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215 Cards in this Set
- Front
- Back
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Electron energy
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511 KeV
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Energy of visible light
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1-3 eV
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Ionizing energy
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~30 eV
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Velocity (equation, waves)
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V = f x λ
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Potential power of 3 phase power supply
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~100 KW
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Max power of single phase power supply (110V 60 Hz)
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~3 KW
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Definition of Amp
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1 C / s
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Power (equation, electricity)
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P = V x I (volts X current)
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Watt (definition)
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J / s
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Joule (definition)
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W x s
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Average ripple of 3-phase (12 pulse) power supply
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~4%
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Penetration distance of electrons in W target
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~1mm
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Tungsten K-edge
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70 KeV
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Iodine K-edge
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33 KeV
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Average photon energy (in standard x-ray tube)
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1/3 - 1/2 max energy
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% characteristic x-rays produced from x-ray tube
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Always < 10%
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Relationship of x-ray production and mAs
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x-rays α mAs (linear)
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Relationship of x-ray production and kV
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x-rays α kV squared
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Tube filament current and amperage
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~4 A x 10 V (40 W)
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Size of focal spots in general radiology
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1.2 mm, 0.6 mm
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Magnitude of tube currents in fluoroscopy
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~1-5 mA
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Average chest x-ray settings (Kv/Ma/s)
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140 kV; 500 mA; 5 mS
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Fluoro tube power loading
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~100-500 W
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Maximum power loading for standard focal spots (100 mS exposure)
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1.2 mm - 100kW
0.6 mm - 25 kW |
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Coherent scatter (e.g. Rayleigh or classical scatter)
% of interactions |
Photon is absorbed into atom and a scatter photon with the same frequency is produced
~ <5% of interactions in diagnostic radiology |
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Photoelectric effect relationship to atomic number
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Photoelectric Effect α 1/Z^3
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Photoelectric effect relationship to photon energy
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Photoelectric Effect α 1/E^3
(e.g.) 40 keV -> 80 keV; 1/8 PE effect |
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Compton Scatter relationship to electron density
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CS α electron density
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Compton scatter relationship to photon energy
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CS α 1/E
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Photoelectric and Compton interactions are equal at:
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25 keV
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Attenuation equation
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N = N0 x e^-μt
N0 - starting # of photons μ - linear attenuation coeff (cm-1) t - absorber thickness (cm) |
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Mass attenuation coefficient
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MAC = μ / ρ
μ - linear attenuation coeff ρ - density |
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Heel effect
Relationship to anode angle Side of increased intensity |
Heel effect increases as anode angles get smaller
Stronger on cathode (+) side |
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Grid ratio (formula)
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Grid ratio = H / W
H - Height of grid elements W - Space between grid elements |
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Bucky Factor (formula)
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BF = incident/transmitted radiation
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Bucky factor for KUB
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~5-10
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Grids not used for
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Extremity radiography
CT |
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Air Kerma (definition, units)
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Kinetic energy released per unit mass
Gy (J/Kg) |
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Entrance air Kerma
Chest Skull Abdomen |
Chest ~0.1 mGy
Skull ~1.5 mGy Abd ~3 mGy |
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Energy required to blacken screen-film
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5 μGy
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Half Value Layer (HVL)
Relationship to E avg Relationship to filtration Required HVL at 80 kVp |
increased kV -> increased HVL
Increased filtration -> increased HVL 2.5 mm Al |
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Film exposure to achieve density of 1.5
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5 μGy
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Steepest part of the Characteristic curve is called
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The Gamma region
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Film latitude (definition)
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Range of air kerma over which the film density is satisfactory
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Film density (equation)
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D = Log incident light/transmitted light
