Computed Tomography Questions with
Accurate Answers
1/r blur and deconvolution illustrations correct answer
Adaptive beam collimation image correct answer
Advantages/drawbacks to Dual-Source DECT correct answer Smaller Tube B FOV,
which limits FOV of dual-energy reconstruction. Also b/c both imaging chains are
active during acq., scatter from one imaging chains impacts the other and
requires correction techniques, which ultimate result in more noise. However,
more filtration can be added to the higher kV source, which increases energy
separation and improves the energy subtraction.
All modern multidetector array CT scanners use ____ solid state detectors correct
answer indirect (scintillating)
Angular mA modulation image correct answer
Approximate fan angle of most CT scanners correct answer 60 degrees
As the scan setting of a CT scatter is increased from 120-140 kVp, the CS is
changed by about ____% correct answer ~-5%
Axial CT Scanning Diagram correct answer
Beam Hardening Artifact Illustration correct answer
,Beam hardening spectrum illustration correct answer
Benefits/trade-offs of CT imaging with a wide cone angle (~10 deg, 16 cm Z-axis
coverage) correct answer Whole organ imaging can be achieved without table
motion, such as CT angiography, perfusion studies (head, kidneys, heart, etc).
There is also increased x-ray scatter and cone beam artifacts
Bowtie Dose Distribution Diagram correct answer
Bowtie Filter Diagrams correct answer
Bowtie Filter Photograph correct answer
Caveat for reducing pitch correct answer Some scanners may adjust other
parameters besides pitch to maintain constant CTDIvol
Caveat for shortening tube rotation time to reduce dose correct answer Some
scanners may compensate for changes in rotation time with adjustments to pitch
or mA in order to keep the mA per rotation constant
• CTDI may not change in the expected manner
• Varies by manufacturer and software version
Compton Scatter Coefficient Proportionality correct answer where rho is the mass
density of the tissue in a voxel, N is Avogadro's number, Z is the atomic number,
and A is the atomic mass.
, Cone beam reconstruction correct answer Similar to fan beam reconstruction
algorithms, but they keep track of the beam divergence in the z-direction (Cone
angle). Basic cone beam reconstruction process is Feldkampt algorithm (FDK).
Cone beam recon. violates mathematical requirements for sampling Fourier
space, and for extreme cone beam used in flat panels or other very wide CBCT
systems, this can lean to cone beam artifacts
Cone-beam artifacts correct answer Caused by undersampling in the cone angle
dimension (z) and in Fourier space, can be reduced with smaller cone angle
Contiguous axial CT scan beam profile diagram correct answer
CT Adaptive Beam Collimation correct answer The process of removing wasted
beam with collimation when overscanning for helical image acquisition
CT Adaptive Beam Collimator Photos correct answer
CT Aliasing Artifact correct answer Caused by sharp bone edges or metal implant.
To reduce, increase sampling rate (flying focal spot) or use low cut-off
reconstruction kernel (smooth kernel)
CT Angiography correct answer CT has higher contrast resolution than traditional
angiography and consequently requires only venous access as opposed to more
invasive arterial access for fluoroscopy-based angiography. CTA is really just
contrast-enhanced CT where the images have been processed to highlight the
vascular anatomy using image processing techniques. In general maximum
intensity projection procedures produce excellent CTA images (may use
pseudocolor as well)
Accurate Answers
1/r blur and deconvolution illustrations correct answer
Adaptive beam collimation image correct answer
Advantages/drawbacks to Dual-Source DECT correct answer Smaller Tube B FOV,
which limits FOV of dual-energy reconstruction. Also b/c both imaging chains are
active during acq., scatter from one imaging chains impacts the other and
requires correction techniques, which ultimate result in more noise. However,
more filtration can be added to the higher kV source, which increases energy
separation and improves the energy subtraction.
All modern multidetector array CT scanners use ____ solid state detectors correct
answer indirect (scintillating)
Angular mA modulation image correct answer
Approximate fan angle of most CT scanners correct answer 60 degrees
As the scan setting of a CT scatter is increased from 120-140 kVp, the CS is
changed by about ____% correct answer ~-5%
Axial CT Scanning Diagram correct answer
Beam Hardening Artifact Illustration correct answer
,Beam hardening spectrum illustration correct answer
Benefits/trade-offs of CT imaging with a wide cone angle (~10 deg, 16 cm Z-axis
coverage) correct answer Whole organ imaging can be achieved without table
motion, such as CT angiography, perfusion studies (head, kidneys, heart, etc).
There is also increased x-ray scatter and cone beam artifacts
Bowtie Dose Distribution Diagram correct answer
Bowtie Filter Diagrams correct answer
Bowtie Filter Photograph correct answer
Caveat for reducing pitch correct answer Some scanners may adjust other
parameters besides pitch to maintain constant CTDIvol
Caveat for shortening tube rotation time to reduce dose correct answer Some
scanners may compensate for changes in rotation time with adjustments to pitch
or mA in order to keep the mA per rotation constant
• CTDI may not change in the expected manner
• Varies by manufacturer and software version
Compton Scatter Coefficient Proportionality correct answer where rho is the mass
density of the tissue in a voxel, N is Avogadro's number, Z is the atomic number,
and A is the atomic mass.
, Cone beam reconstruction correct answer Similar to fan beam reconstruction
algorithms, but they keep track of the beam divergence in the z-direction (Cone
angle). Basic cone beam reconstruction process is Feldkampt algorithm (FDK).
Cone beam recon. violates mathematical requirements for sampling Fourier
space, and for extreme cone beam used in flat panels or other very wide CBCT
systems, this can lean to cone beam artifacts
Cone-beam artifacts correct answer Caused by undersampling in the cone angle
dimension (z) and in Fourier space, can be reduced with smaller cone angle
Contiguous axial CT scan beam profile diagram correct answer
CT Adaptive Beam Collimation correct answer The process of removing wasted
beam with collimation when overscanning for helical image acquisition
CT Adaptive Beam Collimator Photos correct answer
CT Aliasing Artifact correct answer Caused by sharp bone edges or metal implant.
To reduce, increase sampling rate (flying focal spot) or use low cut-off
reconstruction kernel (smooth kernel)
CT Angiography correct answer CT has higher contrast resolution than traditional
angiography and consequently requires only venous access as opposed to more
invasive arterial access for fluoroscopy-based angiography. CTA is really just
contrast-enhanced CT where the images have been processed to highlight the
vascular anatomy using image processing techniques. In general maximum
intensity projection procedures produce excellent CTA images (may use
pseudocolor as well)
