Radiation Safety And Dosimetry

Question 1

Amount of filtration within the CT X-ray tube

Answer 1

Between 6 and 9 mm aluminum (Al) or equivalent material

Question 2

Ability of the detector to capture transmitted X-ray quanta and produce the appropriate response

Answer 2

Inherent absorption efficiency

Question 3

Spatial arrangement of detector elements, including the amount of interspace material required between adjacent elements

Answer 3

Geometric efficiency

Question 4

Multi-slice CT utilizes a ______ instead of a fan-shaped beam (single-slice)

Answer 4

Cone-shaped

Question 5

Expansion of the primary beam in a MSCT system to ensure that all detectors of the array are exposed to X-rays of equal intensity

Answer 5

Overbeaming

Question 6

Occurs when radiation dose is applied before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms inherent in spiral (helical) CT

Answer 6

Overranging

Question 7

Employed during the reconstruction process to reduce displayed noise within the CT image

Answer 7

Noise reduction algorithms or adaptive filters

Question 8

• decrease in the focal spot-detector distance
• use of a cone beam instead of a more z-axis collimated fan beam
• increases in the number of phases of acquisition enabled by decreased scan times
• use of thinner section widths for improvement of 3D and MPR images

Answer 8

Dose in MSCT is considerably higher

Question 9

Process of adjusting parameters such as mA/kVp, Alice thickness, and pitch to reduce patient dose

Answer 9

Protocol optimization

Question 10

Section of tissue (patient) exposed to radiation

Answer 10

Dose profile

Question 11

Increase in collimation (thinner slices) yield images with more noise. Increase mA to compensate for image noise and does what to patient dose

Answer 11

Increases

Question 12

Wider collimation ~ improved dose efficiency because less overbeaming occurs

Answer 12

Narrow beam widths (thin slices) ~ increase overbeaming and reduce dose efficiency

Question 13

Mathematical filter applied to raw data during CT image reconstruction to remove the blurring artifact inherent to back-projection

Answer 13

Kernel (algorithm)

Question 14

Ability of X-rays to ionize a volume of air. Measured in roentgens (R)

Answer 14

Exposure

Question 15

Amount of X-ray energy absorbed in a unit of mass. Measured in grays (Gy)

Answer 15

Absorbed dose

Question 16

Amount of radiation absorbed in a quantity of air. Also used to describe absorbed dose

Answer 16

Air kerma/kerma

Question 17

Accounts for the type of tissue that radiation is deposited in. Measured in sieverts (Sv)

Answer 17

Effective dose

Question 18

Approximate measure of the dose received in a single CT section or slice

Answer 18

CT dose index (CTDI)

Question 19

Weighted dose index ~ uses measurements from center and periphery. Dose along the x and y axes (mGy)

Answer 19

CTDI w

Question 20

Used to approximate the radiation dose for each section obtained during a helical scan. Dose along the z axis (mGy)

Answer 20

CTDI vol

CTDI vol = CTDI w/
Pitch

Question 21

Amount of table travel per tube rotation divided by the collimation.
Or, relationship between collimation and table movement per gantry rotation

Answer 21

Pitch

Question 22

Measurement of dose for an entire series of CT images. Is equal to the calculated dose per section multiplied by the length of a CT acquisition along the z-axis

Answer 22

Dose length product (DLP)

DLP = CTDI vol x scan length