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Representative penetration values for given film densities
OD 1 OD 2 OD 3 |
OD 1 = 10%
OD 2 = 1% OD 3 = 0.1% |
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Barium K-edge
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37 keV
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Gadolinium K-edge
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50 keV
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Screens and relation to patient dose and exposure time
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Screens reduce patient dose and exposure time
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Intensification factor of screens
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30-50 times
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Screen thickness in screen-film systems
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200 μM
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Gas detectors use which gas
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Xenon
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Scintillator
Material Conversion efficiency Advantages/disadvantages |
CsI
~10% Very sensitive, High Z Light spreads out causing less sharp images |
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Photostimulable phosphor matieral (most common)
Used in |
BaFBr
CR |
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Photoconductors
Material K-edge Advantages Disadvantages |
Selenium
10 keV Sharp images Low Z, poor efficiency at Diag doses |
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Ratio of digital to analog latitude
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10,000:1
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Worker protection:
Total effective dose equivalent |
5 rem/yr (50 mSv)
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Worker protection:
ICRP/NCRP effective dose limits |
20mSv/yr averaged over 5 years
No more than 50 mSv/yr |
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Worker protection:
ICRP/NCRP lifetime dose |
10 mSv x age
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Worker protection:
Public dose limit |
1 mSv/yr
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Worker protection:
Fetal limit (month/total) |
0.5 mSv/mo & 5 mSv total
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Worker protection:
Eye dose limit |
150 mSv/yr
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Worker protection:
Extremity dose limit |
500 mSv/yr
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Alpha decay
Particle composition Energy/spectra Example compound Dominant above |
2 protons, 2 neutrons (He nucleus)
4-7 MeV/discrete energy levels 226Ra --> 222Rn Dominant decay Z>82 |
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Isobars
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Atomic mass units unchanged
Examples B-, B+, EC decay |
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Isomers
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A,Z,N unchanged
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Isotones
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N unchanged
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Isotopes
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Z unchanged
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β- decay
Examples |
A same, Z+1, N-1
Emits β- and antineutrino 32P, 3H, 14C |
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β+ decay
Examples |
A same, Z-1, N+1
Emits β+ and neutrino 18F, 11C, 15O |
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Electron capture
Examples |
A same, Z-1, N+1
Emits gamma and neutrino 67Ga, 111In, 123I, 201Tl |
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Isomeric transition
Metastable time Example |
A,Z,N unchanged
Metastable if t1/2 > 10^-9 s 99m-Tc |
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β- decay energy
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Spectrum of energies with average at 1/3 Emax
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Positron average energy
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~0.25 MeV
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Positron range in soft tissue
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~0.6 mm
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Likely decay from elements created in nuclear reactor
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β-
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Likely decay from elements created in cyclotron
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β+, EC
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Curie (definition)
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3.7 x 10^10 nuclear transformations/sec
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Bequerel (definition)
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1 nuclear transformation/sec
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Nuclear decay (equation)
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Nt = No x e^-λt
Nt - nuclei at time = t No - original # nucleai λ - decay constant |
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Decay constant (equation)
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λ = 0.69 / T1/2
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Activity (equation)
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Activity = λ x Nt
λ - decay constant Nt - Nuclei at time t |
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Secular equilibrium
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Equilibrium obtained when parent has long T1/2
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Transient equilibrium
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Equilibrium obtained when parent has short T1/2
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Radiation dose to organ (equation)
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D = S x A
S=factor Cumulative activity (# trans) |
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Cumulative activity (equation)
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Cumulative activity = 1.44 x initial activity x Effective t1/2
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Effective half-life (equation)
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1/Te=1/Tp + 1/Tb
Tp = physical t1/2 Tb = biological t1/2 must be less than physical and biological t1/2 |
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Secular equilibrium
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Equilibrium obtained when parent has long T1/2
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Transient equilibrium
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Equilibrium obtained when parent has short T1/2
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Radiation dose to organ (equation)
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D = S x A
S=factor Cumulative activity (# trans) |
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Cumulative activity (equation)
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Cumulative activity = 1.44 x initial activity x Effective t1/2
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Effective half-life (equation)
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1/Te=1/Tp + 1/Tb
Tp = physical t1/2 Tb = biological t1/2 must be less than physical and biological t1/2 |
