Computed Tomography Terminology
Algorithm - correct answer ✔✔Set of mathematical calculations and processes applied in image
reconstruction.
Artifact - correct answer ✔✔Undesirable feature or density in an image not representative of the
anatomy.
CT (computed tomography) - correct answer ✔✔Radiographic examination that displays sectional
anatomic images in axial, sagittal, or coronal planes.
CT number - correct answer ✔✔Number that represents the attenuation value for each voxel, relative to
water. Also called Hounsfield units (after Hounsfield who helped to invent the first CT machine). Your
term section in the reading says value for each pixel, but actually it is for each voxel. You see these voxel
values (one side them) in a pixel/2D format on the monitor.
Gantry - correct answer ✔✔Component of a CT system that houses the x-ray tube, detectors, and
collimators.
Isotrophic - correct answer ✔✔Having the same value of a property in all directions. An example in
regular x-ray is that the x-ray beam created in the regular x-ray tube is emitted off the anode in all
directions (it is just that some of the photons get absorbed into the anode, some shoot up in the tube
and the lead housing absorbs it, some go down to through the tube window to the patient, etc. So a
regular x-ray beam is said to be isotrophically emitted. In CT- the term- "isotrophic" is used to describe
that in each voxel the representative data set is uniform throughout. In other words, even though a piece
of anatomy could potentially be smaller than one voxel (therefore this would mean various intensities in
that voxel), each voxel is created with through "volume averaging," meaning the CT number value
(Hounsfield unit) for that voxel is averages and given a uniform value throughout that voxel.
(This is why, folks, a picture is just a picture. It is not reality. It is as close as we can get with technology,
but we can't truly see anatomy until you actually see it. This is why, no matter the modality, that some
pathologies can be missed, or never seen at all.)
Linear attenuation coefficient. - correct answer ✔✔Numeric expression of the decrease in radiation
intensity that follows transmission through matter.
Algorithm - correct answer ✔✔Set of mathematical calculations and processes applied in image
reconstruction.
Artifact - correct answer ✔✔Undesirable feature or density in an image not representative of the
anatomy.
CT (computed tomography) - correct answer ✔✔Radiographic examination that displays sectional
anatomic images in axial, sagittal, or coronal planes.
CT number - correct answer ✔✔Number that represents the attenuation value for each voxel, relative to
water. Also called Hounsfield units (after Hounsfield who helped to invent the first CT machine). Your
term section in the reading says value for each pixel, but actually it is for each voxel. You see these voxel
values (one side them) in a pixel/2D format on the monitor.
Gantry - correct answer ✔✔Component of a CT system that houses the x-ray tube, detectors, and
collimators.
Isotrophic - correct answer ✔✔Having the same value of a property in all directions. An example in
regular x-ray is that the x-ray beam created in the regular x-ray tube is emitted off the anode in all
directions (it is just that some of the photons get absorbed into the anode, some shoot up in the tube
and the lead housing absorbs it, some go down to through the tube window to the patient, etc. So a
regular x-ray beam is said to be isotrophically emitted. In CT- the term- "isotrophic" is used to describe
that in each voxel the representative data set is uniform throughout. In other words, even though a piece
of anatomy could potentially be smaller than one voxel (therefore this would mean various intensities in
that voxel), each voxel is created with through "volume averaging," meaning the CT number value
(Hounsfield unit) for that voxel is averages and given a uniform value throughout that voxel.
(This is why, folks, a picture is just a picture. It is not reality. It is as close as we can get with technology,
but we can't truly see anatomy until you actually see it. This is why, no matter the modality, that some
pathologies can be missed, or never seen at all.)
Linear attenuation coefficient. - correct answer ✔✔Numeric expression of the decrease in radiation
intensity that follows transmission through matter.
