CT REGISTRY SAFETY QUESTIONS AND
ANSWERS WITH SOLUTIONS 2024
The quantity of radiation dose received by the patient from a series of CT scans is referred to as the: -
ANSWER The multiple-scan average dose (MSAD) is used to quantify the amount of exposure a patient
receives from a series of CT scans. It is calculated from the computed tomography dose index (CTDI)
through a series of equations. The quantity of radiation per scan is measured with an ionization
chamber.
Which of the following technical characteristics of a CT system does NOT directly affect patient dose? -
ANSWER Although they are beyond the control of the operator, the source-to-detector distance,
filtration, and detector efficiency of a CT system all directly affect patient dose. The selected FILAMENT
SIZE does have geometric ramifications with regard to spatial resolution. A smaller filament results in
improved spatial resolution. Patient dose is not affected by filament selection, provided that the mAs
value remains constant.
Which of the following statements most accurately describes the relationship between slice sensitivity
profile (SSP) and dose profile? - ANSWER The term slice sensitivity profile (SSP) may be used to describe
the reconstructed CT section. However, the section of tissue exposed to ionizing radiation, or dose
profile, is greater in width than the SSP.
The approximate radiation dose measured during a scan of a 100-mm-long pencil ionization chamber is
termed the: - ANSWER CTDI100 is a fixed measurement taken with a 100-mm-long pencil ionization
chamber inserted into an acrylic phantom. The CTDI100 standardizes the dose measurement from a
single axial scan and can be used to compare doses from different scan techniques.
The calculation of the average cumulative dose to each section within an acquisition of multiple sections
is termed the: - ANSWER The multiple-scan average dose (MSAD) is a calculation of the average
cumulative dose to each section within the center of a scan consisting of multiple sections. Because of
the contribution of scatter along the z-axis length of an acquisition, the MSAD for each section is higher
than the dose from an acquisition of a single section.
Automatic tube current modulation (ATCM) software is utilized by the CT system in an effort to: -
ANSWER Automatic tube current modulation (ATCM) is a form of automatic exposure control (AEC) for
CT systems. This type of software automatically DECREASES applied DOSE on the basis of the size,
density, and overall attenuation of the part being examined.
, The multiple-scan average dose (MSAD) is used to describe the: - ANSWER The multiple-scan average
dose (MSAD) is used to quantify the average cumulative dose to each section within the center of a scan
consisting of multiple sections.
Which of the following units is used to quantify absorbed dose? - ANSWER Absorbed dose describes the
amount of x-ray energy absorbed in a unit of mass. It is measured in gray (Gy).
Which of the following units is used to quantify effective dose? - ANSWER Effective dose approximates
the relative risk from exposure to ionizing radiation and is based on the radiosensitivity of a given tissue
type. It is measured in sievert (Sv).
The interaction between x-radiation and tissue that results in the complete loss of all x-ray photon
energy is called: - ANSWER Photoelectric absorption occurs when the energy of an incoming (incident) x-
ray photon is completely absorbed through the ionization of an inner-shell electron of the target atom.
Which of the following design characteristics of a CT system would result in an increased radiation dose
to the patient? 1. Decreased focus-to-isocenter distance 2. Decreased focus-to-detector distance 3.
Decreased filtration - ANSWER 1, 2, and 3
The acronym DLP is used to describe which of the following? - ANSWER Dose length product (DLP) is an
internationally accepted measure of CT patient dose defined as: DLP = MSAD × slice width (cm) × No. of
slices in scan volume.
A best practice for the use of in-plane bismuth shielding requires the: - ANSWER While in-plane bismuth
shielding is designed to be used within the acquisition range, it should be placed on the patient after the
localizer (scout) image(s) has/have been acquired.
Which of the following is the unit of radiation exposure? - ANSWER Exposure is the term used to
describe the ability of x-rays to ionize a volume of air. It is most commonly measured by the traditional
unit of roentgen (R). The International System of Units or SI unit for exposure is the coulomb per
kilogram (C/kg).
