Term
In a female patient, gonadal shielding may be applied during which of the following CT examinations?
1. Chest
2. Abdomen
3. Brain
A. 3 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3 |
|
Definition
D. 1, 2, and 3
Gonadal shielding may be used whenever the gonads do not lie within the area of clinical interest. Gonadal shielding in the female patient is most difficult during CT scanning of the pelvis. |
|
|
Term
The quantity of radiation dose received by the patient from a series of CT scans is referred to as the:
A. MSAD.
B. XCAL.
C. CTDI.
D. MTF. |
|
Definition
A. MSAD
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. |
|
|
Term
Which of the following technical characteristics of a CT system does NOT directly affect patient dose?
A. Source-to-detector distance
B. Filtration
C. Detector efficiency
D. Filament size |
|
Definition
D. Filament size
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. |
|
|
Term
Radiation protection of the CT patient should involve which of the following principles?
1. Strict clinical indication
2. Protocol optimization
3. Shielding
A. 1 only
B. 3 only
C. 2 and 3 only
D. 1, 2, and 3 |
|
Definition
D. 1, 2, and 3
Specific clinical indications ensure that CT is performed only when alternative non-ionizing radiation examinations have been deemed inconclusive or inappropriate. An optimized protocol is one that acquires CT images with acceptable levels of noise at the lowest possible dose. Lead shielding should be utilized during CT whenever clinically possible. |
|
|
Term
Which of the following statements most accurately describes the relationship between slice sensitivity profile (SSP) and dose profile?
A. The SSP is always wider than the dose profile.
B. The SSP is equal in width to the dose profile.
C. The dose profile is always wider than the SSP.
D. The SSP has no effect on the dose profile. |
|
Definition
C. The dose profile is always wider than the SSP.
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. |
|
|
Term
The approximate radiation dose measured during a scan of a 100-mm-long pencil ionization chamber is termed the:
A. MSAD.
B. effective dose.
C. CTDIvol.
D. CTDI100. |
|
Definition
D. CTDI100.
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. |
|
|
Term
The calculation of the average cumulative dose to each section within an acquisition of multiple sections is termed the:
A. CTDIw.
B. CTDI100.
C. kerma.
D. MSAD. |
|
Definition
D. MSAD
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. |
|
|
Term
When the mAs value utilized for a given CT acquisition is doubled, which of the following occurs?
A. Image noise increases.
B. Spatial resolution decreases.
C. Patient dose increases.
D. Contrast resolution decreases. |
|
Definition
C. Patient dose increases.
There is a direct and proportional relationship between mAs and patient dose. When the mAs value for a given exposure is doubled, patient dose is also doubled. |
|
|
Term
Automatic tube current modulation (ATCM) software is utilized by the CT system in an effort to:
A. improve temporal resolution.
B. decrease patient dose.
C. save on energy costs.
D. improve spatial resolution. |
|
Definition
B. decrease patient dose.
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. |
|
|
Term
The multiple-scan average dose (MSAD) is used to describe the:
A. dose received in a single CT section.
B. amount of radiation absorbed in a quantity of air.
C. average dose to a single section within a scan of multiple sections.
D. cumulative dose for an entire helical scan. |
|
Definition
C. average dose to a single section within a scan of multiple sections.
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. |
|
|
Term
Which of the following units is used to quantify absorbed dose?
A. Roentgens (R)
B. Gray (Gy)
C. Sievert (Sv)
D. Curie (Ci) |
|
Definition
B. Gray (Gy)
Absorbed dose describes the amount of x-ray energy absorbed in a unit of mass. It is measured in gray (Gy). |
|
|
Term
Which of the following units is used to quantify effective dose?
A. Roentgen (R)
B. Gray (Gy)
C. Sievert (Sv)
D. Curie (Ci) |
|
Definition
C. Sievert (Sv)
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). |
|
|
Term
Which of the following technical adjustments would result in a decrease in patient dose?
