COMPUTED TOMOGRAPHY (CT) -
SPECIALTY EXAM QUESTIONS AND
ANSWERS
Air calibration - Answer-Scan of air in gantry; based on a known value of -1000 for air,
the scanner calibrates itself according to this density value relative to actual density
value measured.
algorithm - Answer-Mathematic formula designed for computers to carry out complex
calculations required for image reconstruction; designed for enhancement of soft tissue,
bone, and edge resolution. also referred to as kernel
anisotropic spatial resolution - Answer-spatial resolution of a voxel in which all three
axes of the volume element are not equal. slice thickness is not equal to pixel size.
aperture - Answer-opening of the gantry through which patient passes during scan
archiving - Answer-storage of CT images on long term storage device such as cassette
tape, magnetic tape, or optical disk.
artifact - Answer-distortion or error in image that is unrelated to subject being studied
attenuation - Answer-coefficient CT number assigned to measured remnant radiation
intensity after attenuation by tissue density.
axial - Answer-describes plane of image as presented by CT scan; same as transverse.
bolus - Answer-preset amount of radiopaque contrast medium injected rapidly per IV
administration to visualize high flow vascular structures, usually in conjunction with
dynamic scan; most often injected using a pressure injector.
channel - Answer-in multidectector CT, multiple rows of detectors (channels) are
arranged along the longitudinal (z) axis of the patient. each detector row(channel)
consists of numerous elements.
Computed Tomography (CT) - Answer-xray tube and detector assembly rotating 360
degrees around a specified area of the body; also called CAT (Computed Axial
Tomography)
Computed tomography dose index (CTDI) - Answer-Radiation dose descriptor
calculated with normalized beam widths for 14 contiguous sections or slices
, Computed tomography dose index 100 (CTID100) - Answer-radiation dose descriptor
calculated with the full length of a 100 mm pencil ionization chamber. Measures larger
scan distances than CTDI, but only one location is calculated.
Computed tomography dose indexvol (CTDIvol) - Answer-Radiation dose descriptor that
takes into account the parameters that are related to a specific imaging protocol.
considers helical pitch or axial scan spacing in its calculation. more accurate measure of
dose per protocol.
Computed tomography dose indexw (CTDIw) - Answer-radiation dose descriptor that
provides a weighted average of the center and peripheral contributions to dose within
the scan plane. more accurate than CTDI100 owing to calculations from more than one
location.
CT angiography - Answer-use of volumetric CT scanning with spiral technique to
acquire image data that are reconstructed into three dimensional CT angiograms.
CT number - Answer-Arbitrary number assigned by computer to indicate relative density
of a given tissue; CT number varies proportionately with tissue density; high CT
numbers indicate dense tissue, and low CT numbers indicate less dense tissue. all CT
numbers are based on the density of water, which is assigned a CT number of 0. also
referred to as a Hounsfield unit.
contrast resolution - Answer-ability to differentiate between small variations in density
within the image.
curved planar reformations - Answer-post processing technique applied to stacks of
axial image data that can be reconstructed into irregular or oblique planes
data acquisition system (DAS) - Answer-Part of detector assembly that converts analog
signals to digital signals that can be used by the CT computer.
Detector - Answer-electronic component used for radiation detection; made of either
high density photo reactive crystals or pressurized stable gases.
detector assembly - Answer-Electronic component of CT scanner that measures
remnant radiation exiting the patient, converting the radiation to an analog signal
proportionate to the radiation intensity measured.
direct coronal - Answer-Describes position used to obtain images in coronal plane; used
for head scans to provide images at right angles to axial images; patient is positioned
prone for direct coronal images and supine for reverse coronal images
Dose length product (DLP) - Answer-commonly reported dose descriptor on cT
scanners. Calculated by multiplying the CTDLvol by the length of the scan (cm).
SPECIALTY EXAM QUESTIONS AND
ANSWERS
Air calibration - Answer-Scan of air in gantry; based on a known value of -1000 for air,
the scanner calibrates itself according to this density value relative to actual density
value measured.
algorithm - Answer-Mathematic formula designed for computers to carry out complex
calculations required for image reconstruction; designed for enhancement of soft tissue,
bone, and edge resolution. also referred to as kernel
anisotropic spatial resolution - Answer-spatial resolution of a voxel in which all three
axes of the volume element are not equal. slice thickness is not equal to pixel size.
aperture - Answer-opening of the gantry through which patient passes during scan
archiving - Answer-storage of CT images on long term storage device such as cassette
tape, magnetic tape, or optical disk.
artifact - Answer-distortion or error in image that is unrelated to subject being studied
attenuation - Answer-coefficient CT number assigned to measured remnant radiation
intensity after attenuation by tissue density.
axial - Answer-describes plane of image as presented by CT scan; same as transverse.
bolus - Answer-preset amount of radiopaque contrast medium injected rapidly per IV
administration to visualize high flow vascular structures, usually in conjunction with
dynamic scan; most often injected using a pressure injector.
channel - Answer-in multidectector CT, multiple rows of detectors (channels) are
arranged along the longitudinal (z) axis of the patient. each detector row(channel)
consists of numerous elements.
Computed Tomography (CT) - Answer-xray tube and detector assembly rotating 360
degrees around a specified area of the body; also called CAT (Computed Axial
Tomography)
Computed tomography dose index (CTDI) - Answer-Radiation dose descriptor
calculated with normalized beam widths for 14 contiguous sections or slices
, Computed tomography dose index 100 (CTID100) - Answer-radiation dose descriptor
calculated with the full length of a 100 mm pencil ionization chamber. Measures larger
scan distances than CTDI, but only one location is calculated.
Computed tomography dose indexvol (CTDIvol) - Answer-Radiation dose descriptor that
takes into account the parameters that are related to a specific imaging protocol.
considers helical pitch or axial scan spacing in its calculation. more accurate measure of
dose per protocol.
Computed tomography dose indexw (CTDIw) - Answer-radiation dose descriptor that
provides a weighted average of the center and peripheral contributions to dose within
the scan plane. more accurate than CTDI100 owing to calculations from more than one
location.
CT angiography - Answer-use of volumetric CT scanning with spiral technique to
acquire image data that are reconstructed into three dimensional CT angiograms.
CT number - Answer-Arbitrary number assigned by computer to indicate relative density
of a given tissue; CT number varies proportionately with tissue density; high CT
numbers indicate dense tissue, and low CT numbers indicate less dense tissue. all CT
numbers are based on the density of water, which is assigned a CT number of 0. also
referred to as a Hounsfield unit.
contrast resolution - Answer-ability to differentiate between small variations in density
within the image.
curved planar reformations - Answer-post processing technique applied to stacks of
axial image data that can be reconstructed into irregular or oblique planes
data acquisition system (DAS) - Answer-Part of detector assembly that converts analog
signals to digital signals that can be used by the CT computer.
Detector - Answer-electronic component used for radiation detection; made of either
high density photo reactive crystals or pressurized stable gases.
detector assembly - Answer-Electronic component of CT scanner that measures
remnant radiation exiting the patient, converting the radiation to an analog signal
proportionate to the radiation intensity measured.
direct coronal - Answer-Describes position used to obtain images in coronal plane; used
for head scans to provide images at right angles to axial images; patient is positioned
prone for direct coronal images and supine for reverse coronal images
Dose length product (DLP) - Answer-commonly reported dose descriptor on cT
scanners. Calculated by multiplying the CTDLvol by the length of the scan (cm).
