipe test for residual contamination as appropriate
 Arrange bioassay if necessary
 Submit written report

Question 227

Tc-tagged RBC vial, what are 3 categories of materials it can be disposed of in?? What are the 3 types of waste it is considered to be (when you throw away a used
syringe with tagged RBC)?

Answer 227

 Biologic, radioactive and sharps

Question 228

What is the duration of a CNSC licence for therapeutic and diagnostic nuclear medicine.

Answer 228

 5 year licence, annual compliance report

Question 229

What are the roles of the radiation safety officer?

Answer 229

 Availability: full-time

 Training: basic radiation safety

 Annual review
o Check dose limits
o Quarterly contamination monitoring

 Incidents
o Investigations of contamination, overexposure, etc.

 Disposal
 Emergency planning
 Records
 Survey instrument QC

Question 230

Who is ultimately responsible for running the hospital? How does the hospital check up on the physician?

Answer 230

 Day to day: Executive Team, lead by President/CEO
 Policy makers: Board of Directors
 Level of authority may differ, e.g., some hospitals have own board, others run by health region
 Hospital medical director typically oversees physician privileging and performance

Question 231

Discuss the 4 groups of recommendations of the ICRP with regards to breast feeding discontinuation following radiopharmaceutical administrati

Answer 231

1. No cessation: 
 Most Tc
 C14
 FDG
 In-111-octreotide/WBCs

2. 12 hour cessation: 
 TcWBCs, 
 Maa
 Pertechnetate
 RBCs
 I123

3. 48h
    TI201
4. > 3 weeks
    I131
    Ga67

Question 232

In what form does technetium appear in the breast? In what form does gallium appear in breast milk?

Answer 232

 Tc-pertechnetate (10% in breast milk)

 Ga-lactoferrin

Question 233

Radiation workers are exposed to 15,000 roentgens per hour and are exposed for a total of 1 hour. The tech is 1 meter away, the engineer is 3 meters away, the secretary is 15 meters away. What type of effects is the engineer likely to experience? The secretary is 8 weeks pregnant. What would you suggest for management for her? What is the expected effects to the tech?

Answer 233

 Tech @ 1m:
o 15,000 R/h x 1h = 15,000 R
o 1 R = 0.96 rad in soft tissue
o D = 0.0096 x 15,000 R = 146 Gy
o CNS syndrome

 Engineer @3m:
o D = 146 Gy/3^2 = 16.2 Gy
o GI syndrome

 Secretary @15m:
o D = 146 Gy/15^2 = 0.65 Gy
o Counsel re: mental retardation, growth retardation
o Slight increase childhood cance risk, increased lifetime cancer risk
o >100 mGy considered threshold for therapeutic abortion

Question 234

Patient received a high dose of 131I and was sent to OR the same night. What are the instructions that you give the surgeons regarding radiation safety?

Answer 234

Most of dose will be in region of urinary bladder
Minimize exposure to bodily fluids.
Wear gloves, masks, work in shifts to minimize exposure
Consider SSKI/thyroid blockade

Question 235

Four disposal methods for radioactive waste:

Answer 235

 Decay in storage
 Release into sewer system
 Transfer to authorized recipient (e.g., landfill)
 Incineration/atmospheric release

Question 236

What is iodine escape peak? What is the lead peak? What is the single coincidence escape peak?

Answer 236

 iodine escape peak - interaction with iodine in NaI(Tl) results in characteristic X-ray (30 keV) which escapes detector; therefore, iodine escape peak @ Eγ - 30 keV

 lead peak - interaction of photon with lead in collimator results in characteristic X-ray (80-90 keV), which is absorbed by detector

 single escape peak - occurs as a result of pair production; annihilation of positron results in two 511 keV photons of which only 1 is absorbed in detector; occurs at 511 keV

Question 237

If a patient is having a technetium bone scan and a thallium study on the same day, which study do you do first and why?

Answer 237

201Tl study first:
o Lower dose
o Less downscatter effects

Question 238

What is z signal coming from the anger camera?

Answer 238

 Z-signal = summation of output of all PMT, proportional to the total amount of light produced by a scintillation event in the crystal and used for pulse height analysis

Question 239

Typical FOV for gamma camera? What affects the FOV

Answer 239

• Philips Brightview XCT: 50x40 cm FOV with parallel-hole collimator

Question 240

Relationship between gamma camera efficiency and photon energy?

Answer 240

• Intrinsic efficiency ↓ with ↑ photon energy

Question 241

A question asking for the frequencies of doing the following for a gamma camera: intrinsic uniformity, spatial linearity, system resolution, sensitivity.

Answer 241

o Intrinsic uniformity: daily (EANM, CPSA, ACR, ICANL, AAPM)
o Spatial linearity: weekly (Zanzonico, ICANL)
o System resolution: weekly (ACR, ICANL)
o Sensitivity: weekly (EANM)

Question 242

Describe timing of various QC’s: know dose calibrator, spatial resolution, photopeak etc (Another recall: when and how do you assess: gamma camera resolution, gamma camera uniformity, gamma camera energy peak, dose calibrator linearity, dose calibrator constancy)

Answer 242

 Gamma camera resolution
o Bar phantom weekly with a flood source

 Gamma camera uniformity
o Intrinsic with a point source placed 5x detector face width away, collimator off

 Gamma camera energy peak
o Tc-99m point source daily
o Set to 140 +/- 10% window

Question 243

Describe how you would perform intrinsic uniformity test

Answer 243

 Remove collimator
 Place Tc-99m point source (<1 ml, ~18.5 MBq) in holder >= 5x crystal dimensions away, centered over uncollimated detector
 Count rate <25 kcps
 Acquire 10-15 million counts
 Determine integral and differential uniformity (<5%)

Question 244

Another question on intrinsic uniformity, once again define the ___ in SPECT

Answer 244

 <1% non-uniformity for SPECT

Causes of nonuniformity;
1. Nonuniform detection efficiencies due to i.small differences in pulse height spectrum of the PMTs and ii.position dependant detection efficiencies especially in the gaps between PMTs and

2. Nonlinearities.

Question 245

Related to the NEMA uniformity spec, how you determine integral and differential uniformity

Answer 245

 integral uniformity = (max pixel - min pixel) / (max pixel + min pixel) x 100
o including entire field of view for UFOV and central 75% for CFOV

 differential uniformity = (max pixel - min pixel) / (max pixel + min pixel) x 100
o including only the 5 contiguous pixels with greatest difference in either column or row

Question 246

Def: angular variation in a field of flood uniformity . How would you calculate it?

Answer 246

 Acquire flood images at multiple angles and compare. Maximum sensitivity variation should not exceed 0.75%. Note that this is no longer an issue as all PMTs are now magnetically shielded with mu metal.

