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COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS CH. 1 questions well answered
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COMPUTED TOMOGRAPHY FORTECHNOLOGISTS CH. 1
Spatial resolution - correct answer ✔✔Ability of a system to resolve as separate forms small objects that
are very close together. Also called high contrast resolution or detail resolution
Low contrast resolution - correct answer ✔✔the ability of the system to differentiate between objects
with similar densities
Temporal resolution - correct answer ✔✔Ability to deliver image detail in the smallest window of time.
z-axis - correct answer ✔✔Plane that correlates to the slice thickness or depth of the CT slice.
Collimators - correct answer ✔✔Mechanical hardware that resembles small shutters and adjusts the
opening based on the operators selection
Pixel - correct answer ✔✔Picture element. 2 dimensional square of data. When arranged in rows and
columns they make up the image matrix
Voxel - correct answer ✔✔Volume element. 3 dimensional cube of data acquired in CT
Matrix - correct answer ✔✔Grid formed by the rows and columns of pixels
Beam attenuation - correct answer ✔✔Phenomenon by which an X-ray beam passing through a
structure is decreased in intensity or amount because of absorption and interaction with matter. The
alteration in the beam varies with the density of the structure it passes through.
linear attenuation coefficient - correct answer ✔✔Amount of the X-ray beam that is scattered or
absorbed per unit thickness of the absorber is represented by the Greek letter mu.
, Positive contrast agents - correct answer ✔✔Contrast agents that are of a higher density than the
structure being imaged. Most contain barium or iodine.
Negative contrast agents - correct answer ✔✔A contrast agent that is of a lower density than the
surrounding structure, such as air or carbon dioxide.
Hounsfield Units (HU) - correct answer ✔✔Measure of the beam attenuation capability of a specific
structure. Also called pixel values, density numbers or CT numbers
polychromatic x-ray energy - correct answer ✔✔an x-ray beam that is composed of photons with varying
energies
Artifacts - correct answer ✔✔Objects seen on the image but not present in the object scanned.
beam-hardening artifacts - correct answer ✔✔artifacts that result from lower-energy photons being
preferentially absorbed, leaving higher-intensity photons to strike the detector array
Cupping artifacts - correct answer ✔✔Artifact that results from beam hardening. It appears on the image
as a vague area of increased density in a somewhat concentric shape around the periphery of an image,
similar to the shape of a cup.
volume averaging - correct answer ✔✔Process by which different tissue attenuation values are averaged
to produce one less accurate pixel reading. Also referred to as partial volume effect.
partial volume effect - correct answer ✔✔Process by which different tissue attenuation values are
averaged to produce one less accurate pixel reading. Also referred to as volume averaging.
raw data - correct answer ✔✔All measurements obtained from the detector array and sitting in the
computer waiting to be made into an image. Also called scan data
scan data - correct answer ✔✔All measurements obtained from the detector array and sitting in the
computer waiting to be made into an image. Also called raw data.
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