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Effective half life of I-131 in thyroid (number)
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~4 days
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Maximum organ doses in nuc med studies (number)
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~50 mGy
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99m-Tc
energy decay |
140 keV
isomeric transition |
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123-I
energy decay |
160 keV
electron capture |
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18-F
energy decay |
511 keV
β+ |
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67-Ga
energy decay |
184 keV
Electron capture |
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111-In
energy decay |
247 keV
Electron capture |
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131-I
energy decay |
364 keV
Electron capture |
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Fraction of gamma rays that get through a typical NM collimator
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0.0001 (1 in 10,000)
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Pinhole collimator image
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Magnified and inverted
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Scintillator material in NM
Light output |
NaI
10% |
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Relation of photon energy and % photons detected (NM)
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Decreases
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Parallel hole collimators
Image size Relation of FOV with distance |
Same size image
FOV doesn't change with distance |
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High sensitivity collimators
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Large holes and low resolution
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High resolution collimators
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Smaller holes and higher resolution
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Thickness of NaI crystal of gamma camera
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~10mm
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Full-width Half Maximum (NM)
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Photopeak width
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Energy resolution (NM)
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Breadth of photopeak
Ex: 123-I (160 keV) with measured FWHM of 16 keV = 10% energy resolution |
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Number of counts for average NM image
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~500K
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SPECT
Number of projections per rotation |
~100
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SPECT
matrix size |
128 x 128
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SPECT
Reconstruction Advantages |
Iterative reconstruction
More accurate, reduces artifacts |
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18-F resolution
Soft tissue Lung |
1mm
Worse in lung due to lower density |
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PET
Detector substance Dimensions |
LSO, GSO
~3mm x 3mm x 3cm |
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PET
reconstruction |
Iterative reconstruction
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Attenuation correction inaccurate with
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Metals, lung lesions.
Estimating attenuation at CT energy (~120 keV) for 511 keV annihilation photons |
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NM
Matrix Image size |
128 x 128
1/64 MB (1 Byte/pixel) |
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Gamma camera resolution
Intrinsic Collimator |
3 mm
8 mm |
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NM
System resolution (equation) |
R = (R intrinsic^2 + R coll^2)^-0.5
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NM reference source
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137-Cs
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RADIOBIOLOGY
Indirect damage Direct damage (Mechanism and fractions) |
Indirect: photons create radicals (2/3)
Direct: Energetic electrons (1/3) |
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RADIOBIOLOGY
Sensitive phase(s) of cell cycle |
M > G1 phases
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RADIOBIOLOGY
Resistant phase(s) of cell cycle |
S phase
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RADIOBIOLOGY
Radiosensitive tissues |
Red marrow, colon, breast, stomach, lung
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RADIOBIOLOGY
Least sensitive cells |
Nerve
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RADIOBIOLOGY
High LET |
Alpha particles
Double-stranded breaks along single axis --> less likely repaired; more cell death |
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RADIOBIOLOGY
Low LET DNA effects # lesions Location |
Same # lesions as high LET but usually SS breaks in separate locations which can be more easily repaired
Higher doses of low LET needed to cause same damage |
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RADIOBIOLOGY
Hematopoietic syndrome dose range time to effect |
2-5 Gy
Death in 3 weeks |
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RADIOBIOLOGY
GI syndrome dose range time to effect |
10 Gy
Death in 5-10 days |
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RADIOBIOLOGY
Cerebrovascular syndrome Dose range Time to effect |
100 Gy
Death in 1-2 days |
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RADIOBIOLOGY
Deterministic effects (definition) |
Harmful tissue reactions
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RADIOBIOLOGY
Stochastic effects (definition) |
Probabilistic effects - no threshold dose.
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RADIOBIOLOGY
Skin Transient erythema Time to onset |
2 Gy
Hours |
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RADIOBIOLOGY
Skin Non-transient erythema Time to onset |
6 Gy
1-2 weeks |
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RADIOBIOLOGY
Skin Temporary epilation Time to onset |
3 Gy
2-3 weeks |
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RADIOBIOLOGY
Skin Permanent epilation Time to onset |
>7 Gy
2-3 weeks |
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RADIOBIOLOGY
Cataracts Acute dose Chronic dose |
~ 2 Gy
~ 5 Gy |
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RADIOBIOLOGY
Sterility Male doses: Temporary, Permanent (single, mult) |
0.5 Gy, 3 Gy (chronic), 6 Gy (single dose)
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Sterility
Female doses: Permanent in premenopausal |
~ 2 Gy
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UNITS
Roentgen relationship to air kerma (mGy) 60 kVp |
1 R = 8.7 mGy
1 mGy = 0.114 R |
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UNITS
Gy and Rad |
1 Gy = 100 rad
1 rad = 10 mGy |
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UNITS
Sv and rem |
1 Sv = 100 rem
1 rem = 10 mSv |
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UNITS
Ci and Bq |
1 Ci = 3.7 X 10^10 Bq
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US
Pulsed doppler SPL Axial resolution |
Longer SPL = 5-25 cycles/pulse
Axial resolution worse |
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US
Thermal Index |
Ratio of the acoustic power produced by the transducer to the power required to raise the temp 1 degree C.
