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AJT Physics > PHYSICS - Nucs > Flashcards

PHYSICS - Nucs Flashcards

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1
Q

Radiopharmaceutical definition

A

radio-isotope + pharmaceutical

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2
Q

Radionuclides definition

A

unstable radio-isotopes; decay to more stable form resulting in release of radiation

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3
Q

Mass number

A

A (for mAss); protons + neutrons

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4
Q

Atomic number

A

Z; protons

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5
Q

Isotopes

A

same number of protons

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6
Q

Isotones

A

same number of neutrons

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7
Q

Isomers

A

same number of protons and neutrons, different energy

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8
Q

Isobars

A

same mass number (A)

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9
Q

Gamma rays originate from…

A

nucleus (as opposed to x-rays which originate from orbital electron interactions)

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10
Q

1 mCi is how many MBq?

A

37 MBq; 1 Bq = 1 decay/second

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11
Q

SI units

A

Bq, Gy, and Sv (NOT Ci, rad, or rem)

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12
Q

Activity definition

A

decays per unit time

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13
Q

Specific activity definition

A

activity per unit mass; measured in Ci/g or Bq/g

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14
Q

Relationship between decay constant and time constant

A

inversely related; _ = 1 / _

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15
Q

Effect of a larger decay constant on half-life

A

shorter half life

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16
Q

Effective half-life should be…

A

longer than the examination time

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17
Q

Effective half-life relative to biological and physical half-life

A

effective half-life is always shorter than either the biological and physical half-life

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18
Q

Alpha decay

A

release of 2 protons + 2 neutrons (alpha particle)

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19
Q

What is a beta particle?

A

essentially an electron released from the nucleus; in beta-negative decay

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20
Q

Beta-minus decay

A

release of beta particle + anti-neutrino; N => P; new element formed

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21
Q

Example of beta-minus decay

A

Mo-99 => Tc-99m

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22
Q

Electron capture

A

orbital electron captured by nucleus; P => N; new element formed; always accompanied by characteristic x-ray release

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23
Q

Beta-positive decay

A

release of positron + neutrino; P => N; new element formed

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24
Q

Decay type(s) with neutron excess

A

beta-minus decay

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25
Q

Decay type(s) with proton excess

A

beta-positive decay, electron capture

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26
Q

Preferred decay type with proton excess and sufficient energy

A

beta-positive decay (positron emission)

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27
Q

Preferred decay type with proton excess and insufficient energy

A

electron capture

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28
Q

Excess energy after radioactive decay is released via…

A

internal conversion or isomeric transition

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29
Q

Decay type for Tc-99m => Tc-99

A

isomeric transition (remember the definition of isomers)

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30
Q

Isomeric transition

A

excess energy released as gamma photons

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31
Q

Internal conversion

A

excess energy transmitted to orbital electron which is ejected => orbital hole filling results in production of characteristic x-ray or Auger electron

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32
Q

Decay type(s) resulting in characteristic x-ray production

A

internal conversion, electron capture

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33
Q

Nuclear reactor production

A

production via bombardment with neutrons

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34
Q

Cyclotron production

A

production via bombardment with charged particles

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35
Q

Radionuclide production - products have neutron excess

A

neutron bombardment, nuclear fission; decay by beta-negative decay

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36
Q

Radionuclide production - products are neutron deficient

A

cyclotron; decay by electron capture or beta-positive decay

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37
Q

Radionuclide production - products are carrier-free

A

cyclotron, nuclear fission

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38
Q

Carrier-free definition

A

none of stable element accompanying products

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39
Q

Parent half-life is much greater than daughter half-life

A

secular equilibrium

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40
Q

Parent half-life is slightly greater than daughter half-life

A

transient equilibrium

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41
Q

How many daughter half-lives for daughter activity to equal parent activity in secular and transient equilibrium?

A

4 daughter half-lives for both (per Huda)

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42
Q

Equilibrium type for Mo-99 => Tc-99m

A

transient equilibrium

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43
Q

Ideal time to “milk” Mo-Tc generator

A

every 4 half-lives (24 hours or 1 day)

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44
Q

How many days until Molybdenum is used up in Mo-Tc generator?

A

5 days (or 1 week)

45
Q

Isotopes produced from a generator

A

Tc-99m, rubidium; generators are used to produce short-lived isotopes

46
Q

SPECT (acronym)

A

Single Photon Emission Computed Tomography

47
Q

Cardiac SPECT

A

L-mode, 180 degree arc (-45 RAO to +135 LPO), images sorted by phase of cardiac cycle using ECG to create cines, 64 x 64 matrix

48
Q

Causes of image degradation (PET)

A

positron travel, angle of photon emission, scatter and absorption, simultaneous separate events

49
Q

2-D PET

A

less sensitive, less scatter => reduced noise; fewer true events detected => longer study

50
Q

3-D PET

A

more sensitive; increased scatter and random events detected

51
Q

Time-of-flight systems (3-D PET) most improve image quality in…

A

obese patients

52
Q

Alternate names for gamma camera

A

scintillation camera, Anger camera

53
Q

Spatial information in planar/SPECT vs. PET

A

collimators in planar/SPECT, coincidence detection in PET

54
Q

Low-energy collimator radionuclides

A

Tc-99m, I-123, Xe-133, Tl-201

55
Q

Medium-energy collimator radionuclides

A

Ga-67, In-111

56
Q

High-energy collimator radionuclides

A

I-131

57
Q

Pinhole collimator

A

magnified and inverted image; FOV increases with distance between patient and collimator; magnification decreases with distance between the patient and collimator, and increases with distance between the collimator and detector

