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PET Exam > PET exam > Flashcards

PET exam Flashcards

1
Q

Types of disintegration/transformations (decay)

A

(1) alpha decay
(2) beta decay
(3) electron capture
(4) isomeric transition

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2
Q

Positron Emission

A

beta transformation:
emission of positively charged electron (positron) from nucleus of radioactive atom

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3
Q

Types Beta Decay

A

1 Positron Emission
2 Simple B Decay

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4
Q

Types of Positron Decay

A

1 Simple - daughter is at ground state after decay
» Only ionizing radiation is positron emission

2 Daughter is at excited state after the decay
» Prompt emission of gamma ray after positron emission

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5
Q

Gamma Ray

A

photon of electromagnetic radiation from excited nucleus

y ray

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6
Q

Photon

A

the smallest entity of energy emitted in the form of electromagnetic radiation and is sometimes referred to as a quantum of energy

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7
Q

Important examples of positron emitters with simple positron decay used in the PET laboratories are…

A

carbon-11 (11C), oxygen-15 (15O) and fluorine-18 (18F)

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8
Q

Important examples of positron emitters with decay leaving an excited daughter

A

copper-60 (60Cu)
gallium-66 (66Ga)
iodine-124 (124I)

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9
Q

Disintegrations of a particular radionuclide generally result in…

A

the emission of one or more distinctive types of ionizing radiation

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10
Q

unit of energy commonly used to denote particle and photon energies in atomic physics

A

electron volt (eV)
kiloelectron volt = 1 keV = 1,000 eV, and
megaelectron volt = 1 MeV = 1,000,000 eV

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11
Q

What is the average positron energy for a particular positron-emitting radionuclide?

A

about 40% of its maximum energy

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12
Q

Positron interactions with matter

A
  1. dislodging electrons from atoms to form ions (ionization)
  2. exciting atomic electrons to higher energy levels (excitation)
  3. causing vibrations of molecules (excitation)
  4. breaking molecular bonds (excitation), and
  5. producing electromagnetic radiation subsequent to a sudden change of direction in the positron’s path (bremstrahlung)
       >> (1) ionization, (2) excitation and (3) bremstrahlung
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13
Q

What is the level of energy emitted by a positron from a radionuclide

A

continuum of kinetic energies…
from essentially zero kinetic energy to a maximum energy that is uniquely characteristic for the radionuclide

> > less than 10% of the emitted positrons from a given radionuclide will travel as far as one-half of the range before dissipating their kinetic energies

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14
Q

Annihilation

A

After an emitted positron has dissipated its kinetic energy, it very quickly combines with an ordinary electron and the two particles undergo mutual annihilation.

  • rest mass of each particle is converted to electromagnetic energy
  • The two photons are emitted in opposite directions to conserve momentum
  • The simultaneous emission of the two 511 keV photons in opposite directions serves as the foundation of PET detection
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15
Q

Another name for radioactive decay

A

Disintegration rate

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16
Q

What does the disintegration rate tell us

A

Used to indicate the “radioactivity” of a sample and it is termed the activity

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17
Q

Traditional unit of activity in radioactive decay

A

curie (Ci)

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18
Q

curie (Ci)

A

the amount of radioactive material having a disintegration rate of
3.70x1010 (37 billion) disintegrations per second

> > millicurie = mCi = 0.001 Ci,
microcurie = uCi = 0.000001 Ci

19
Q

What does activity denote?

A

only the rate of disintegration;
provides no information concerning the kind of radiation emitted

20
Q

Half-life

A

Time necessary for one-half of the radioactive atoms of a sample to
decay

21
Q

Half-Value Layer (HVL)

A

Amount of material (often expressed as the thickness) required to reduce the transmitted photon radiation to one-half of the incident value

> > Often used to express the attenuation/absorption properties of a material for photons

22
Q

Dose equivalent

A

The expression of biological damage caused by “ionizing radiation”

> > Often referred to as “dose”
Unit = rem

23
Q

Ionizing radiation examples

A

Gamma rays
x-rays
beta particles

24
Q

What is the naturally occurring “background” radiation level

A

0.3 rem per year in the U.S.
(300 millirem)

25
Q

What levels of radiation are known to cause harm (considered large)?

