RadMath Boot Camp Flashcards
Measurement of exposure
Coulombs/kilogram
Unit of measurement for Air Kerma
Gy (Gy = 1 Joule/Kg)
Absorbed dose (D) Unit of measurement
Gy (D = 1 Joule/Kg)
Equivalent dose (EqD) unit of measurement
Sv
Equivalent dose (EqD) formula
EqD = D x Wr
Effective Dose (Dose) unit of measurement
Sv
Effective dose (Dose) formula
EfD = D x Wr X Wt
Exposure
measurement of ionizations in the air
Air Kerma
energy of ionizations in air
Equivalent Dose measures…
the biological damage of radiation in matter
Effective dose measures…
biological damage and is used to measure stochastic effects
Mass maintenance formula
mass-distance formula
mA1 D1^2
——— = ———-
mA2 D2^2
Inverse Square Law
I1 D2^2
—– = ———–
I2 D1^2
Image factors that affect image contrast
- kVp
- grids
- patient size
- scatter
- to a lesser extent, OID (e.g., air gap technique)
Image factors that affect spatial resolution
- SID
- OID
- Focal spot size
Image factors that affect distortion
- SID
- OID
- tube angle
- receptor angle
distortion
misrepresentation of size or shape of object being imaged
15% rule
if kVp goes up by 15%, mAs will decrease by half;
if kVp goes down by 15%, mAs will double
magnification
due to beam divergence, the image of an object is larger than the object itself
magnification factor equation
SID
MF = -------
SOD
OR
Image size
MF = ---------------------
Object sizeImage size equation related to magnification
Image size = Object size x MF
Object size equation related to magnification
Image
size
Object size = ————
MF
Factors that affect penumbra (focal spot blur)
- up = increase in blur
- Focal spot size
- OID
- up = decrease blur
- SOD
- SID
penumbra formula
OID
P = FSS x ——-
SOD
mm to in conversion
in = mm / 25.4
grid conversion chart
no grid 1
5: 1 2
6: 1 3
8: 1 4
10: 1 5 (or 4.5)
12: 1 5
16: 1 6
heat units formula
HU = kVp x mAs x MF
Modification factors for calculating HU
- single phase = 1
- 3-phase, 6P = 1.35
- 3-phase, 12P = 1.41
- HF = 1.45