1. Decrease mAs.
2. Increase detector pitch.
3. Decrease kVp.
A. 2 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2, and 3 |
|
Definition
D. 1, 2, and 3
The relationship between mAs and dose is directly proportional. Any reduction in mAs results in a reduction in dose when all other factors remain equal. Increasing detector pitch raises the rate at which the patient moves through the gantry during data acquisition; when all other factors remain constant, increases in detector pitch reduce patient dose. A decrease in kVp also results in lower patient dose primarily through the reduction in overall beam energy at lower tube potentials. This may seem counterintuitive to those who recall the use of high-kVp techniques in radiography as a means of lowering required mAs and the associated patient dose. When we reduce kVp to reduce patient dose in CT, the assumption is again made that all other technical factors remained unchanged. |
|
|
Term
The interaction between x-radiation and tissue that results in the complete loss of all x-ray photon energy is called:
A. Compton scatter.
B. attenuation.
C. photoelectric absorption.
D. photodisintegration. |
|
Definition
C. photoelectric absorption.
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. |
|
|
Term
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
A. 3 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3 |
|
Definition
D. 1, 2, and 3
A reduction in the distance between the x-ray tube (focus) and the gantry isocenter or the tube and detectors would result in an increased patient dose according to the inverse square law. The purpose of filtration is to remove the unwanted, "low-quality" portion of the x-ray beam that adds to the patient radiation dose while failing to yield useful acquisition data. A reduction in system filtration would result in an increase in patient exposure to low-quality radiation. |
|
|
Term
The acronym DLP is used to describe which of the following?
A. A specialized CT imaging technique used to measure bone mineral density
B. A quality control test that measures the accuracy of the laser lighting system
C. A high-speed CT scanner used for cardiac imaging
D. The radiation dose to the patient during a CT scan |
|
Definition
D. The radiation dose to the patient during a CT scan
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. |
|
|
Term
Which of the following technical factors has a direct effect on patient dose?
A. Kernel
B. kVp
C. Window width
D. Display field of view (DFOV) |
|
Definition
B. kVp
A decrease in kVp with no compensatory change in other technical factors (mA, scan time, pitch, etc.) will result in a significant decrease in the quantity of x-radiation produced by the CT tube and a subsequent decrease in patient exposure and dose. |
|
|
Term
Which of the following technical changes would serve to decrease patient radiation dose during a CT examination?
A. Increased matrix size
B. Increased display field of view (DFOV)
C. Increased level of tolerated image noise
D. Increased kVp |
|
Definition
C. Increased level of tolerated image noise
If more noise is tolerated in the reconstructed CT image, technical factors including mAs and kVp may be reduced, resulting in decreased patient dose. |
|
|
Term
Which of the following methods may be employed to reduce the radiation dose to the pediatric patient undergoing CT?
1. Decreased kVp
2. Decreased mAs
3. Decreased pitch
A. 2 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3 |
|
Definition
B. 1 and 2 only
The "child-sizing" of CT protocols is an important method of reducing radiation dose to the pediatric patient. A reduction in both kVp and mAs will result in decreased tube output and reduced patient dose. A decreased pitch would slow patient movement through the gantry, subsequently increasing patient dose. |
|
|
Term
A best practice for the use of in-plane bismuth shielding requires the:
A. shield to be placed above and below the patient.
B. placement of shield before the acquisition of scout (localizer) images.
C. shield to remain outside of the scan acquisition range.
D. placement of shield after the acquisition of scout (localizer) images. |
|
Definition
D. placement of shield after the acquisition of scout (localizer) images.
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. This is important for proper functioning of the automatic tube current modulation (ATCM) systems employed by modern CT scanners. |
|
|
Term
Which of the following pitch settings would result in the lowest radiation dose to the patient?