Question 247

Briefly describe how to determine angular uniformity

Answer 247

Tape Co-57 sheet source to the collimator face
 Obtain high count tomographic acquisition over 360°C
 Assess uniformity visually on raw cine images

Question 248

Limits of non-uniformity. (What is the limit of non-uniformity for SPECT)

Answer 248

 Depends on manufacturer recommendations, but for our centre
o Integral: CFOV: 5%, UFOV: 6%
o Differential: CFOV: 2.5%, UFOV: 3%

 Also, depends whether talking about SPECT, in which case <1% after correction factors applied

Question 249

2 types of collimation in nuclear medicine

Answer 249

 Absorptive and electronic

Question 250

Question on different types of collimators and their effects on the image, i.e. magnification, inversion, etc

Answer 250

Pinhole:
- poor efficiency (worse with distance); highest resolution; magnifies; inverts

Parallel:
- Good efficiency; 3rd best resolution; No mag; no inversion

Converging (as looking from detector out to object):
- incresing effiency until focal point; 2nd best resolution; ; Magnifies; no inversion

Diverging (as looking from detector out to object)
- efficiency decreases with distance; worst res; minifies; no inversion

Question 251

Two changes which can be made to collimator holes to increase spatial resolution

Answer 251

 ↑ septal length

 ↓ hole diameter

Question 252

Collimator A is considered clinically superior to collimator B. Both are made of lead with identical hole spacing and septal thickness. A has 2mm better FWHM than B. Which is more sensitive and by how much? What is the physical difference between them?

Answer 252

 A has lower efficiency than B

Rcoll ∝ l/d, gcoll ∝ (d/l)2, the sensitivity decreases by the square of the leff while the Resolution varies linearly with it.

Question 253

3 characteristics of collimator and how they affect performance of NaI detector

Answer 253

 d = hole diameter: ↑d = ↑FWHM and ↑d = ↑efficiency
 leff = septal length: ↑leff = ↓FWHM and ↑leff = ↓efficiency
 t = septal thickness: ↑t = ↓efficiency

Question 254

describe pinhole collimator cone depth distortion

Answer 254

 Cone depth distortion-refers to image distortion of a three dimensional object that occurs because source planes are at different distances from the collimator are magnified by different amounts

Question 255

Define intrinsic efficiency of a gamma camera and describe what determines it.

Answer 255

 Intrinsic efficiency (ε) = # of radiation interacting with detector / # of radiation striking detector

 Factors: detector thickness & composition, type & energy of radiation

Question 256

Define intrinsic spatial resolution and name 3 things that determine gamma camera resolution. [French: How are these two related? What factors affect them?

Answer 256

Intrinsic spatial resolution = limit of spatial resolution achievable by the detector and electronics, ignoring additional blurring due to the collimator

Factors:
o Multiple scattering within detector
o Statistical fluctuation in distribution of light photons
o Gamma ray energy
o (Detector crystal thickness)

Question 257

In a system with a given intrinsic resolution (Rins) and a non-collinearity resolution (Rnc) and a given scatter resolution (Rsca), what is the system resolution (Rsys)?

Answer 257

Rsys = SQRT(Rins^2 + Rnc^2 + Rsca^2)

Question 258

What is a qualitative way of performing spatial resolution?

Answer 258

 Using a spatial resolution phantom (e.g., 4 quadrant bar or parallel line phantom) with flood source

 Note smallest bar pattern visible on image

Question 259

Define septal penetration. What is an acceptable rate of septal penetration for adequate image quality?

Answer 259

 Septal penetration = proportion of the off-angle photons passing through lead septae of collimator and detected in adjacent portion of scintillator
 <5%

Question 260

Filter question. Define Nyquist frequency:

Answer 260

 The highest spatial frequency that can be resolved in an image, based on resolution characteristics of the imaging system and the parameters selected for data acquisition (i.e., 0.5 cycles/pixel)

 Nyquist frequency (kmax) = highest resolvable spatial frequency

 Typically set linear sampling distance (Δr) = 1/(2 kmax)

 If Δr < 2 FWHM, can have aliasing
 If Δr < 1/3 FWHM, sufficient sampling
 If Δr > 2 FWHM, definitely will have aliasing
 If Δr = FWHM, will have aliasing
 If kmax significantly exceeded, may have over-sampling, resulting in lower counts per pixel, and possibly excessive noise

Question 261

How to avoid aliasing?

Answer 261

 Make sampling interval small enough (but may be impractical because of dataset size, computation time, etc.)

 ↓ FOV, with sample # of samples (so ↓Δx)

 Blur input profile before recording (suppress high frequency components)

Question 262

Describe how you choose optimal acquisition matrix. Give an example. 2 problems with assigning an acquisition pixel size which is smaller than necessary.

Answer 262

Spatial resolution of digital image dependent on 2 factors:
o resolution of imaging device itself (collimator/detector resolution)
o matrix size

 A matrix size is chosen so that the highest possible frequency signal acquired can be fully represented (i.e. the spatial resolution limit of the system can be displayed), pixel size<1/2kmax (FWHM/3). Once this limit is met, increasing matrix size only results in increasing noise and time and memory requirements.

 Set pixel size (Δr) <= 1/3 FWHM
 Acquisition matrix for square planar FOV = FOV/Δr by FOV/Δr
 If Δr too small:
o Too few counts/pixel  high statistical noise
o ↑ pixels  ↑memory usage

Question 263

Given the MTF values of .8, .7 and .6 for three different systems at a particular frequency, which has the best response?

Answer 263

 0.8, the closer to unity the more faithfully the image will be represented at that spatial frequency.

Question 264

How do you calculate the MTF for the system from MTFa and MTFb.

Answer 264

MTFsystem = MTFa x MTFb

Question 265

Define MTF. Qualitatively describe the relationship between MTF and the line spread function. How can knowing the MTF of different collimators affect the purchase decision

Answer 265

 MTF = modulation transfer function, describe the spatial frequency response of an imaging system or component
o MTF is the modulus of the discrete Fourier transform of the measured line spread function
 MTF helps compare the how faithfully collimators reproduce image at different spatial frequencies

Question 266

Draw a ramp filter in the frequency domain. Draw a point spread function in one projection in the spatial domain after FBP. What are 1 difference and 1 similarity between recovery filter and low pass filter. Additional question - Draw a point source after FBP and ramp filter in the frequency domain?

Answer 266

 Draw ramp with boxcar (i.e., truncated)
 Square with black stripe
 Recovery filter vs. low pass filter
o Similarity: both truncate at a maximal spatial frequency
o Difference: recovery filter amplifies medium to high spatial frequencies

SEE PAGE 157 for diagram

Question 267

Question on what factors contribute to optimal thickness of sodium iodide crystal.