The interaction between x-radiation and tissue that results in a reduction in x-ray photon energy with a
subsequent change in photon direction is called: - ANSWER An incident x-ray photon may interact with a
target atom's outer-shell electron, transferring some energy that results in the ejection of the outer-shell
ANSWERS WITH SOLUTIONS 2024
The quantity of radiation dose received by the patient from a series of CT scans is referred to as the: -
ANSWER The multiple-scan average dose (MSAD) is used to quantify the amount of exposure a patient
receives from a series of CT scans. It is calculated from the computed tomography dose index (CTDI)
through a series of equations. The quantity of radiation per scan is measured with an ionization
chamber.
Which of the following technical characteristics of a CT system does NOT directly affect patient dose? -
ANSWER Although they are beyond the control of the operator, the source-to-detector distance,
filtration, and detector efficiency of a CT system all directly affect patient dose. The selected FILAMENT
SIZE does have geometric ramifications with regard to spatial resolution. A smaller filament results in
improved spatial resolution. Patient dose is not affected by filament selection, provided that the mAs
value remains constant.
Which of the following statements most accurately describes the relationship between slice sensitivity
profile (SSP) and dose profile? - ANSWER The term slice sensitivity profile (SSP) may be used to describe
the reconstructed CT section. However, the section of tissue exposed to ionizing radiation, or dose
profile, is greater in width than the SSP.
The approximate radiation dose measured during a scan of a 100-mm-long pencil ionization chamber is
termed the: - ANSWER CTDI100 is a fixed measurement taken with a 100-mm-long pencil ionization
chamber inserted into an acrylic phantom. The CTDI100 standardizes the dose measurement from a
single axial scan and can be used to compare doses from different scan techniques.
The calculation of the average cumulative dose to each section within an acquisition of multiple sections
is termed the: - ANSWER The multiple-scan average dose (MSAD) is a calculation of the average
cumulative dose to each section within the center of a scan consisting of multiple sections. Because of
the contribution of scatter along the z-axis length of an acquisition, the MSAD for each section is higher
than the dose from an acquisition of a single section.
Automatic tube current modulation (ATCM) software is utilized by the CT system in an effort to: -
ANSWER Automatic tube current modulation (ATCM) is a form of automatic exposure control (AEC) for
CT systems. This type of software automatically DECREASES applied DOSE on the basis of the size,
density, and overall attenuation of the part being examined.
, The multiple-scan average dose (MSAD) is used to describe the: - ANSWER The multiple-scan average
dose (MSAD) is used to quantify the average cumulative dose to each section within the center of a scan
consisting of multiple sections.
Which of the following units is used to quantify absorbed dose? - ANSWER Absorbed dose describes the
amount of x-ray energy absorbed in a unit of mass. It is measured in gray (Gy).
Which of the following units is used to quantify effective dose? - ANSWER Effective dose approximates
the relative risk from exposure to ionizing radiation and is based on the radiosensitivity of a given tissue
type. It is measured in sievert (Sv).
The interaction between x-radiation and tissue that results in the complete loss of all x-ray photon
energy is called: - ANSWER Photoelectric absorption occurs when the energy of an incoming (incident) x-
ray photon is completely absorbed through the ionization of an inner-shell electron of the target atom.
Which of the following design characteristics of a CT system would result in an increased radiation dose
to the patient? 1. Decreased focus-to-isocenter distance 2. Decreased focus-to-detector distance 3.
Decreased filtration - ANSWER 1, 2, and 3
The acronym DLP is used to describe which of the following? - ANSWER Dose length product (DLP) is an
internationally accepted measure of CT patient dose defined as: DLP = MSAD × slice width (cm) × No. of
slices in scan volume.
A best practice for the use of in-plane bismuth shielding requires the: - ANSWER While in-plane bismuth
shielding is designed to be used within the acquisition range, it should be placed on the patient after the
localizer (scout) image(s) has/have been acquired.
Which of the following is the unit of radiation exposure? - ANSWER Exposure is the term used to
describe the ability of x-rays to ionize a volume of air. It is most commonly measured by the traditional
unit of roentgen (R). The International System of Units or SI unit for exposure is the coulomb per
kilogram (C/kg).
The interaction between x-radiation and tissue that results in a reduction in x-ray photon energy with a
subsequent change in photon direction is called: - ANSWER An incident x-ray photon may interact with a
target atom's outer-shell electron, transferring some energy that results in the ejection of the outer-shell