A. 1.0
B. 1.2
C. 1.7
D. 2.0 |
|
Definition
D. 2.0
All other factors remaining consistent, the higher the pitch, the greater the dose savings at a cost of x-axis resolution. |
|
|
Term
As part of a comprehensive approach to minimize CT radiation exposure to the pediatric patient, the technologist should:
1. Apply out-of-plane lead (or equivalent) shielding to protect radiosensitive tissues.
2. Reduce the technical parameters (e.g., mA, kVp) based upon the patient size/weight.
3. Eliminate unnecessary contrast enhancement phase acquisitions.
A. 2 only.
B. 1 and 3 only.
C. 2 and 3 only.
D. 1, 2, and 3. |
|
Definition
D. 1, 2, and 3.
"Child-sizing" technical parameters, using appropriate shielding, and eliminating unnecessary enhancement phase acquisitions are all valuable components of a comprehensive dose reduction approach for pediatric patients. |
|
|
Term
Which of the following is the unit of radiation exposure?
A. Roentgen (R)
B. Sievert (Sv)
C. Becquerel (Bq)
D. Gray (Gy) |
|
Definition
A. Roentgen (R)
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). |
|
|
Term
Assuming no other changes are made, which of the following would reduce patient exposure during CT?
A. Decrease the pitch from 1.5 to 1.0.
B. Increase kVp from 100 to 140.
C. Increase the tolerated noise level of the acquired images.
D. Increase the scan field of view (SFOV) from small to large. |
|
Definition
C. Increase the tolerated noise level of the acquired images.
Tolerating a noisier image allows for decreased technical parameters (mAs, kVp) resulting in a significant patient dose savings. Technologists are encouraged to work with their interpreting practitioners (i.e., radiologists) to determine an image noise level that balances the diagnosticity of the examination with an effort to minimize patient dose. |
|
|
Term
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:
A. photoelectric absorption.
B. Compton scatter.
C. photodisintegration.
D. Bremsstrahlung. |
|
Definition
B. Compton scatter
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 electron (ionization). This results in a loss of energy for the incident x-ray photon and a subsequent change in direction. This physical interaction between x-ray and matter is called Compton scattering. |
|
|
Term
Assuming no other technical adjustments are made, an increase in the applied tube potential (kVp) used for a CT acquisition will result in a:
A. decreased dose length product (DLP).
B. increased dose length product (DLP).
C. decreased CTDIvol.
D. more than one, but not all of the above. |
|
Definition
B. increased dose length product (DLP).
There is a direct and exponential relationship between the kilovoltage-peak (kVp) setting and patient radiation dose. An increase in kVp with no compensatory change in other technical factors (mA, scan time, pitch, etc.) will result in a significant increase in the quantity of x-radiation produced by the CT tube and a subsequent increase in patient exposure and dose, as quantified by the dose length product (DLP). |
|
|
Term
When employing in-plane bismuth shielding, a thin spacer material may be positioned to reduce:
A. streaking artifact.
B. spatial resolution.
C. magnification.
D. patient discomfort. |
|
Definition
A. streaking artifact.
A disadvantage of bismuth shielding is the streaking artifact that may occur on the image. A thin foam spacer may be placed between the patient surface and the bismuth shielding material to reduce the scatter artifact. |
|
|
Term
A dose check system features which of the following?
1. Dose notification
2. Dose alert
3. Dose report
A. 3 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3 |
|
Definition
B. 1 and 2 only
Modern CT systems may also employ an automated alert system called dose check that indicates when the anticipated dose for a given acquisition exceeds the recommended maximum. A dose check system typically consists of both a dose notification for individual acquisitions and a dose alert warning for entire CT studies. |
|
|
Term
Current CT systems employ which of the following image reconstruction methods to reduce patient radiation dose?