Answer 267

 Intrinsic efficiency vs. intrinsic spatial resolution
o Thinner crystal = better resolution
o Thicker crystal = better efficiency

 Energy of incident photon

Question 268

A question on factors that contribute to decreased spatial resolution in sodium iodide detector.

Answer 268

 ↓spatial resolution:
o Multiple Compton scattering
o Statistical variation in light photons among PMT
o Gamma ray energy
o Detector crystal thickness
o Efficiency
o Corrections for non-linearity

Question 269

What causes variation in energy resolution in a sodium iodide detector?

Answer 269

o Statistical variations in the number of scintillation light photons produced per keV of radiation energy deposited
o Statistical variations in # of photoelectrons released from photocathode
o Statistical variations in electron multiplication factor of the dynodes in PMT
o Non-uniform sensitivity to scintillation light over area of PMT cathode
o Non-uniform light collection efficiency for light emitted from interactions at different locations within detector crystal
o Nonlinear energy response of the scintillator
o Fluctuations in high voltage applied to PMT
o Electrical noise in PMT

Question 270

Effect of scatter on the performance of a gamma camera?

Answer 270

 Scatter in crystal  ↓intrinsic spatial resolution
 Scatter in crystal (especially escaped)  likely rejected, ↓efficiency rather than energy resolution
 Scatter in crystal (especially escaped)  ↓count rate performance within energy window
 Scatter in patient  may be accepted, decreased spatial resolution

Question 271

What is a sinogram and what is it useful for? What are the axes labelled with?

Answer 271

 Y-axis: angle of projection
 X-axis: projection profile intensity
 Use: assess motion & non-uniformity

Question 272

Besides CNR, what other types of noise are found in nuclear medicine studies?

Answer 272

 CNR usually dealing with random noise
 Structured noise: non-random, e.g., artifact relating to non-uniformity
 scatter, blunders (ie. motion), systematic error (i.e. COR off)

Question 273

What is resolution recovery? How does resolution recovery affect the recovery coefficient?

Answer 273

 Filtering that helps to more accurately represent the intensity/activity of small hot objects (<2xFWHM), i.e., they are reduced due to partial volume effects, so resolution recovery will increase their intensity
 The recovery coefficient overall improves (i.e., function rectangularizes) with resolution recovery, such that it is higher at the mid to higher spatial frequencies

Question 274

How can resolution variability with depth in SPECT be corrected for?

Answer 274

 Can do this during iterative reconstruction

Question 275

Four configurations of transmission source of SPECT imaging:

Answer 275

 Scanning line
 Dual scanning line
 Flood
 Stationary line source with fan beam collimator

Question 276

What are the advantages of 2D vs 3D PET and by how much is sensitivity better in 3D PET?

Answer 276

 Advantages of 2D
o Less scatter
o Lower single count rate, fewer random events
o Reconstruction is less complicated

 Sensitivities:
o 3D PET: 2-10%; 2D PET: 0.2-0.5% (4-8x) (2D is 4-8 times less sensitive than 3D)

Question 277

Name three events/interactions on PET imaging:

Answer 277

o True coincidence
o Scatter coincidence
o Random concidence

Question 278

List 2 ways to decrease random & 2 ways to decrease scatter radiation in PET?

Answer 278

 Decrease randoms
o Delayed window method (create a delayed timing window with a time offset from coincidence timing window (CTW). Events recorded in the delayed window provides a measure of random event rate and is subtracted from the total number of coincidence events since random coincidence rate is the same in delayed and undelayed windows)
o Singles count rate method

 Scatter reduction
o Gaussian fit to scatter tail
o Monte Carlo simulation method

 Utilize emission and transmission images to estimate Compton scatter
o Convolution/deconvolution

Question 279

What is “time of flight” theory? What’s the advantage of applying it to PET image?

Answer 279

 Accurate measurement of arrival times of annihilation photons theoretically allows localization of annihilation event along line of response, but in practice, insufficiently precise to improve spatial resolution, but improves SNR

Question 280

Questions of time of flight and crystals used and how it works and what characteristics of crystal are best for tof.

Answer 280

 ToF PET images has higher SNR.
 Need fast scintillator and electronic circuits to work. BaF2 has fast response speed, but it has lower stopping power
 LYSO is the scintillator crystal used for ToF PET because it has reasonably fast response, good stopping power and good energy resolution

Question 281

2 limitations in using TOF for image production. Which is the major one? (If TOF PET were exact, iterative reconstruction would be unnecessary. What prevents PET TOF determination from being exact? Very similar version later asked for the two factors limiting depth resolution in TOF PET.)

Answer 281

 Crystal rise time and decay constant (major factor)

 Time jitter due to finite # of photoelectrons

Question 282

What is the “time of flight” theory? Which crystal can be used for TOF? name 3 characteristics needed for a crystal for time of flight

Answer 282

 BaF2 used in the past; LSO/LYSO used in existing scanners; LaBr3 being tested
 3 characteristics
o Short rise and decay time
o High light output
o Good stopping power for 511 keV photons

Question 283

Why the axial spatial resolution is different in the central axis and off center axis? In PET?

Answer 283

 Due to depth of interaction effect
 Point spread function FWHM narrowest at mid-point between detectors (with discrete, FWHM ~ d/2 at centre, d near detector)

Question 284

Name causes of decreased spatial resolution in PET. Give five.

Answer 284

 Detector width
 Positron range
 Noncolinearity
 Depth of interaction
 Reconstruction filters

Question 285

What is the difference between in-plane and axial resolution in PET?

Answer 285

 2D PET: axial is better than in-plane (due to retractable septa)

 3D PET: resolution is equivalent in-plane and axial, provided detector width same in both directions

Question 286

For a PET system with a ring of 80 cm, what is the amount of blurring in mm?

Answer 286

Non-colinearity: R180° = 0.0022 x D = 0.176 cm = 1.76 mm

Rsys = SQRT(Rdet^2 + Rrange^2 + R180^2)

Question 287

What is the difference between 2D and 3D PET?