58
Q

Parallel hole collimator

A

no magnification; FOV does not change with distance

59
Q

Converging collimator

A

magnified image, FOV decreases with distance (CDD)

60
Q

Diverging collimator

A

minified image, FOV increases with distance (DID)

61
Q

Pinhole collimator - sensitivity and spatial resolution

A

low sensitivity, high spatial resolution; varies with pinhole size

62
Q

Parallel hole collimator - sensitivity and spatial resolution (distance)

A

spatial resolution decreases with increased distance; distance has no effect on sensitivity

63
Q

Parallel hole collimator - higher sensitivity (septa)

A

thinner septa, shorter septa, larger inter-spaces

64
Q

Parallel hole collimator - higher spatial resolution (septa)

A

longer septa, smaller inter-spaces, decreased distance

65
Q

Parallel hole collimator - decreased penetration (septa)

A

thicker septa, longer septa

66
Q

LEHR vs. LEAP collimators

A

LEHR has longer septa with smaller inter-spaces => decreased sensitivity, increased spatial resolution

67
Q

Effect of switching from a low energy to a high energy collimator

A

decreased penetration, decreased sensitivity, decreased resolution (all because of thicker septa)

68
Q

Effect of increased scintillator crystal thickness

A

increases sensitivity, decreased spatial resolution

69
Q

Light to electrical signal conversion component (gamma camera)

A

photomultiplier tubes (PMTs)

70
Q

Artifact: focal photopenic defect

A

single bad PMT

71
Q

Pile-up (gamma camera)

A

summation of two events occurring before integration time

72
Q

Pile-up increases with…

A

increased integration time, higher radionuclide activity level

73
Q

Normal SPECT matrix size (non-cardiac)

A

128 x 128; cardiac is 64 x 64

74
Q

Elliptical orbit of gamma camera (SPECT) improves…

A

spatial resolution

75
Q

SPECT improves ______ relative to planar imaging

A

contrast (by removing overlapping structures)

76
Q

How to: fix inhomogeneities (gamma camera)

A

pre-scan flood field used to adjust for inhomogeneities

77
Q

Downscatter

A

Compton scatter from higher energy radionuclide is picked up in photopeak window for subsequently administered lower energy radionuclide

78
Q

Effect of downscatter

A

decreased CNR

79
Q

How to: avoid downscatter

A

use lower energy radionuclides first

80
Q

Standard Uptake Value (SUV)

A

mean ROI activity / (administered activity / lean body weight)

81
Q

Diffusely decreased SUV values (PET)

A

high blood glucose

82
Q

Contrast is negatively affected by…

A

scatter and septal penetration

83
Q

Intrinsic resolution

A

performance of gamma camera without collimator

84
Q

Energy resolution

A

ability of an imaging system to distinguish between photon energies (to remove scatter)

85
Q

Spatial resolution - planar vs. SPECT

A

planar has better spatial resolution (always)

86
Q

Survey meters

A

gas-based detectors; in order of highest-to-lowest sensitivity: GM > proportional counter > ionization chamber

87
Q

Pancake probe

A

a.k.a. Geiger-Mueller counter; higher voltage applied across ionization chamber

88
Q

Cutie pie

A

a.k.a. ionization chamber; lower voltage applied across ionization chamber

89
Q

Dose calibrator

A

essentially an ionization chamber; quantifies radiation in clinical doses; must select type of radioisotope prior to measuring

90
Q

Well counter

A

NaI-lined lead tube; for detecting activity <1 uCi; saturates quickly; used for wipe test

91
Q

Geometric efficiency of well counter

A

very high (all gamma rays interact with NaI crystal)

92
Q

Thyroid probe

A

for calculating %RAIU; single NaI crystal, PMT, and a single hole collimator; no image created

93
Q

Attenuation correction is performed for which of planar, SPECT, and PET?

A

SPECT and PET (not planar)

94
Q

Attenuation of gamma rays in patient is dependent upon…

A

originating location in patient, size of patient, energy of gamma rays (lower energy => more attenuated)

95
Q

Scanning line source attenuation correction

A

attenuation map has low SNR; uses isotope with a long half-life (gadolinium)

96
Q

Defect on extrinsic uniformity QC, but not intrinsic uniformity QC

A

issue with collimator

97
Q

Order of “peaks” from a point source (left-to-right)

A

Compton scatter, Compton edge, backscatter, iodine escape peak

98
Q

Artifact: star artifact (SPECT)

A

septal penetration

99
Q

Artifact: diffusely decreased counts (SPECT)

A

incorrect energy window (for type of isotope and study)

100
Q

Artifact: 2 lines in one direction and 1 line in the other direction

A

tuning fork artifact; center of rotation error; occurs in cardiac SPECT

101
Q

Causes of attenuation correction artifact

A

implanted hardware, IV contrast, oral barium, external jewelry, dense calcification

102
Q

Examples of scintillators (in nuclear medicine)

A

gamma camera, well counter, thyroid probe

103
Q

Decay type(s) with neutrino release

A

beta-minus, beta-positive decay

104
Q

Amount of energy required for beta-positive decay

A

1.022 MeV

105
Q

Mo-99 is produced by…

A

fission in a nuclear reactor

106
Q

FWHM of a photopeak is a measurement of…

A

system energy resolution

107
Q

Rubidium vs. F-18 positrons

A

rubidium positrons are higher energy => travel further prior to annihilation (gamma rays are still 511 keV)

108
Q

Linear energy transfer (LET)

A

amount of energy deposited in mass per unit length by the incident radiation; high LET particles deposit a large amount of radiation in a short distance (e.g. alpha particles)

AJT Physics (7 decks)

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