A. Interpolation
B. Filtered back-projection
C. Iterative reconstruction
D. Convoluted reconstruction |
|
Definition
C. Iterative reconstruction
Iterative reconstruction techniques may be used by a CT system to reduce patient dose. As compared with the standard filtered back-projection method of CT image reconstruction, iterative reconstruction can reduce image noise associated with the low-dose techniques employed to reduce patient exposure. |
|
|
Term
Current industry standards require that data related to the tube output during CT acquisition be documented in the RDSR which stands for:
A. Required Dose System Report.
B. Radiation Diagnostic Signal Response.
C. Regulatory Dose Status Report.
D. Radiation Dose Structured Report. |
|
Definition
D. Radiation Dose Structured Report.
The Radiation Dose Structured Report (RDSR) serves as a standardized method of archiving the patient exposure information for each CT acquisition. It typically includes tube current and voltage, scan time, acquisition length, pitch, and collimation width. |
|
|
Term
Assuming no other technical adjustments are made, when the kVp utilized for a given CT acquisition is increased, which of the following occurs?
A. Signal-to-noise ratio
B. Spatial resolution increases
C. Increased patient dose
D. Decreased patient dose |
|
Definition
C. Increased patient dose
There is a direct and exponential relationship between the kilovoltage-peak (kVp) setting and patient radiation dose. An increase in kVp with no compensatory change in other technical factors (mA, scan time, pitch, etc.) will result in a significant increase in the quantity of x-radiation produced by the CT tube and a subsequent increase in patient exposure and dose. |
|
|
Term
During CT data acquisition, the section of the patient exposed to radiation may be referred to as the:
1. Slice
2. Dose profile
3. Pitch
A. 1 only.
B. 1 and 2 only.
C. 1 and 3 only.
D. 1, 2, and 3. |
|
Definition
B. 1 and 2 only
During CT data acquisition, the section of the patient exposed to radiation may be referred to as the dose profile. This may also be referred to as the acquired slice, or the slice sensitivity profile (SSP). |
|
|
Term
Which of the following statements regarding CT image noise is TRUE?
A. As the mAs for a given CT acquisition increases, image noise decreases.
B. As the selected DFOV for a CT image decreases, noise decreases.
C. As patient size decreases, noise increases.
D. As patient size decreases, noise decreases. |
|
Definition
D. As patient size decreases, noise decreases
Image noise is directly related to patient size. As a patient size decreases, noise decreases. Based on this relationship, CT protocols should include size-based dose (mAs) adjustments. |
|
|
Term
Which of the following describes the system that adjusts the mA setting according to part size variations along the z-axis?
A. Longitudinal tube current modulation
B. Temporal tube current modulation
C. Angular tube current modulation
D. Automated tube voltage selection |
|
Definition
A. Longitudinal tube current modulation
Longitudinal (z-axis) tube current modulation adjusts the mA setting as the scan proceeds along the z-axis of the patient. |
|
|
Term
Which of the following descriptors accounts for the dose effects of image spacing during axial acquisition?
A. CTDIvol
B. CTDIw
C. EfD
D. MSAD |
|
Definition
D. MSAD
MSAD accounts for the effects of image spacing, or bed index, on the patient dose during axial scanning. During axial scanning, overlapping scans increase the patient radiation dose, whereas gaps between slices decrease it. |
|
|
Term
The reduction in overall intensity of the CT x-ray beam as it interacts with the scanned patient is termed:
A. absorption.
B. attenuation.
C. photodisintegration.
D. scatter. |
|
Definition
B. Attenuation
Attenuation is defined as the reduction of intensity of a radiation beam as it passes through a substance. |
|
|
Term
Attenuation of the CT x-ray beam occurs through which of the following physical interactions?