Answer 287

2D:
- +interslice septa; Lower sensitivity; Less scatter; Lower countrate; Easier reconstruction

3D:
- No interslice septa; higher sensitivity; higher scatter; higher countrate; More complex reconstruction

Question 288

Why is an absorptive collimator not used in PET (2 lines)

Answer 288

 PET relies upon electronic collimation to obtain directional information from non-absorptively collimated pairs of annihilation photons

 Use of absorptive collimation would prevent many useful detector pairings and decrease sensitivity

Question 289

Question on definitions for pulse pile-up rejection, coincidence count loss and misplacement

Answer 289

Pulse pile-up rejection
o When pulses in amplifier are too close together, they are summed and if amplitude is outside of PHA window, they are rejected

o Can reduce by:
 Decreasing width of amplifier pulse (pulse shaping)
 Measure length of pulse: if don’t return to baseline in specificied time, reject

 Count loss rate
o Events not registered due to pulse pile up or dead time
 Misplacement
o With high count rates, can have mispositioning due to pulse pile up (e.g., between 2 point sources)

Question 290

5 factors affecting resolution in SPECT

Answer 290

 Intrinsic resolution of gamma camera
 Angular/linear sampling intervals
 Shape and cut-off frequency of reconstruction filter
 Photon energy
 Collimator

Question 291

What are 3 causes of misregistration on SPECT-CT? (3 points)

Answer 291

1. Respiratory motion
2. Sag of emission table
3. Patient motion between studies
4. Change in SPECT COR due to collimator weight

Question 292

other than mis-registration, what are 3 other artefacts in SPECT/CT?

Answer 292

 CT truncation artifact - truncation-due to the smaller field of view of the CT, inaccurate attenuation correction
 Beam hardening
 Partial volume averaging
 Noise - large patient, low dose setting

Question 293

Asked for minimum number projections in RBC SPECT study given 8mm hemangioma, 60cm cirumference, 7.5mm resolution of camera at 10cm, 360 degree acquisition; show math (Another: How many stops are required in a 360 acquisition to detect a 7.5mm hepatic lesion in a 200cm diameter child where the camera head is 10 cm from the child’s abdomen and the resolution of the camera is 15mm) (Yet another: How many steps SPECT are required when the patient is 10 cm away from of the camera head, but their circumference is 27 cm and there is a legion that measures 7.5 mm, and the FWHM is 8mm)

Answer 293

 Example 1
o FWHM = 7.5 mm @10cm
o Δr = FWHM/3 = 2.5 mm
o Circumference = πD = 60 cm
o # views = πD/Δr over 360° = 60 cm/0.25 cm = 240

Question 294

Define “ring artifacts” on SPECT - what to they look like and name 2 causes

Answer 294

Rings of decreased or increased activity
o Non-uniformity (concentric rings, decrease in intensity toward periphery)

o Centre of rotation offset (non-concentric, full circle near centre of FOV, partial circle in periphery)

Question 295

What causes a ring artifact, why is it more important in spect vs. planar imaging?

Answer 295

Non-uniformity and centre of rotation offset

o Even small variations in non-uniformities can cause major artifact in reconstructed images

Question 296

what’s the difference between ring artefact produced by non-uniformity and COR and why is non-uniformity significant in SPECT vs planar?

Answer 296

 Non-uniformity: concentric full rings
 Centre of rotation offset: non-concentric, full circle near centre of FOV, partial circle in periphery
o Even small variations in non-uniformities can cause major artifact in reconstructed images

Question 297

They showed a transaxial picture of a brain? was terrible quality. then a second one which was blurred and a third one which was most blurry. Adjacent, they had another image showing point source that went to a half round circle. What is the difference between non-uniformity artifact and center of rotation artifact? Questions where: what is this artifact (COR) and how often is the QC done for this (weekly)?

Answer 297

• Centre of rotation offset: non-concentric, full circle near centre of FOV, partial circle in periphery
o QC weekly

Question 298

In addition to the usual QC procedures for gamma cameras, what are 2 additional QC procedures that are required for a camera capable of SPECT?

Answer 298

 Tomographic uniformity - High count flood-field uniformity test

 COR alignment

Question 299

Non-uniformity limit for SPECT

Answer 299

 <1%

Question 300

Why is uniformity more important for SPECT than planar imaging? What is an acceptable nonuniformity for SPECT? [French: Why is uniformity more important in PET than in SPECT?]

Answer 300

 Even small variations in non-uniformities can cause major artifact in reconstructed images

 <1%

Question 301

What is the integral uniformity limit accepted for SPECT images?

Answer 301

 <1%

Question 302

What is the daily QUALITY CONTROL TESTS FOR PET SCANNER, describe one technique. Describe what happens when one detector is not functioning. List 2 other weekly/monthly QC procedures for PET. NOTE is specifically mentioned PET NOT PET/CT

Answer 302

 Daily:
o Physical inspection
o Blank scan
       Full system initialization
       Baseline collection
       Calibrating PMT gains
       Energy test and analysis
       Timing test
       Emission collection and analysis
       Visual inspection of 2-D sinograms

 Two other weekly/monthly QC procedures for PET
o Tomographic uniformity: weekly
o Sensitivity: monthly (EANM)
o Normalization: annually
o Well-counter calibration: annually

Question 303

Artifacts in FDG-PET can be subdivided into hardware, acquisition, and processing varieties. What is the most common hardware-type artifact and what does it look like.

Answer 303

 Hardware:

 The most common hardware defect is block detector failure. Its appearance depends on the loss of sensitivity and whether it is a single or multiple blocks that are affected. Overall there is a loss of sensitivity (4-5% decrease in SUV for one block 100%, up to 18% for 2 that are coincident of each other). The appearance is also dependant on the geometric position of the two detectors, however if seen the appearance is of a cold stripe following the fan angle of the defective detector(s).

Question 304

Name 4 methods for respiratory gating? What are 2 artifacts associated with respiratory motion?

Answer 304

 Pressure sensor elastic belt around abdomen
 Spirometer measuring flow of respired air
 Nasal thermistor
 Infrared stereovision system tracking motion of thoracic markers

 Artifacts:
o Misregistration
o Image blurring

Question 305

What is the recovery coefficient, what is its value, what is the importance of the voxel in nuclear medicine?

Answer 305

 RC = Measured peak activity concentration / true activity concentration
 Linear sampling interval sets voxel size
 Too small voxel -> low counting statistics/voxel and ↑ noise
 Too large voxel -> partial volume averaging

Question 306

Define partial volume effect. Why is partial volume effect in whole body PET imaging more significant than in SPECT?

Answer 306

 Partial volume effect = incorrect estimation of activity concentration due to limited resolution of imaging system

o For small (<2 x FWHM) hot object, activity underestimated
o For small (<2 x FWHM) cold object, activity overestimated
 In PET quantitation of activity (i.e., SUVmax) more often used to follow-up lesions

Question 307

SUV and things that affect it.

Answer 307

 SUV = standardized uptake value = mean activity in ROI (MBq/ml) / (injected dose (MBq) / body weight (g))

 Factors:
o Size of ROI
o Injected dose
o Body weight
o Serum insulin
o Uptake time

Question 308

List 6 things that can cause a false positive finding on PET in a patient with lymphoma.