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US
Mechanical Index Definition Relationship to power, freq change |
Mechanical Index
Cavitation potential from the rarefaction of the waves. Increases linearly with the power Inversely proportional to the square root of the freq change |
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IMAGE QUALITY
Most important determinant of contrast |
KeV
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IMAGE QUALITY
Collimation relation to scatter |
Collimation reduces scatter
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IMAGE QUALITY
3 items that effect blur |
Focal spot
Motion Receptor |
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IMAGE QUALITY
Blur vs magnification |
increased magnification increases blur
(no mag = no focal spot blur) |
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IMAGE QUALITY
Blur vs ss/ds film |
Single-sided film has less blur
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IMAGE QUALITY
Basic unit of resolution in Fluoro DR CT |
Fluoro = TV line width
DR = pixel size CT = Detector element size |
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IMAGE QUALITY
Line spread function Relation to screen speed |
How much radiation "spreads out"
Wider with faster screens |
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IMAGE QUALITY
MTF Total (formula) |
MTF total = MTF focus x MTF screen x MTF motion
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IMAGE QUALITY
Resolution (LP) Film alone Film + thick screen Mammo |
>20 LP / mm
5 LP / mm 12 LP / mm |
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IMAGE QUALITY
TV resolution Kell |
250 LP
70% or 180 is functional resolution |
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IMAGE QUALITY
TV bandwith (500 line TV) |
5 MHz
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IMAGE QUALITY
Spatial resolution fluoroscopy II TV |
II = 5 LP/mm
TV 1 LP/mm (500 line TV) |
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IMAGE QUALITY
Fluoro collimators Effect on dose, resolution |
Collimators don't affect resolution or dose
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IMAGE QUALITY
Nyquist frequency Definition Equation |
Best achievable digital resolution
0.5 x sampling frequency |
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IMAGE QUALITY
Resolution: Digital chest x-ray Digital photospot Digital mammo CT |
Digital chest 3 LP/mm
Photospot - 2 LP/mm Mammo - 7 LP/mm CT - 0.7 LP/mm |
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Poisson distribution relationshop to Gaussian
As N increase: Standard deviation Relative variation |
Poisson = Gaussian n>10
Standard deviation increases Relative variation decreases |
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IMAGE QUALITY
CT noise level in dB |
+/- 3 dB
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IMAGE QUALITY
Factors increasing mammo contrast |
Low photon E
Compression High gamma film Gris |
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IMAGE QUALITY
Factors increasing mammo resolution |
Thin screen
Small focal spot Compression |
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IMAGE QUALITY
Factors increasing mammo mottle |
higher currents (200 uGy)
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IMAGE QUALITY
Sensitivity |
TP / TP + FN
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IMAGE QUALITY
Specificity |
TN / TN + FP
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IMAGE QUALITY
Positive predictive value |
TP / TP + FP
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IMAGE QUALITY
Negative predictive value |
TN / TN + FN
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IMAGE QUALITY
ROC X and Y axes |
X - (1-specificity)
Y - sensitivity |
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ACCURACY (FORMULA)
|
TP + TN / TP + TN + FP + FN
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Accuracy and relation to disease incidence
|
When low incidence, accuracy can be high, even if all studies called (-) --> Sensitivity = 0 and specificity = 100%
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RADIOBIOLOGY
Prodromal syndrome Dose Symptoms |
0.5 - 1 Gy (50 - 100 rads)
Anorexia, nausea, vomiting |
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RADIOBIOLOGY
Effective dose is used to estimate what types of effects |
Stochastic (cancer and heritable defects)
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RADIOBIOLOGY
Risk of fatal cancer per Sv Risk of severe heredity effects |
4%
0.6% |
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MAMMOGRAPHY
MQSA Average glandular dose per image |
3 mGy
|
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X-RAY PRODUCTION
Mechanisms of production and % |
Bremsstrahlung 90%
Characteristic 10% |
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X-RAY PRODUCTION
Efficiency (% energy converted to x-rays) |
1%
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CT
Dose to breast from CT exam |
10 mGy
|
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MAMMOGRAPHY
Compression relation to average glandular dose |
Lower AGD
|
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MRI
Gauss Tesla relationship |
1 Tesla = 10,000 Gauss
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MRI
Number of parallel / antiparallel and relationship to magnetic field strength |
Excess of 3-4 spins / million (parallel vs. anti-parallel) at 1 Tesla. This increases with increasing magnetic field.
