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nuclear med > week 1-2 > Flashcards

week 1-2 Flashcards

1
Q

most common radioisotope in NM

A

Tc-99m

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2
Q

half life of Tc-99m

A

6 hours

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3
Q

what type of radiation does Tc-99m emit

A

gamma ray

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4
Q

half life of I-131

A

8 days

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5
Q

what is I-131 used for

A

imaging and treatment of thyroid disorders and inoperable liver cancer

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6
Q

what type of radiation does I-131 emit

A

gamma and beta

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7
Q

what is Tc-99m used for

A

80% of the scans - bones, brain, cardiac, thyroid, lung, renal

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8
Q

types of gamma camera

A

single detector
multi detector

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9
Q

types of dual detector systems

A
  1. detectors fixed at 180deg apart
  2. detectors fixed at 90deg apart
  3. detectors at variable angle between 75 and 180deg
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10
Q

what is 90deg dual detector used for

A

cardiac imaging

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11
Q

what is 180deg dual detector used for

A

general SPECT
total body imaging

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12
Q

advantages of a dual detector system

A
  • improved resolution
  • cost effectiveness
  • faster patient throughput
  • space constraints
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13
Q

components of a gamma camera

A
  • collimator
  • sodium iodide crystal
  • photomultiplier tube
  • PHA circuit, discriminator, analyser circuits
  • computers for data processing and display
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14
Q

how does photomultiplier tube work

A
  • gamma photon enters the NaI scintillation crystal, gets converted to light photon and enters to PMT
  • PMT converts light photon into photoelectrons
  • localises the position where the gamma ray interacts in the crystal
  • match performance from tube to tub within a camera detector
  • reduced light barrier between tubes
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15
Q

types of collimators

A
  1. parallel-hole collimator
  2. converging collimator
  3. pin-hole collimator
  4. diverging collimator
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16
Q

what is the converging collimator used for

A

magnification

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17
Q

what is pin-hole collimator used for

A

magnification + inverted image

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18
Q

what is diverging collimator used for

A

minification

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19
Q

how does the diameter and length of collimator holes determine the field of view, sensitivity and spatial resolution

A
  • larger holes increase sensitivity but degrades resolution
  • shorter length increase fov and sensitivity but degrades spatial resolution
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20
Q

performance parameter of a gamma camera

A
  • spatial resolution
  • non-uniformity
  • count rate characteristics
  • energy resolution
  • sensitivity
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21
Q

what is spatial resolution

A
  • refers to the smallest separation between 2 radioactive point sources
  • dependent on intrinsic and collimator resolution
22
Q

what is intrinsic uniformity dependent on

A

PMT balance, crystal, electronics, imaged without collimator

23
Q

what is extrinsic uniformity dependent on

A

PMT balance, crystal, electronics, collimator integrity, imaged with collimator using flood source

24
Q

how are radiopharmaceuticals different from other drugs

A
  • require shielding
  • most given intravenously
  • short shelf-life
  • strength of every dose can be checked
  • given in very small amounts
  • purity of every dose can be checked
25
Q

what are the half lifes of radionuclides

A

therapeutic (alpha and beta) - days
diagnostic (gamma and positron) - minutes and hours

26
Q

how can the different types radioactivity be stopped

A

alpha - paper / hand
beta - aluminium / plastic / glass
gamma - lead / concrete
neutron - water

27
Q

ideal properties of radionuclide for diagnostic use

A
  • gamma ray emission only
  • gamma energy 100-250keV for imaging
  • physical half-life approx 1.5times duration of test
  • simple cheap production/ purification
  • versatile chemistry
28
Q

ideal properties of radionuclide for therapeutic use

A
  • pure beta minus or alpha emitter
  • particle energy suitable for purpose
  • physical half-life of a few days
  • simple cheap production/ purification
  • versatile chemistry
29
Q

types of localization

A
  1. compartmentalised
  2. passive diffusion
  3. filtration
  4. facilitated diffusion
  5. active transport
  6. phagocytosis
  7. cell sequestration
  8. capillary blockade
  9. ion exchange
  10. chemisorption
  11. cellular migration
30
Q

