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CT registry Prep

Dose Measurements

TermDefinition
Dose Profile area of tissue exp to radiation per slice.
Exposure ability of xrays to Ionize a volume of air. measured in Roentgens (R)
Absorbed Dose amt of xray energy absorbed in a unit of mass. measured in Grays (Gy)
Kerma describes amnt of radiation in a unit of air.
Effective Dose (efd) accounts for different types of tissue and their assigned weighted factors. Weighted factors are determined by radiosensitivity. approximates amt of relative risk measured in Sieverts (sv)
Ct Dose index CTDI approx. measure of dose received in a single section/slice. Calculated for he central slice in a series
CTDI100 fixed measurement taken with a 100mm long pencil ionization chamber.
CTDIw internationally accepted weighted dose index. calculated by adding 2/3 of the exposure at the periphery of the field plus 1/3 of the centrally located dose. More accurate than dose approximation. Only for Step and Shoot Axial measured in milligray (
CTDIvol approx. dose for each section during a helical scan. CTDIvol=CTDIw/pitch as pitch increases, dose per slice decreases and CTDIvol decreases. measured in milligray (mGy)
MSAD Multiple scan average dose older term for CTDIvol. Avg cumulative dose to each slice in the center of the scan with multiple slices. MSAD=slice thickeness/increments(spacing)
MSAD for Axial when slice thickness is equal to bed index(pitch), msad is equal to the CTDI
MSAD for Helical/Spiral MSAD=CTDI/Pitch where pitch=amnt of table travel per tube rotation divided by collimation.
Dose Length Product (DLP) measure of CT dose. DLP=MSAD x slice thickness x number of slices in scan volume. or DLP=CTDIvol x scan length
Created by: ashton.harward