Answer 308

False positive in lymphoma
o Inflammation/infection
o Granulomatous disease, eg sarcoidosis
o Brown fat
o Post-radiation changes
o Post-operative changes
o Marrow hyperplasia with bone marrow supportive therapy (e.g., G-CSF)

Question 309

What is the effect on SUV of obesity? How would you adjust SUV calculations in an obese patient to be more realistic?

Answer 309

 SUV = mean activity in ROI (MBq/ml) / (injected dose (MBq) / body weight (g))
 Obesity not only ↑ SUV by ↑ body weight, but also, because little FDG in adipose tissue, relatively higher accumulation in lean body mass
 Can use BSA or LBM as weight-indepdent indices (replacing weight above)

Question 310

6 methodological factors that can change SUV in PET

Answer 310

 Dose of FDG
 Interstitial injection
 Uptake period
 Reconstruction matrix size, algorithm and filtering
 Size of ROI
 Attenuation correction

Question 311

Four advantages (or disadvantages) of iterative reconstruction algorithm.

Answer 311

Advantages:
 More quantitative
 Fewer reconstruction artifacts (streak, aliasing)
 More options for data corrections (scatter, attenuation, motion)
 Multiple methods for reconstruction

Disadvantages
 More computationally intensive
 Increased noise after too many iterations
 Non-linear
 Can get inferior image with poor model choice

Question 312

Name two types of iterative reconstruction algorithms.

Answer 312

 MLEM: maximum likelihood expectation maximization

 OSEM: ordered subset expectation maximization

Question 313

What does OSEM stand for? How is it better than MLEM? Name one disadvantage of MLEM compared to MAP algorithms.

Answer 313

 OSEM: ordered subset expectation maximization
o Smaller # of projections -> processing time much faster

 MLEM vs. MAP
o MLEM at high iterations emphasizes noise

 Guaranteed convergence
o MAP produces smoother solution

 Converges faster, but computationally difficult

Question 314

Asked to look at a set of photocopied images of a SPECT phantom. Set A has increased counts in periphery and set B is more homogeneous. What changed? Attenuation correction. What are two SOFTWARE methods of doing this in the clinic.

Answer 314

 Two software methods:
o Chang’s multiplicative with broad-beam coefficient
o Chang’s iterative method

Question 315

Two images, and you are supposed to recognize that one has been attenuation corrected. Carry on to describe two types of attenuation correction and briefly describe them

Answer 315

 Changs multiplicative and iterative methods,

multiplicative-using an idealized image or the non-corrected image, assume standard linear attenuation coefficient and calculate an ACF for each point on the matrix and apply (good for homogeneous structures);

iterative-obtain the corrected image as previous, forward project, subtract these from the acquired projections and FBP to produce the error image, apply the ACFs to the noncorrected and the error image and add together.

 Monte-Carlo method-mathematically model the attenuation at each point in the matrix.

 CT attenuation correction or transmission rod source attenuation correction-attenuation map is produced by calculating the projection profiles of attenuation using a blank image and a image of the patient, this it FBP to form the map which can be applied to Changs methods or more commonly to iterative recon methods.

Question 316

Two sealed tracers for PET attenuation correction:

Answer 316

 Ge-68, Cs-137

Question 317

Name four types of attenuation correction in PET and briefly describe

Answer 317

 68Ge rod source: pre-, post- or simultaneous transmission scan

 137Cs rod source: pre-, post- or simultaneous transmission scan

 Transmission CT: pre- or post-scan
o Scale using bilinear method to equivalent attenuation for 511 keV

 Chang method: assume uniform attenuation for attenuation correction factor

Question 318

Three types of attenuation correction for PET and briefly describe advantages and disadvantages of each.

Answer 318

CT transmission map
o ADV: rapid acquisition,high photon flux
o DISADV: discrepancy in energies, radiation dose

 Rod Source transmission map
o ADV: longer acquisition time, cheaper, closer energies
o DISADV: low photon flux, high contrast

 Chang Method
o ADV: fastest, cheapest
o DISADV: assumes uniform attenuation

Question 319

Differences between attenuation in SPECT and PET images.

Answer 319

 In SPECT, source to detector distance is important

 Tissue attenuation at SPECT energies, has large component contributed by photoelectric, vs. Compton for 511 keV annihilation photons for PET

 PET more susceptible to attenuation artifact

Question 320

Three methods of scatter correction in SPECT.

Answer 320

 Energy window methods
 First order Chang multiplicative with broad beam geometry
 Convolution subtraction: spatial analysis method based on the line spread function

Question 321

Define beam hardening on CT & give 2 consequences of beam hardening

Answer 321

 Selective absorption of low energy X-rays in highly attenuating materials results in increased average energy of transmitted beam

 Consequences:
o Interfere with attenuation correction in SPECT
o Artifacts like cupping or streak

Question 322

Give an example of a smoothing kernel (3 x 3 matrix with central value of 4). What is special about a Laplace filter?

Answer 322

 1,2,1
 2,4,2
 1,2,1

 Laplace: edge detection filter, identifies zero-crossing of second derivative

Question 323

A set of 7 numbers (3,4,5,6,6,8 or something), and give the mean, median and mode. Define each. (Define mean, median, and mode. Calculate mean, median, mode for the series 1,2,4,5,6,6,7)

Answer 323

Mean = average

Median = Median: middle value in ordered set, if odd number; mean of middle two in ordered set if even

Mode = Most commonly occurring value (may have multimodal sets, if more than 2 modes)

Question 324

describe continuous data and give 2 examples

Answer 324

 Continuous data can have any value within a certain range
o Weight
o Height

Question 325

describe discrete data and give 1 example

Answer 325

 Discrete data can only have certain values over a range

o Population

Question 326

What is the definition of power of a study?

Answer 326

 Probability that a statistical test will reject the null hypothesis when the null hypothesis is false

Question 327

Questions on ROC and MTF:

Answer 327

 MTF is the discrete Fourier transform of the line spread function

 ROC: TP fraction (Sn) vs. FP fraction (1-Sp)
 ROC: TP fraction (Sn) vs. FP fraction (1-Sp)
 AUC of ROC = accuracy

Question 328

describe how to construct a ROC curve

Answer 328

 Plot the sensitivity (True positive rate, y-axis) vs. 1-specificity (True negative rate, x-axis) for a series of experiments of a test with different cutoff values. The one that deviates most from the straight line represents the most accurate test.