A

“acute” doses of greater than 10 rem received over a short period of time

“chronic” doses incurred over a prolonged period, e.g., years, of greater than one hundred rem

26
Q

Known radiological effects on humans

A

elevated risk of cancer, cataracts, genetic effects, etc

27
Q

Opinions concerning the harm of relatively low radiation dose

A
  1. No threshold model
    » This concept says unit dose risk factors, e.g., % chance of harm per rem that are numerically the same as those that apply to much higher doses
    » Used by state & federal regulatory agencies
  2. Thresholds exist for most harmful effects but those are greater than the doses received by occupational radiation workers
  3. Hormesis
    » Low doses of ionizing radiation are actually beneficial
28
Q

Which model must we abide by concerning radiation dose levels?

A

The view of the regulatory agencies is based on the assumption that any amount of radiation exposure is potentially harmful

29
Q
  1. Who has authority of the use of the cyclotron-produced radioactive materials employed in the PET laboratories?
  2. Who additionally provides recommendations concerning dose limits for radiation workers?
  3. Who was it, historically?
A
  1. The NRC
  2. NCRP - The National Council on Radiation Protection and Measurements
  3. The state of Missouri
30
Q

The three classic methods for controlling external radiation exposure are:

A

(a) minimize time spent in a radiation field
(b) maximize distance from the source of radiation
(c) utilize shielding between you and the source

31
Q

Why does the relatively large annual radiation doses incurred by PET personnel occur?

A

(a) the emitted radiations are abundant and generally penetrating and
(b) large activities are often handled to compensate for the rapid decay occurring during the studies in which they’re used

32
Q

Why are doses due to internal contamination are not a primary concern in your work

A

Because of the short half-lives of the radionuclides that we use

33
Q

ALl

A

Maximum annual limits of intake specified by federal government
» represents the activity of a given radionuclide that, if ingested or inhaled by a person will result in the more limiting of

(a) 5 rem of effective whole body dose
or
(b) 50 rem to the “critical” organ

34
Q

Where is the “Emergency Procedures Involving Radioactive Material Contamination” notice posted?

A

In each PET laboratory

35
Q

What does the “Emergency Procedures Involving Radioactive Material Contamination” notice tell you?

A

The instructions address the clean up of a spill and personnel
decontamination

Also, each notice explains how to contact Radiation Safety for
assistance and who to notify

36
Q

Pneumatic lines

A

Used to transport very short-lived radiopharmaceuticals

37
Q

What happens if the carrier of the pneumatic lines is unable to arrive at their destination?

A

The cyclotron personnel should be immediately informed

38
Q

What happens if the wrong radiopharmaceutical is sent from the cyclotron?

A

Promptly notify the cyclotron (314-362-2261, 314-362-8393)
& Sally Schwarz (314-362-8426, pager # 314-490-3081)

39
Q

What happens when a patient will not remain motionless during PET imaging?

A

a family member or other accompanying individual should be asked to restrain the patient; it
should not be done by PET personnel

40
Q

body dosimeters

A

“optically stimulated luminescence”
(OSL)
» “Luxel” dosimeters
» very sensitive to ionizing radiation
» The minimum reported dose is one millirem (mrem)
» A measured dose less than one mrem is reported as “minimal” (M)

The reported doses for each body dosimeter are
(1) the deep dose (the calculated dose at a tissue depth of 1.0 cm)
(2) the shallow (or skin) dose
(3) the lens dose.

41
Q

ring dosimeters

A

“thermoluminescent” dosimeters
(TLD)

The doses for ring dosimeters are reported as shallow doses down to a minimum of 10mrem

Ring doses less than 10 mrem are reported as “minimal “ (M).

42
Q

(ALARA)

A

maintain personnel radiation doses as low as reasonably achievable
- all reported external doses are reviewed for unusually high levels by a member of the Radiation Safety Staff
- reports the investigations to a special subcommittee of our institutional Radiation Safety Committee

43
Q

relationship between distance and radiation

A

The exposure level varies inversely with the square of the distance from the source (the relationship applies for distances large compared to the physical dimensions of the source)

> > 4-fold reduction of the dose rate

44
Q

Shielding

A

pigs or lead containers used to transport cyclotron-produced materials should be sufficiently thick to reduce external levels to an acceptable value
» In addition, it is helpful to use a Lucite sleeve over a syringe, a so-called “beta shield”, to absorb energetic positrons

PET Exam (1 decks)

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