Computed%20Tomography%20Q%20

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Computed Tomography Q A

• Phillip W Patton, Ph.D.

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1) The measured x-ray transmissions from a single
CT fan beam through a patient is called a

• A. Filter
• B. Back-projection algorithm
• C. Tomographic slice
• D. Primary beam
• E. Projection

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1) Answer

• E. A projection is a profile of transmitted x-ray
  intensities through the patient at any given
  location of the tube.

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2) Anode heat loading on a CT x-ray tube
increases with all the following EXCEPT

• A. kV
• B. mA
• C. Scan time
• D. Section thickness
• E. Number of sections

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2) Answer

• D. Section thickness does not directly affect
  x-ray heat loading.

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3) Use of intravascular contrast when performing
a single CT section will significantly increase
the

• A. HU of blood vessels
• B. Required kVp
• C. Required mA
• D. Patient dose
• E. Image noise

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3) Answer

• A. Intravenous contrast increases the density and
  atomic number of blood and tissues. This
  increases x-ray attenuation and thereby the
  resultant HU value.

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4) CT collimators are

• A. Variable for different section thicknesses
• B. Not necessary for helical scans
• C. Usually made out of plexiglass
• D. Bow-tie shaped
• E. Cooled using fans

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4) Answer

• A. The collimators are located at the x-ray tube
  and have a variable width (1 to 10 mm), which
  defines the CT section thickness

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5) The CT image display contrast

• A. Must be selected prior to the x-ray exposures
• B. May be altered after the CT scan
• C. Does not modify the appearance of the CT image
  
• D. Can be used to change the HU values of image
  data
• E. None of the above

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5) Answer

• B. Changing the display contrast alters the
  appearance of the CT image, but not the
  reconstructed image data.

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6) Partial volume artifacts in CT are generally
reduced when

• A. Section thickness increases
• B. Scanning time is increased
• C. Image matrix size increases
• D. Fifth-generation scanners are used
• E. Small focal spot sizes are used

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6) Answer

• C. a larger image matrix size improves spatial
  resolution and hence is likely to reduce volume
  averaging known as the partial volume effect.