Question 329

Define Bayes Theorem

Answer 329

 Bayes theorem states that the probability of theorem given new data (posterior prob)=(prob of the new data given the hypothesis (conditional prob)*probability of the hypothesis being true before the new information (prior prob)/prob of seeing that data (marginal prob)

Question 330

using TP, FP, TN, FN define: sensitivity, specificity, PPV, NPV, accuracy, true positive fraction

Answer 330

 Sensitivity (= true positive fraction) = TP / TP + FN
 Specificity = TN / FP + TN
 False positive fraction = 1-specificity
 TPF vs. FPF are the axis of the ROC
 PPV = TP / TP + FP
 NPV = TN / FN + TN
 Accuracy = TP + TN / TP + TN + FP + FN
 Additional derived rates:
 False positive rate = FP / TN + FP
 False negative rate = FN / TP + FN

Question 331

What does a p>0.05 indicate

Answer 331

P value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed, if the null hypothesis is true
 At a significance level (alpha) of 0.05, a calculated p value >0.05 would not be considered significant, and therefore the null hypothesis would not be rejected

Question 332

For a given number of ___ counts in a single pixel, what is the signal to noise ratio for that pixel?

Answer 332

N / SQR N

Question 333

Calculate the minimal detectable activity (MDA). Values given for: background count rate, confidence interval required (95%) and counting efficiency (mCi/cps).

Answer 333

MDA = 3*SQRT(Rb/t)

Rb = background count rate
t = counting time

Get cps, then divide cps by sensitivity of device to get activity

Question 334

Best statistical test for comparing proportions

Answer 334

Chi squared

Question 335

What is a positive likelihood ratio? What does it represent?

Answer 335

Likelihood-ratio positive = sensitivity / (1 − specificity) = Odds of disease after +ve test / Odds of disease before the test

 LR(+) the likelihood that +ve test result would be expected in patient with disease/the likelihood that +ve test would result in a patient without the disease.
 LR(-) the likelihood that –ve result result would be expected in patient with disease/-ve result in a patient without disease.

Question 336

If the likelihood ratio is 10, what does this mean for a positive test that detects lung cancer?

Answer 336

 Odds of lung cancer after +ve test is 10x higher than before test

Question 337

A worker has developed cancer and you are asked to advise the jury/courtroom about the probability of the patient developing cancer because of his work. Is there an equation you could use to define the probability that the cancer is work related?

Answer 337

 Probability of causation analysis to estimate a posteriori probability that radiation caused a particular cancer
o PC = (excess cancer rate due to radiation) / (excess cancer rate due to radiation + baseline risk) x 100%

Question 338

Be able to calculate % uncertainty – was given an EF calculation and also asked to calculate the standard deviation.

Answer 338

EF = [(EDC – bk) – (ESC – bk)] / [EDC - bk]

%error: SEE PAGE 196

Question 339

What is QALY? List 4 ways to monitor health outcome? What is the justifiable cost for QALY?

Answer 339

 QALY = quality adjusted life year = 1 year of life x utlity value (utility value = 0 for death, 1 for perfect health)
 4 ways
o Mortality
o Morbidity
o Disability adjusted life year (DALY) = years of life lost + years lived with disability
o Health-adjusted life expectancy (HALE) = average number of years that an individual is expected to live in a healthy state
 No clear-cut threshold, but values like $100,000/QALY have been suggested for advanced economies

Question 340

Calculate effective half life of Tc-99m tracer giving varied excretions (sum of the excretion is about 50% at 5 hours)

Answer 340

Teff = TpTb/(Tb+Tp) = 2.7h

Question 341

Define the term effective half life

Answer 341

 Teff = time for initial administered dose to be reduced to ½ of original by both physical decay and biological elimination

Question 342

Describe in vivo neutron activation analysis.

Answer 342

 Identifies the abundance of specific elements by distinct gamma ray spectra emitted after neutron activation
 Immediate or concurrent measurement for reactions with short decay half lives (prompt gamma)
 Longer lived products analyzed by delayed gamma

Question 343

Five currently used methods for labelling red blood cells and their labelling efficiency

Answer 343

 in vitro (Ultratag) - 98 %
 in vitro - 95%
 in vivtro - 90 - 95 %
 in vivo - 70 - 80 %
 51Cr labeling - 90%
 59Fe labeling
 111-In-oxine
 14C-glycine

Question 344

What is the most commonly employed method of RBC labeling and what is its labeling efficiency? What are 3 drugs which can interfere with labeling efficiency by the in vivo method?

Answer 344

 Ultratag kit >98%

 In vivo interference:
o Heparin
o Doxorubicin
o Digoxin
o hydralazine
o iodinated contrast media
o penicillin

Question 345

Causes of poor RBC labeling:

Answer 345

1. Heparinized patient - Complexes with pertechnetate leading to renal excretion
2. Chemotherapy - disrupts RBC membrane
3. Injection through iv - Adherence to wall of iv
4. Generator ingrowth time > 24 hours - Presence of excessive Tc99 from decay of Tc99m
5. Decreased hematocrit - Tc-99m is reduced outside the RBC

Question 346

Three ways of labeling RBC’s. Briefly describe each method. Name an advantage, a disadvantage and the efficiency of each method

Answer 346

1. In vivo:
    Inject SnPYP IV
    Wait 20 min
    Inject TcO4- IV
   Advantage = No handling of blood products
   Disadvantage = lowest labelling efficiency (75-90%)
2. Modified in vivo/in-vitro
    Inject SnPYP IV
    Wait 20 min
    Withdraw blood into syringe containing TcO4-
    Wait 10 min
    Reinject
   Advantage = Higher labeling efficiency than in vivo (85-95%) without need to separate blood from patient
   Disadvantage = Suboptimal labeling efficiency
3. In vitro
    Incubate blood with Sn citrate 5 min
    Add sodium hypochlorite, then ACD
    Add TcO4- 20 min
    Assess purity, reinject IV
   Advantage = Highest labeling efficiency (>97-98%)
   Disadvantage=Most handling of blood products

Question 347

In RBC labeling with pertechnetate:
a) Name two reducing agents

b) What happens to Sn once it is used to reduce pertechnetate?
c) Which part of the RBC does pertechnetate bind to?
d) What is the mechanism of entry of pertechnetate in the RBC?

Answer 347

a) Stannous citrate, stannous gluceptate, stannous pyrophosphate
b) Sn2+ is oxidized in the reaction (redox reaction)
c) 80% β subunit of hemoglobin, 20% heme directly
d) Enters via the bicarbonate-chloride anion exchanger (band-3 protein or Anion exchange 1)

Question 348

5 assumptions in assessing blood volume

Answer 348

 Small enough volume to not affect blood volume
 Remain within vascular space
 Even distribution/uniformly mixed
 In steady state equilibrium at time of measurement
 Stable, not metabolized

Question 349

Want to design a new tracer for blood volume measurements using dilution? 3 properties it was to have (3 points)

Answer 349

 Volume of tracer sufficiently small to not alter the volume to be measured
 Ideally remains within space of interest
 Easily measurable quantitatively

Question 350

Most popular label for red cell survival studies. If red cell survival is normal (mean 120 days) what is half-time value for this study? Why is there a difference? 3 locations of measurement if associated sequestration study

Answer 350

 51Cr-EDTA
 Half time = 60 days
 Difference from 1% elution/day of 51Cr-EDTA from RBC
 Locations of measurement
o Liver
o Precordium
o Spleen

Question 351

Problem with chromium 51 in RBC labeling.

