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CT Patient Care III
Radiation Dosimetry in CT
| Question | Answer |
|---|---|
| Equals 1 rad. There are 100 rad in 1 gray (Gy) | centigray (cGy) |
| An equipment option that will make changes in mA based on estimated attenuation of the patient at specific location. Estimations come from AP & lat scouts or previous slices. From these views, mA will be programmed to vary by location along length of pt | automatic tube current modulation |
| Dose reported to the FDA; slices must be contiguous | computed tomography dose index (CTDI) |
| Result when the CTDI is measured using a pencil ionization chamber. This 100-mm-long thin cylindrical device is long enough to span the width of 14 contiguous 7-mm slices. Provides better estimate of MSAD for thin slices than single-slice method | CTDI 100 |
| Adjusts for variation across the scan field of view by providing a weighted average of measurements at the center and the peripheral slice locations (i.e., x and y dimensions of the slice) | CTDIw |
| Measure of exposure per slice and is independent of scan length. It is the preferred expression of radiation dose in CT dosimetry | CTDIvol |
| CTDIvol X scan length. Although this more closely reflects the radiation dose for a specific CT exam, its value is affected by variances in patient anatomy | dose-length product (DLP) |
| A measurement, reported in Sv or rem, that attempts to acct for effects particular to the pt's tissues that has absorbed the dose. Extrapolates risk of partial body exp to pts from data obtained from whole body doses to bomb survivors. | effective dose |
| A system that is used internationally, body in everyday commerce and in science | International System of Units (SI) |
| SI unit of absorbed dose | gray (Gy) |
| Total dose is the central slice radiation dose, plus the scatter overlap (or tails); dose calculated from multiple scans | multiple scan average dose (MSAD) |
| When x-ray penumbra falls outside the active detectors; this occurs when collimators are opened so that the same x-ray intensity reaches all of the detectors in an MDCT system | overbeaming |
| The estimated radiation dose to radiosensitive organs from CT procedures. These averages are used to calculate effective dose | organ dose |
| A conversion factor that's applied to absorbed dose that accts for different biologic effects produced from different types of ionizing rad'n; 1 for diag x-rays that are used in CT. When this has been applied to rad, new quantity is called dose equivalent | quality factor (Q) |
| Unit of x-ray exposure in air | roentgen (R) |
| Unit of absorbed dose | radiation absorbed dose (rad) |
| Whenthe quality factor has been applied to the radiation absorbed dose, the new quantity is called the dose equivalent. The unit for dose equivalent is the ____ | roentgen equivalents man (rem) |
| Variations along the length, or z axis, of the patient; also referred to as the z-axis dose distribution | radiation profile |
| Once the quality factor has been applied to the radiation absorbed dose the new quantity is called the dose equivalent. The SI equivalent is the ___. There are 100 rem in 1 __ | sievert (Sv) |
| Areas of scatter radiation into the tissue of adjacent slices | tails |
Created by:
sspatel
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