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36 Cards in this Set
- Front
- Back
Equation for quantiative transmission (ie how many photons penetrate through a certain substance)
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N = No x e^-ut
No= # of original photons u- linear attenuation coefficient t= thickness |
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Grid Ratio
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grid ratio = H/W
H=height of lead W= width of gap |
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Bucky Factor
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BF = dose to patient with grid/dose to patient without grid
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Minification gain
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input area/output area
i.e. (di/do)^2 di=input diameter do=output diameter |
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Brightness gain
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flux gain x minification gain
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CTDIvol
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CTDIvol=CTDIw/Pitch
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Dose length product (DLP)
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DLP = CTDIvol x scan length
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# of nuclei at time t (Nt)
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Nt = No e^-h-t
No= # of original nuclei h=decay constant t=time |
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Decay constant (h)
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h = 0.69/T1/2
*long T1/2 = short h |
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Activity
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Activity = h Nt
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Cummulative Activity
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A = 1.44 x f x initial activity x effective half life
A= cummulative activity f = 1 for whole body (different weights for different organs) |
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Effective half life
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1/Te = 1/Tp + 1/Tb
Te= effective half life Tp= physical half life Tb = biological half life |
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Dose to a a particular organ
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D = S x A
S= S factor (from a book) A =Activity |
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Hounsfield Units
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HU = 1000 (ux - uwater)/uwater
ux = annenuation of material uwater = attenuation of water |
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Pitch
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Pitch = D/W
D= distance per revolution W= beam width |
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Wave equation
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velocity = frequency x wavelength
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Acoustic impedance
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Acoustic impedance (Z) = p x v
p = density v= velocity |
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Wavelength based on transducer thickenss
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wavelength = 2 x trasnducer thickness
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Pulse length
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pulse length = 2 * wavelength
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Near field in US
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near field = r^2 x wavelength
r = radius of transducer |
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Axial resolution in US
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Axial resolution = SPL/2
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fractional SD
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SD = 1/sqrt N
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Power
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power = voltage x current
measured in watts (joule/s) |
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Energy
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energy = power x time
measured in joules |
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Best achievable digital resolution
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best achievable digital resolution = 0.5 x (1/pixel size)
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Sensitiivty
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Sensitivity = TP/(TP + FN)
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Specificity
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Specificity = TN/(TN + FP)
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Accuracy
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Accuracy = (TP + TN)/(TP + FP + TN + FN)
i.e. true positives and true negatives /over everything |
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Prevalence
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Prevalence = (TP + FN)/(TP + FP + FN + TN)
i.e. true positives + things that are actually true but were construed as false/over everything |
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Positive predictive value
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PPV = TP/(TP + FP)
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Negative predictive value
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NPV = TN/(TN + FN)
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Mass attenuation
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u/p
u = linear attenuation coefficient p= density thus mass attenuation is independent of density! |
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HVL
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HVL = 0.693/u
u = linear attenuation coefficient |
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Photon energy
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E = h f = h (c/wavelength)
f= Planck's constant c= speed of light f= frequency |
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Inverse square law
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(x1/x2)^2
x1 = distance 1 x2 = distance 2 |
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optical density
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OD = log (Io/It)
Io = light incident on film It = light transmitted |