Answer 351

 Problem: not stable
o early loss from damage
o 1% elution/day after
 Eγ = 320 keV (9%)
 T½ = 30 d
 Labeling efficiency: 80-90%

Question 352

What is the normal RBC survival half time on Cr-51 labelled RBC survival test? This is different from the actual RBC survival half time - explain.

Answer 352

 Normal RBC survival: 90-120 days
 Theoretical half-life of RBC labeled with Cr-51: 50-60 days

 Measured half-life of RBC labeled with Cr-51: 25-35 days

 Difference is due to:
o 1% elution of Cr-51 from tagged RBC’s per day
o RBC damage during labeling
o Poor labeling

Question 353

4 causes of decreased RBC survival or half life in survival study

Answer 353

 Intracorpuscular defects
o Spherocytosis
o Sickle cell disease

 Extracorpuscular defects
o Autoimmune hemolytic anemia
o Disseminated intravascular coagulation

Question 354

Define f-cell ratio. What range exists for this quantity in the literature?

Answer 354

 F- cell ratio: ratio of whole body hematocrit to venous hematocrit
 Varies, anywhere from 0.82-1.0

Question 355

A 4 year old weights 17 kg and with surface area of 0.71 m2, calculate theoretical value of (1) urinary bladder capacity; (2) dose of Lasix; (3) dose of captopril; (4) GFR:

Answer 355

 Urinary bladder capacity: (age+2) x 30 ml = 180 ml
 Dose of lasix: 1mg/kg
 Dose of captopril: 1 mg/kg max of 25 mg

 Adult levels reached by 6 mo-1y, so:
o GFR = 100-120 ml/min/1.73 m2 x 0.71 m2 ~49 ml/min

Question 356

Explain the method of GFR determination using the monoexponential, 2 blood sample technique

Answer 356

 Use detectable GFR agent in IV bolus
 Sample plasma at 2 time points
 Estimate GFR from plasma clearance by fitting values to monoexponential curve (P(t) = P(0) e-λt)
 GFR ~ plasma clearance = Dose/(Area under curve)

 A monoexponential method implies a single compartment model, the solution to which is an exponential decay in tracer concentration in plasma
 With 2 data points, we can obtain a curve-fit of the exponential curve with a single time constant, which then allows determination of the AUC and plasma clearance rate

Question 357

DTPA with excess pertechnetate – impact on quantitative GFR.

Answer 357

 TcO4- cleared much slower than DTPA; so will underestimate plasma clearance and therefore GFR

Question 358

How to do C-14 breath test

Answer 358

 Swallow capsule intact
 Wait 10 min
 Exhale into Mylar balloon
 Add to vial containing hyamine and ethanol with phenolphthalein pH
 If solution turns pink, adequate collection (indicates pH drop)
 Add liquid scintillation cocktail
 Read on liquid scintillation counter
 >200 dpm is positive

Question 359

In Schilling’s test, why 0.5 μg B12 is used?

Answer 359

 Don’t want to saturate the distal ileal receptors and cause non-IF mediated uptake

Question 360

What are the neurological symptoms of B12 deficiency?

Answer 360

o Posterior column dysfunction (subacute combined degeneration of spinal cord)
loss of position and vibratory sense
o Dementia
o Peripheral neuropathy
o Weakness and ataxia

Question 361

What two biochemicals can be measured in urine or blood to confirm B12 deficiency?

Answer 361

o ↑ homocysteine & methylmalonic acid levels in blood and urine

Question 362

Briefly describe the pathophysiology of B12 deficiency in the following conditions, naming the involved transport protein or receptor protein:

Answer 362

o Vitamin B12 absorption:
– Terminal ileum unable to absorb (↓cubam receptor)
– Ingested B12 is released from protein by digestive enzymes (gastric acid & pepsin)
– B12 binds to R protein in stomach (R protein found in gastric, biliary & salivary secretions)
– Pancreatic enzymes degrade B12-R & facilitate binding of B12 to IF in the presence of alkaline pH
– IF is produced by parietal cells in the fundus & body of the stomach
– B12 –IF is absorbed by the terminal ileum
– B12 enters serum bound to transcobalamin-I (75%) & transcobalamin-II (25%)

o Zollinger-Ellison syndrome:
– Low intestinal pH interferes with release of B12 from B12-haptocorrin complex
– Results in low intestinal pH & this interferes with release of B12-R protein and binding to IF

o Crohn’s:
– Inflammation ↓cubam receptor in terminal ileum

o Pancreatic insufficiency:
– ↓ protease in bowel to cleave B12-haptocorrin complex for intrinsic factor to bind
– impaired protease release of B12-R protein to bind to IF

o Cobalamin deficiency:
– In chronic deficiency, ↓cubam receptor in terminal ileum
– chronic B12 deficiency leads to alteration in small bowel mucosa, ie less IF-Vitamin B12 receptors in terminal ileum

o Atrophic gastritis (pernicious anemia):
– ↓ production of intrinsic factor
– impaired gastric release of food bound B12 and decreased production of IF

Question 363

Name the activity and mass of B12 given for the shilling’s test.

Answer 363

o 0.5 μCi 57Co-cobalamin in <1 μg

o 0.5 uCi (18.5 KBq) Co-57 labeled B12 not exceeding 1 ug

Question 364

When do you get the maximum urine excretion of B12?

Answer 364

o 8-12h (Henkin)

Question 365

What are 3 causes of falsely low B12 measurement on shilling’s test?

Answer 365

o Incomplete urine collection
o Renal failure
o Chronic B12 deficiency

Question 366

Shilling test questions (these were on the basic sciences section!) Give the maximum radioactivity dose, the flushing dose, indicate why to collect urine pre-study. When is the maximal urine excretion?

Answer 366

 0.5 μCi 57Co-cobalamin in <1 μg
 Flushing dose: 1 mg B12 IM
 Pre-study urine (12h before): to rule out prior radioisotope procedure
 Maximal: ~8h
 Normal >9%
 Abnormal <7%

Question 367

Five pathophysiologic causes of vitamin B12 deficiency and disease states which can cause this.