1. Compton scatter
2. Photoelectric absorption
3. Pair production
A. 2 only
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only |
|
Definition
B. 1 and 2 only
Attenuation of the CT x-ray beam consists of two physical properties. Photoelectric absorption describes the complete absorption of the incident x-ray energy as photons ionize target atoms. Incident photons that undergo the Compton scatter interaction lose some portion of their x-ray energy and undergo a subsequent change in direction. |
|
|
Term
Because of the bow-tie filter employed in the CT x-ray system, positioning the patient at isocenter is critical to avoid:
A. streaking artifact.
B. quantum mottle.
C. reduced contrast resolution.
D. increased patient exposure. |
|
Definition
D. increased patient exposure.
Positioning the patient in the center of the gantry (isocenter) is critical when a bow-tie filter is employed. Positioning the patient off-center relative to the gantry and the bow-tie filter can result in unwanted variations in patient exposure and dose. |
|
|
Term
An optimized protocol is one that acquires CT images:
A. in the shortest time possible, regardless of the patient dose.
B. of the highest quality, regardless of the patient dose.
C. with acceptable noise levels at the lowest possible patient dose.
D. during all possible phases of contrast enhancement, regardless of the patient dose. |
|
Definition
C. with acceptable noise levels at the lowest possible patient dose.
An optimized protocol is one that acquires CT images with acceptable levels of noise at the lowest possible dose, while still delivering images of diagnostic quality. |
|
|
Term
The CT dose index (CTDI) is calculated for the central slice in a series that is surrounded by ______ slices on each side.
A. three
B. four
C. five
D. seven |
|
Definition
D. seven
The CT dose index (CTDI) is an approximate measure of the dose received in a single CT section or slice. It is calculated for the central slice in a series that is surrounded by seven slices on each side. |
|
|
Term
When the slice thickness for a given CT acquisition equals the image spacing, the:
A. MSAD is equal to the CTDI.
B. MSAD is less than the CTDI.
C. MSAD is greater than the CTDI.
D. MSAD and CTDI remain unrelated. |
|
Definition
A. MSAD is equal to the CTDI.
MSAD increases when slice thickness is greater than image spacing—overlapping scans. MSAD decreases when slice thickness is less than the bed index—noncontiguous scans. When slice thickness equals the bed index, MSAD is equal to CTDI. |
|
|
Term
The dose length product of a CT acquisition may be calculated as the product of the CTDIvol and the:
A. milliamperage (mA).
B. kilovoltage (kV).
C. bed index (image spacing).
D. scan length. |
|
Definition
D. scan length.
The DLP may be illustrated as the product of CTDIvol and scan length and is given in units of milligray-centimeters (mGy-cm). |
|
|
Term
Which of the following technical factor adjustments would result in a decrease in the CTDIvol for a given acquisition?
A. Increased milliamperage (mA)
B. Increased display field-of-view (DFOV)
C. Increased pitch
D. Increased kilovoltage (kV) |
|
Definition
C. Increased pitch
CTDIvol is used to approximate the radiation dose for each section obtained during a helical scan. It corresponds to the axially acquired CTDIw divided by the helical pitch. As the pitch increases, the dose per section (CTDIvol) decreases |
|
|
Term
A CT system may employ a focal spot tracking system to precisely direct the x-ray beam toward the detector array in an effort to reduce:
A. signal-to-noise ratio.
B. contrast resolution.
C. overbeaming.
D. star artifact. |
|
Definition
C. overbeaming
Some CT manufacturers employ focal spot tracking systems to finely control the position of the x-ray beam on the detectors, reducing overbeaming and subsequent radiation exposure. |
|
|
Term
In the interaction known as Compton scattering, an incident x-ray photon loses energy undergoes a change in direction after interacting with a target atom’s:
A. inner-shell electron.
B. outer-shell electron.
C. nucleus.
D. protons. |
|
Definition
B. outer-shell electron
A Compton scatter interaction occurs when an incident x-ray photons interacts with a target atom’s outer-shell electron. The transfer of energy ejects the outer-shell electron (ionization), resulting in a loss of energy for the incident x-ray photon and a subsequent change in photon direction (scatter). |
|
|
Term
Attenuation of the CT x-ray beam is dependent upon:
1. Photon energy of the x-ray beam
2. Atomic density of the tissue
3. Geometric efficiency of the detector array
A. 1 only.
B. 2 only.
C. 1 and 2 only.
D. 1, 2, and 3. |
|
Definition
C. 1 and 2 only
Attenuation of the CT x-ray beam depends on the beam quality (photon energy) and the atomic density of the imaged tissue. Only after passing through the patient is the transmitted radiation incident upon an array of CT detectors. |
|
|
Term
The CT x-ray beam is filtered in order to:
A. reduce overall patient dose.
B. improve spatial resolution.
C. reduce image magnification.
D. remove convolution artifact. |
|
Definition
A. reduce overall patient dose.
Filtration acts to remove the unwanted, "low-quality" portion of the x-ray beam that adds to the patient radiation dose while failing to yield useful acquisition data. |
|
|
Term
Iterative reconstruction of CT data reduces patient exposure by limiting image:
A. sensitivity profile.
B. acquisition time.
C. noise.
D. resolution. |
|
Definition
C. noise
Iterative reconstruction techniques may be used by a CT system to reduce patient dose. As compared with the standard filtered back-projection method of CT image reconstruction, iterative reconstruction can reduce image noise associated with the low-dose techniques employed to reduce patient exposure. |
|
|
Term
The x-ray beam used in a multidetector CT system may be best described as a:
A. pencil beam.
B. fan beam.
C. cone beam.
D. linear beam. |
|
Definition
C. cone beam
To expose the widened detector array equally, MDCT utilizes a cone-shaped beam instead of the fan-shaped beam traditionally used by single-slice CT (SSCT) systems. |
|
|
Term
The radiation dose to the patient will increase if:
1. Image noise is decreased
2. Pitch is decreased
3. Focus-to-detector distance is decreased
4. Filtration is decreased
5. Scan length is decreased
A. 4 only.
B. 2, 3, and 4.
C. 1, 2, 3, and 4.
D. all (1 to 5) are correct. |
|
Definition
C. 1, 2, 3, and 4
Image noise is reduced by increased radiation dose. A decreases in pitch would reduce the speed at which the patient is moved through the gantry, thus increasing dose. Decreased filtration would allow "low-quality" x-ray photons to reach the patient, increasing dose. A structural decrease in the focus-to-detector distance by the CT manufacturer would result in an increase in patient dose, based upon the inverse square law. |
|
|
Term
______________ describes the overall ability of CT detectors to measure transmitted x-ray photons as it relates to their spatial arrangement within the gantry.
A. Geometric efficiency
B. Inherent efficiency
C. Quantum efficiency
D. Kerma efficiency |
|
Definition
A. Geometric efficiency
The geometric efficiency of a detector array describes the spatial arrangement of detector elements, including the amount of interspace material required between adjacent elements. |
|
|
Term
During helical CT acquisition, there is a small amount of x-ray exposure just before and immediately following the anatomical volume of interest. This may be referred to as:
A. photon flux.
B. overbeaming.
C. overranging.
D. photon fluence. |
|
Definition
C. overranging
Overranging occurs when radiation dose is applied before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms inherent in spiral CT. |
|
|
Term
Radiation protection in CT should follow the ALARA concept, which stands for:
A. as limited as the radiologic allows.
B. as little as regionally acceptable.
C. as long as readily available.
D. as low as reasonably achievable. |
|
Definition
D. as low as reasonably achievable.
Radiation protection in CT should follow the ALARA (as low as reasonably achievable) concept. |
|
|
Term
When employing ECG-triggered tube current modulation during a cardiac CT, as the patient heart rate increases, the radiation dose savings:
A. decrease.
B. increase.
C. remain the same.
D. vary randomly. |
|
Definition
A. decrease
The potential radiation dose savings gained with ECG-triggered tube current modulation depend on the patient’s heart rate. As heart rate increases, the radiation dose savings decrease. A faster heart rate results in less time between successive points in the cardiac cycle, resulting in fewer opportunities for a reduction in tube current. |
|
|
