Dose Measurement

Question 1

What term is used to describe the reconstructed CT section?

Answer 1

slice sensitivity profile

Question 2

What term describes the section of tissue exposed to ionizing radiation and has a greater width than SSP?

Answer 2

dose profile

Question 3

What term is used to describe the ability of x-rays to ionize a volume of air?

Answer 3

exposure

Question 4

What is “exposure” measured in?

Answer 4

roentgens (R)

Question 5

What term describes the amount of x-ray energy absorbed in a unit of mass?

Answer 5

absorbed dose

Question 6

What is “absorbed dose” measured in?

Answer 6

grays (Gy)

Question 7

What is another term used to describe absorbed dose?

Answer 7

kerma

Question 8

What describes the amount of radiation absorbed in a quantity of air?

Answer 8

air kerma

Question 9

What accounts for the type of tissue radiation is deposited in?

Answer 9

effective dose (EfD)

Question 10

What factor determines the weighting factors that are assigned to different tissues?

Answer 10

individual radiosensitivity

Question 11

What is effective dose used to calculate from exposure to ionizing radiation?

Answer 11

risk

Question 12

What is effective dose measured in?

Answer 12

sieverts (Sv)

Question 13

What is also the estimation of the whole-body dose equivalent that results from the partial body exposure the patient receives during a CT procedure?

Answer 13

effective dose

Question 14

What is an approximate measurement of the dose received in a sinlge CT section or slice?

Answer 14

CT dose index (CTDI)

Question 15

What is calculated from the central slice of a series when 7 slices surround each side?

Answer 15

CTDI

Question 16

What measurement is taken with a 100-mm-long pencil ionization chamber and makes no reference to a specific number of slices?

Answer 16

CTDI-100

Question 17

What causes dose to vary within the image across the acquired FOV?

Answer 17

absorption

Question 18

What measurement is calculated by the sum of 2/3 of periphery and 1/3 of central exposure of the field?

Answer 18

CTDI-w

Question 19

What dosimeter measures and calculates radiation exposure for CTDI-w?

Answer 19

TLD’s

Question 20

What is measured using the axial or “step-and-shoot” method of scanning?

Answer 20

CTDI-w

Question 21

What is used to measure radiation dose from the helical scan method?

Answer 21

CTDI-vol

Question 22

What is the formula for calculating CTDI-vol?

Answer 22

CTDI-vol = CDTI-w/pitch

Question 23

As pitch increases, what happens to the dose per section?

Answer 23

decreases

Question 24

What axis planes does the CTDI-w approximate dose and what is it measured in?

Answer 24

x- and y- axis; mGy

Question 25

What axis planes does the CTDI-vol approximate dose and what is it measured in?

Answer 25

z-axis; mGy

Question 26

What is CTDI-vol similar to?

Answer 26

MSAD- multiple scan average dose

Question 27

What is a calculation of the average cumulative dose to each slice within the center of a scan consisting of multiple slices?

Answer 27

MSAD

Question 28

What does MSAD take in account for which makes the average dose higher in a single slice?

Answer 28

scatter radiation

Question 29

Are the MSAD doses from the beginning and end slices more or less than the central slice?

Answer 29

less

Question 30

What is the formula for calculate MSAD?

Answer 30

MSAD = T/I x CTDI

Question 31

What does MSAD account for when calculating dose from an axial scan?

Answer 31

image spacing or "bed index"

Question 32

Do overlapping scans in axial scanning increase or decrease dose?

Answer 32

increase

Question 33

Does having gaps between slices in axial scanning increase or decrease dose?

Answer 33

decrease

Question 34

When slice thickness is greater than image spacing, does MSAD increase or decrease?

Answer 34

increase

Question 35

When slice thickness is less than image spacing, does MSAD increase or decrease?

Answer 35

decrease

Question 36

What is MSAD controlled by during a helical scan?

Answer 36

pitch

Question 37

What is the formula for calculating MSAD of a helical scan?

Answer 37

MSAD= CTDI/pitch

Question 38

What is the MSAD dose when slice thickness is equal to image spacing?

Answer 38

equal

Question 39

What term describes the amount of table travel per tube rotation divided by the collimation?

Answer 39

pitch

Question 40

What part of a scan series is MSAD most accurate?

Answer 40

center

Question 41

What two measurements are used to calculate the average radiation dose within a scan volume?

Answer 41

CTDI-vol and MSAD

Question 42

dose amongst what scan plane is not considered in the average radiation dose calculated by CTDI-vol and MSAD?

Answer 42

z-axis

Question 43

What is the formula for DLP?

Answer 43

DLP= CTDI-vol x scan length (collimation) x No. of slices in scan volume

Question 44

What is the formula for DLP when using CTDI-vol and scan length to calculate the total dose and what is it measured in?

Answer 44

DLP= CTDI-vol x scan length; mGy-cm

Question 45

What setting controls the CTDI-vol?

Answer 45

prepatient collimator

Question 46

What object is used to determine the measurement of effective dose since calculating a direct measurement is not possible?

Answer 46

phantom

Question 47

What factor is not accounted for by CTDI-vol and DLP and typically leads to under- or over-estimation of dose?

Answer 47

patient size

Question 48

What two other ways may CTDI-vol and DLP be expressed as?

Answer 48

computed tomography air kerma index (Ca) and air kerma length product (Pkl)

Question 49

What report is included by DICOM to give information regarding tube's radiation output during CT acquisition like: tube current and voltage, scan time, acquisition length, pitch, and collimation width?

Answer 49

RDSR- Radiation Dose Structured Report

Question 50

Does the RDSR report automatically get archived into the patient's electronic medical record?

Answer 50

yes

Question 51

What is a new automated alert system that indicates when the anticipated dose for a given acquisition exceeds the recommended maximum?

Answer 51

dose check

Question 52

What are the two levels of check associated with dose check systems?

Answer 52

dose notification and dose alert

Question 53

Which dose check system informs the technologist when the prescribed technical settings for an individual CT acquisition may result in a CTDI-vol or DLP higher than a preset recommended value?

Answer 53

dose notification

Question 54

Which dose check system alerts the technologist when the prescribed acquisitions for an entire CT exam results in a CTDI-vol and DLP higher than preset value?

Answer 54

dose alert

Question 55

What four requirements have CT systems been designed to obtain to reduce patient exposure?

Answer 55

automated CT dose check separate protocols for adults and pediatrics DICOM structured reporting AEC