what is compartmentalised localisation

A

to put a radiotracer in a bounded space and distributed in an enclosed volume and sustaining the tracer for time enough to scan that bounded space

a. uniform dispersion

b. non-uniformities within the compartment
- areas of increased radiopharmaceutical concentration may reflect pathological changes in the tissue or organ
- areas of decreased radiopharmaceutical concentration is usually the outcome of blockage in the cavities

c. leakage from the compartment

d. movement within the compartment

31
Q

what is passive diffusion

A

comprises motion of molecules across the membrane

a. factors that affect mobility of molecules to move across membrane: pH, ionisation, size of molecule, lipid solubility

b. characteristics of passive diffusion
- concentration gradient is required
- fast at high concentration gradient and slow at low concentration gradient
- does not need any sort of input
- non-selective process because no carriers or receptors are included

32
Q

what is filtration

A

special case of diffusion involving transit of molecules through pores, or channels, driven by hydrostatic or osmotic pressure gradient

a. characteristics
- requires some sort of force or pressure gradient
- does not require the local input or other external energy
- no transporters, carriers, or other receptors involved, so filtration is non-selective, is not competitively inhibited by similar molecules, and is not subject to saturation

33
Q

what is facilitated diffusion

A

carrier-mediated transport across membrane
- carrier is utilised to carry the molecule across the membrane (selective carrier membrane)
- inhibited by the presence of similar molecules
- saturation can be achieved to maximum due to limited number carriers
- passive and involves a concentration gradient, external energy not employed

34
Q

types of impurity and how they can be detected

A
  1. radionuclidic - radioactivity measurement (dose calibrator)
  2. chemical - colorimetric
  3. radiochemical - thin later chromatography
35
Q

what is equivalent dose

A

parameter to accommodate the difference in biological effects of different radiation types

absorbed dose x weighting factor

36
Q

2 effects that radiation may cause to cells

A
  • deterministic effect
  • stochastic effect
37
Q

what is deterministic effect

A
  • effects are due to significant cell death
  • basis of radiotherapy where cancer cells are targeted
  • severity is directly proportional to exposure dose
  • threshold level exists
  • appropriate radiation protection mechanism and occupational exposure dose limits to be put in place to reduce this effect
38
Q

what is stochastic effect

A
  • effects are due to significant cell damage
  • probability of effect is directly proportional to exposure dose
  • no threshold level for these effects
  • long latent period between irradiation and occurrence of effect
39
Q

determinants of biological effects

A
  • rate of absorption
  • area exposed
  • variations in species and individual sensitivity
  • variations in cell sensitivity
40
Q

rank the tissue/organs in accordance to their sensitivity to radiation

A

low: muscle, joints, central nerves, fats
|
| skin, inntr-layer intestine, eyes
|
high: bone marrow, breast, lymph system, reproductive organs

41
Q

what is the dose limit of whole body for both radiation worker and public

A

radiation worker: 20mSv/year
pregnant staff: 2mSv/year for the remaining duration of pregnancy after declaration
public: 1mSv/year, excluding any medical exposure

42
Q

what is the dose limit for the extremities for both radiation workers and public

A

radiation workers: 500mSv/year
public: 50mSv/year

43
Q

what are the 3 basic principles of radiation protection

A

Shield (shielding the source)
Time (minimize time of exposure)
Distance (inverse square law)

44
Q

what is half-value layer (HVL)

A

thickness of any given material where 50% of the incident energy has been attenuated

45
Q

types of personal radiation monitors

A
  • film badge dosimeter
  • thermoluminescent dosimeter (TLD)
  • optically stimulated luminescence (OSL) dosimeter
  • electronic personal dosimeters
46
Q

3 most common types of radiation detector

A
  • gas detectors
  • scintillation counters
  • solid state detectors
47
Q

possible routes of entry of radionuclides

A
  • ingestion
  • inhalation
  • skin absorption
  • through cuts or wounds
48
Q

2 types of contamination that must be controlled

A
  • removable surface contamination
  • airborne contamination
49
Q

pregnant staff can continue working in radiological dpt as long as fetal dose is kept below

A

1mGy

50
Q

1mSv of fetal dose is equivalent to

A

~2mSv to abdomen

nuclear med (3 decks)

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