COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is spatial resolution? - (ANSWER)the ability of a system to define small objects distinctly
what is low-contrast resolution? - (ANSWER)the ability of a system to differentiate on the image objects
with similar densities
what is temporal resolution? - (ANSWER)the speed that the data can be acquired (high speed can help
eliminate motion artifacts)
what is the "z" axis? - (ANSWER)the thickness of the slice (plane)
what is the "x" axis? - (ANSWER)width
what is the "y" axis? - (ANSWER)height
what does the term "voxel" stand for? - (ANSWER)volume element
what is the most common matrix size? - (ANSWER)512 x 512 (262,144)
what is attenuation? - (ANSWER)the degree to which the x-ray beam is reduced by an object
what determines the shades of gray on the image? - (ANSWER)the quantities of x-ray photons that pass
through the object and actually strike the detector
define density - (ANSWER)the mass of a substance per unit volume
the higher the density, the more opportunities for photon interaction
,COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is linear attenuation coefficient? (μ) - (ANSWER)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? - (ANSWER)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 - (ANSWER)decreases, increases
differences in linear attenuation coefficients are responsible for what? - (ANSWER)they are responsible
for x-ray image contrast
the values in CT images are sometimes referred to as ________ - (ANSWER)density
1 HU equals a ______% difference between the linear attenuation coefficient of the tissue as compared
with the linear attenuation coefficient of water - (ANSWER)0.1%
beam-hardening artifacts - (ANSWER)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? - (ANSWER)beam-
hardening artifacts
beam-hardening artifacts are aka? - (ANSWER)cupping artifacts
thicker CT slices increases the likelihood of what? - (ANSWER)missing very small objects
,COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is volume averaging? - (ANSWER)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? - (ANSWER)all the data measurements within the pixel
how can we reduce the likelihood of volume averaging? - (ANSWER)by using smaller pixels
what determines pixel size? - (ANSWER)matrix size and the FOV
scan date = what? - (ANSWER)raw data
what does Raw data not have? - (ANSWER)does not have pixels and does not have HU assigned either
what is reconstruction? - (ANSWER)the process of using raw data to create an image
what is image data? - (ANSWER)the data included in an image once each pixel is assigned a HU
Describe "Step and Shoot" machines - (ANSWER)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" - (ANSWER)1) ~1990
2) no cables
3) enabled continuous gantry rotation
4) uninterrupted data acquisition that traces a helical path around the pt
, COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
Describe multidetector row CT - (ANSWER)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? - (ANSWER)the x-ray tubes heat
capacity and heat dissipation rate
each detector cell is sampled and converted to a digital format by the what? - (ANSWER)DAS
each complete sample is called a "view"
what does the reconstruction processor do? - (ANSWER)it takes the individual views and reconstructs
the densities within the slice
what are the 3 main phases of a CT scan? - (ANSWER)1) data acquisition
2) image reconstruction
3) image display
what's the average gantry tilt range for most scanners? - (ANSWER)+/- 15 to +/- 30
how do slip rings work? - (ANSWER)they use a brush-like apparatus to provide continuous electrical
power and electronic communication across a rotating surface
slip rings permit the gantry frame to rotate continuously
slip rings make helical scans possible
where is the high frequency generator located? - (ANSWER)within the gantry
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is spatial resolution? - (ANSWER)the ability of a system to define small objects distinctly
what is low-contrast resolution? - (ANSWER)the ability of a system to differentiate on the image objects
with similar densities
what is temporal resolution? - (ANSWER)the speed that the data can be acquired (high speed can help
eliminate motion artifacts)
what is the "z" axis? - (ANSWER)the thickness of the slice (plane)
what is the "x" axis? - (ANSWER)width
what is the "y" axis? - (ANSWER)height
what does the term "voxel" stand for? - (ANSWER)volume element
what is the most common matrix size? - (ANSWER)512 x 512 (262,144)
what is attenuation? - (ANSWER)the degree to which the x-ray beam is reduced by an object
what determines the shades of gray on the image? - (ANSWER)the quantities of x-ray photons that pass
through the object and actually strike the detector
define density - (ANSWER)the mass of a substance per unit volume
the higher the density, the more opportunities for photon interaction
,COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is linear attenuation coefficient? (μ) - (ANSWER)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? - (ANSWER)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 - (ANSWER)decreases, increases
differences in linear attenuation coefficients are responsible for what? - (ANSWER)they are responsible
for x-ray image contrast
the values in CT images are sometimes referred to as ________ - (ANSWER)density
1 HU equals a ______% difference between the linear attenuation coefficient of the tissue as compared
with the linear attenuation coefficient of water - (ANSWER)0.1%
beam-hardening artifacts - (ANSWER)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? - (ANSWER)beam-
hardening artifacts
beam-hardening artifacts are aka? - (ANSWER)cupping artifacts
thicker CT slices increases the likelihood of what? - (ANSWER)missing very small objects
,COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
what is volume averaging? - (ANSWER)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? - (ANSWER)all the data measurements within the pixel
how can we reduce the likelihood of volume averaging? - (ANSWER)by using smaller pixels
what determines pixel size? - (ANSWER)matrix size and the FOV
scan date = what? - (ANSWER)raw data
what does Raw data not have? - (ANSWER)does not have pixels and does not have HU assigned either
what is reconstruction? - (ANSWER)the process of using raw data to create an image
what is image data? - (ANSWER)the data included in an image once each pixel is assigned a HU
Describe "Step and Shoot" machines - (ANSWER)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" - (ANSWER)1) ~1990
2) no cables
3) enabled continuous gantry rotation
4) uninterrupted data acquisition that traces a helical path around the pt
, COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM REVIEW
QUESTIONS & ANSWERS RATED 100% CORRECT!!
Describe multidetector row CT - (ANSWER)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? - (ANSWER)the x-ray tubes heat
capacity and heat dissipation rate
each detector cell is sampled and converted to a digital format by the what? - (ANSWER)DAS
each complete sample is called a "view"
what does the reconstruction processor do? - (ANSWER)it takes the individual views and reconstructs
the densities within the slice
what are the 3 main phases of a CT scan? - (ANSWER)1) data acquisition
2) image reconstruction
3) image display
what's the average gantry tilt range for most scanners? - (ANSWER)+/- 15 to +/- 30
how do slip rings work? - (ANSWER)they use a brush-like apparatus to provide continuous electrical
power and electronic communication across a rotating surface
slip rings permit the gantry frame to rotate continuously
slip rings make helical scans possible
where is the high frequency generator located? - (ANSWER)within the gantry