10^15 extra spins per average voxel |
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MRI
Larmor frequency |
42.58 MHz / Tesla
Proportional to field strength |
|
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MRI
Diamagnetic |
Oppose the magnetic field
Ex: Ca, H2O, organic materials |
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|
MRI
Paramagnetic |
Slightly positive susceptibility to externally applied magnetic field. Enhance local magnetic field.
No measurable self-magnetization Ex: oxygen, gadolinium, blood breakdown products |
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|
MRI
Ferromagnetic |
"Superparamagnetic"
Self-magnetization. Augment external field considerably. Ex: iron, cobalt, nickel |
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Larmor equation
|
ωo = γ x Bo
ωo - Precessional angular frequency γ - gyromagnetic ratio Bo - Magnetic field strength |
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Free Induction Decay
Induced by Frequency Decays with |
Induced by transverse magnetization vector .
Oscillates at Larmor freq Decays with loss of phase coherence |
|
|
Time for FID to reach half original intensity
|
T = 0.693 x T2
|
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Spin - Spin
|
T2
Loss of phase coherence due to intrinsic magnetic properties of the sample. |
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MRI
Spin - Lattice |
T1
Exponential regrowth of Mz Depends on spin characteristics of the molecular lattice |
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MRI
Relative length of T1, T2, T2* |
T1 > T2 > T2*
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MRI
Relationship of field strength and T1, T2 |
T1 is lengthened with higher B0
T2 is unchanged |
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MRI
FID decays proportional to |
T2* decay constant
|
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MRI
TE |
Point of rephasing of transverse magnetization after 180 degree pulse
|
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MRI
TR |
Time between successive 90 degree pulses
Short TR can have saturation - incomplete relaxation Short T1 tissue has less saturation than long T1 tissue |
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MRI
T1 |
Short TR
Short TE ~400-600, 5-30 |
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MRI
PD |
Long TR
Short TE ~1500-3500, 5-30 |
|
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MRI
T2 |
Long TR
Long TE ~1500-3500, 60-150 |
|
|
MRI
Inversion recovery |
180 - 90 - 180 - 180
TI is chosen to null out various tissues |
|
|
MRI
STIR |
Short tau inversion recovery
Fat suppression and reduction of chemical shift artifacts ~180 ms |
|
|
MRI
FLAIR |
Fluid-attenuated Inversion Recovery
Nulls out water-bound anatomy and CSF ~2400 ms Long TR 7000 ms |
|
|
Gray units related to Joules
|
1 J / Kg
|
|
|
MRI
Chemical shift artifact fixes |
Decrease magnetic field strength
Increase bandwidth Increase gradient Use fat saturation |
|
|
MRI
Chemical shift artifact Due to differences in: Which direction |
Resonance frequencies of fat and water
Frequency encoding |
|
|
CT
CTDIw CTDIvol DLP |
CTDIw = 2/3 CTDI periph + 1/3 CTDI center
CTDIvol = CTDIw / pitch DLP = CTDIvol x scan length |
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CT
DLP is proportional to |
Total dose imparted to patient
|
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CT
HU equation |
HU = 1000 (μ tissue - μ water/μ water)
|
|
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CT
HU depends on |
Filtration and KVp
|
|
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Radiation Protection
Intensity of scattered radiation at 1M |
0.1%
|
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FLUORO
Brightness Gain |
BG = Minification gain x flux
|
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FLUORO
Minification gain |
MG = (D input / D output)^2
|