Answer 367

 Food: B12-deficient intake
 Stomach: pernicious (lack of intrinsic factor), congenital defect in intrinsic factor, partial or gastrectomy, atrophic gastritis
 Pancreas: chronic pancreatitis (insufficient proteolytic enzymes to cleave B12-haptocorrin complex)
 Jejunum: bacterial overgrowth, parasites (competitive consumption) and sprue
 Ileum: ileum resection, Crohn’s disease, chronic B12 deficiency (↓cubam receptor)

Question 368

Basic questions on B12 test preparation

Answer 368

 Check serum B12, folate, homocysteine and methylmalonic acid levels
 Overnight fast
 No recent B12 treatment
 Confirm no prior Nuclear medicine study
 Collect urine 12h before to ensure no other radioisotope

Question 369

75SeHCAT Breath test!!!!! how is tracer administered, how is it measured? THOSE bastards

Answer 369

 Oral capsule (10 μCi = 370 kBq)
 Uncollimated gamma camera
o Image head to thigh, 1-3 h after ingestion
o Repeat scan at 7 days
 Retention >15% normal
 Retention <10% abnormal, suggest bile acid malabsorption

Question 370

Very brutal question on bone kinetics using MDP – name two tests for quantitation. Another part – what is the typical whole body retention of MDP at 24 hours?

Answer 370

 2 tests:
o 24h whole body retention (whole body counting at baseline and 24 hours; if no whole body counter, can do 24h urine collection, confirmed with 51Cr-EDTA)

o Modified Brenner method (gamma camera based, using adductor ROI to track soft tissue curve)

 Typical retention ~30% @24h (assuming normal GFR in adult)

 Tracers: 99mTc-MDP (bone tracer) and 51Cr-EDTA (GFR tracer)

Question 371

What assumptions are made with regard to the tracer in tracer kinetic studies.

Answer 371

 Tracer properties
o No isotope effect
o Trace quantity, to not perturb system
high specific activity
o Mimics biochemical or physiologic process/compartment
o Stable, or metabolized like endogeneous biochemical

 System:
o Steady state
o Instantaneous and complete mixing

Question 372

Define compartment as used in tracer kinetic studies.

Answer 372

 Volume or space which behaves as a single, homogeneous, well-mixed distinct component of the overall biological system, which can be physical space, distinct chemical form or pharmacologic state

Question 373

Using bone density measurement as an example, define regression to the mean:

Answer 373

 Given serial measurements of BMD in an individual, actual measurements fluctuate around a “mean value”
 For a single measurement, if the BMD is measured above the mean, there is a high probability a subsequent measurement will show a lower BMD that reflects the regression to the mean.

Question 374

variables to assess in acceptance testing of DEXA machines

Answer 374

 Leakage radiation and scatter radiation exposure rates (controlled area <0.4 mSv/wk, uncontrolled <20 μSv/wk)
 HVL determination with Al sheets to assess beam quality
 Entrance skin exposure using dosimeter/chamber
 Precision and accuracy with step-wedge phantom
 X-ray tube voltage and current determination

Question 375

At what 4 points in an ISCD certified institution should a technologist should their precision be assessed?

Answer 375

1. One complete precision assessment after basic scanning skills have been learned
2. Precision assessment after having scanned at least 100 patients
3. Repeat precision assessment if a new DXA system is installed
4. Repeat precision assessment if a technologist’s skill level has changed

Question 376

You purchase a new DXA with 0.002 g/cm^2. List 4 quality control procedures you would perform and the least significant change you would accept.

Answer 376

P– precision – long term precision error, coefficient of variation
C – constancy – phantom measured every day, values are plotted on Shewart chart or Cusum mask.
L – linearity – samples of bone ashes of increasing quantity are measured and plotted vs measured BMD
A – accuracy – measure a phantom whose precise composition is known (usually bone ashes).
G – geometry – check photopeak of X-ray source, check for beam distortion or beam hardening

Least significant change should be determined from precision error by precision assessment, not from manufacturer’s specifications; ISCD 2007 position statement:
o Lumbar spine: 5.3%
o Total hip: 5.0%
o Femoral neck: 6.9%

Question 377

List 3 things to include in a quality control program for a DEXA facility

Answer 377

 Calibration (daily)
 Phantom scanning (weekly)
 Precision assessment

Question 378

Define T and Z-scores in relation to children

Answer 378

 T-scores not used for children
 Z-score = #SD away from age and sex matched normal population
 Low bone mineral content/density is Z-score <= -2.0
 Osteoporosis diagnosed on the basis of both significant fracture and Z<=-2.0

Question 379

Define T-score and Z-score. How do you calculate least significant change?

Answer 379

 T-score = (BMDpatient – BMDyoung normal female reference)/SDyoung normal female reference

 Z-score = (BMDpatient – BMDage-matched reference)/SDage-matched reference

 LSC = RMS-SD x 2.77 (i.e., 95% confidence interval)
 Root mean sqaure-SD determined from scanning 15 patients 3x each or 30 patient 2x each

Question 380

List 8 causes of abnormal results on BMD

Answer 380

Falsely increased:
o Compression fracture
o Degenerative changes – osteophytes
o Severe aortic calcification
o Severe scoliosis
o Blastic metastases
o Surgical hardware
o Overlying objects
o IV / oral contrast

Falsely decreased:
o Previous laminectomy
o Lytic lesions
o Improper technique (typically increases but can decrease with hip positioning)

Question 381

List the 3 most common causes of osteoporosis in men other than hyperthyroidism, malabsorption

Answer 381

 Alcohol, smoking, steroids, hypogonadism

Question 382

What are the types of osteoporosis and the causes of Type I?

Answer 382

• Osteopenia: decrease in mass of normal bone but no increase in risk or incidence of fragility fracture.
• Osteoporosis: decrease in mass of normal bone (mineral and matrix) which results in compromised bone strength predisposing to an increased risk of fragility fracture.
• Primary Type I (Post menopausal) = ↓ estrogen secretion →↑IL1, 6, TNFa → ↑osteoblast/clast → ↑resorption,

• Primary Type II (Senile osteoporosis) – typically after age 70, women 2x as affected as men.
o Thought to be related to increased parathyroid function or VitD resistance / deficiency

Question 383

Give 5 indications for doing a bone densitometry.

Answer 383

All menopausal women aged > 65 yo
Premenopausal women > 40 yo with at least one fragility fracture.
Men > 70 y.
Patients followed for osteoporosis
Drugs predisposing for osteoporosis (steroids, dilantin, barbiturates, alcohol, tobacco etc)
Disease predisposing for osteoporosis (Cushings, hyperthyroid, hypogonadism, IBD, celiac disease)