COMPUTED TOMOGRAPHY FOR
TECHNOLOGISTS EXAM 2025/2026
QUESTIONS AND ANSWERS 100% PASS
What is spatial resolution? - ANS the ability of a system to define small objects distinctly
what is low-contrast resolution? - ANS the ability of a system to differentiate on the image
objects with similar densities
what is temporal resolution? - ANS the speed that the data can be acquired (high speed can
help eliminate motion artifacts)
what is the "z" axis? - ANS the thickness of the slice (plane)
what is the "x" axis? - ANS width
what is the "y" axis? - ANS height
what does the term "voxel" stand for? - ANS volume element
what is the most common matrix size? - ANS 512 x 512 (262,144)
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,what is attenuation? - ANS the degree to which the x-ray beam is reduced by an object
what determines the shades of gray on the image? - ANS the quantities of x-ray photons that
pass through the object and actually strike the detector
define density - ANS the mass of a substance per unit volume
the higher the density, the more opportunities for photon interaction
what is linear attenuation coefficient? (μ) - ANS the amount of x-ray beam that is scattered or
absorbed per unit thickness of the absorber
what is the linear attenuation coefficient for water? - ANS 0.18cm⁻¹
basically this means that 18% of x-ray beams are absorbed or scattered when they pass through
1 centimeter of water
the attenuation coefficient ___________ with increasing photon energy, and ___________ with
increasing atomic number & density - ANS decreases, increases
differences in linear attenuation coefficients are responsible for what? - ANS they are
responsible for x-ray image contrast
the values in CT images are sometimes referred to as ________ - ANS density
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,1 HU equals a ______% difference between the linear attenuation coefficient of the tissue as
compared with the linear attenuation coefficient of water - ANS 0.1%
beam-hardening artifacts - ANS artifacts that result from the preferential absorption of the
low-energy x-ray photons (leaving only the high intensity beams behind)
what type of artifact causes dark streaks and vague areas of decreased density? - ANS beam-
hardening artifacts
beam-hardening artifacts are aka? - ANS cupping artifacts
thicker CT slices increases the likelihood of what? - ANS missing very small objects
what is volume averaging? - ANS the process in CT by which different tissue attenuation
values are averaged to produce one less accurate pixel reading
the HU of 1 pixel is the average of what? - ANS all the data measurements within the pixel
how can we reduce the likelihood of volume averaging? - ANS by using smaller pixels
what determines pixel size? - ANS matrix size and the FOV
scan date = what? - ANS raw data
what does Raw data not have? - ANS does not have pixels and does not have HU assigned
either
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, what is reconstruction? - ANS the process of using raw data to create an image
what is image data? - ANS the data included in an image once each pixel is assigned a HU
Describe "Step and Shoot" machines - ANS 1) ~1980's
2) x-ray tube rotated 360deg around a pt to get a single slice
3) the motion of the x-ray tube was halted to advance the CT table
4) step and shoot happened b/c x-ray tube was connected to cables and would wind and
unwind
5) step and shoot aka: axial scanning, conventional scanning, serial scanning, sequence scanning
Describe "helical (spiral) scanning" - ANS 1) ~1990
2) no cables
3) enabled continuous gantry rotation
4) uninterrupted data acquisition that traces a helical path around the pt
Describe multidetector row CT - ANS 1) ~1992
2) more than 1 row of detectors so multiple slices could be obtained
the length and frequency of scans are determined in part by what? - ANS the x-ray tubes heat
capacity and heat dissipation rate
each detector cell is sampled and converted to a digital format by the what? - ANS DAS
each complete sample is called a "view"
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
TECHNOLOGISTS EXAM 2025/2026
QUESTIONS AND ANSWERS 100% PASS
What is spatial resolution? - ANS the ability of a system to define small objects distinctly
what is low-contrast resolution? - ANS the ability of a system to differentiate on the image
objects with similar densities
what is temporal resolution? - ANS the speed that the data can be acquired (high speed can
help eliminate motion artifacts)
what is the "z" axis? - ANS the thickness of the slice (plane)
what is the "x" axis? - ANS width
what is the "y" axis? - ANS height
what does the term "voxel" stand for? - ANS volume element
what is the most common matrix size? - ANS 512 x 512 (262,144)
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,what is attenuation? - ANS the degree to which the x-ray beam is reduced by an object
what determines the shades of gray on the image? - ANS the quantities of x-ray photons that
pass through the object and actually strike the detector
define density - ANS the mass of a substance per unit volume
the higher the density, the more opportunities for photon interaction
what is linear attenuation coefficient? (μ) - ANS the amount of x-ray beam that is scattered or
absorbed per unit thickness of the absorber
what is the linear attenuation coefficient for water? - ANS 0.18cm⁻¹
basically this means that 18% of x-ray beams are absorbed or scattered when they pass through
1 centimeter of water
the attenuation coefficient ___________ with increasing photon energy, and ___________ with
increasing atomic number & density - ANS decreases, increases
differences in linear attenuation coefficients are responsible for what? - ANS they are
responsible for x-ray image contrast
the values in CT images are sometimes referred to as ________ - ANS density
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,1 HU equals a ______% difference between the linear attenuation coefficient of the tissue as
compared with the linear attenuation coefficient of water - ANS 0.1%
beam-hardening artifacts - ANS artifacts that result from the preferential absorption of the
low-energy x-ray photons (leaving only the high intensity beams behind)
what type of artifact causes dark streaks and vague areas of decreased density? - ANS beam-
hardening artifacts
beam-hardening artifacts are aka? - ANS cupping artifacts
thicker CT slices increases the likelihood of what? - ANS missing very small objects
what is volume averaging? - ANS the process in CT by which different tissue attenuation
values are averaged to produce one less accurate pixel reading
the HU of 1 pixel is the average of what? - ANS all the data measurements within the pixel
how can we reduce the likelihood of volume averaging? - ANS by using smaller pixels
what determines pixel size? - ANS matrix size and the FOV
scan date = what? - ANS raw data
what does Raw data not have? - ANS does not have pixels and does not have HU assigned
either
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, what is reconstruction? - ANS the process of using raw data to create an image
what is image data? - ANS the data included in an image once each pixel is assigned a HU
Describe "Step and Shoot" machines - ANS 1) ~1980's
2) x-ray tube rotated 360deg around a pt to get a single slice
3) the motion of the x-ray tube was halted to advance the CT table
4) step and shoot happened b/c x-ray tube was connected to cables and would wind and
unwind
5) step and shoot aka: axial scanning, conventional scanning, serial scanning, sequence scanning
Describe "helical (spiral) scanning" - ANS 1) ~1990
2) no cables
3) enabled continuous gantry rotation
4) uninterrupted data acquisition that traces a helical path around the pt
Describe multidetector row CT - ANS 1) ~1992
2) more than 1 row of detectors so multiple slices could be obtained
the length and frequency of scans are determined in part by what? - ANS the x-ray tubes heat
capacity and heat dissipation rate
each detector cell is sampled and converted to a digital format by the what? - ANS DAS
each complete sample is called a "view"
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
