Computed Tomography Q & A

Phillip W Patton, Ph.D.

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

1) Answer

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

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

2) Answer

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

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

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.

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

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

5) The CT image display contrast

A. Must be selected prior to the x-ray exposuresB. May be altered after the CT scanC. Does not modify the appearance of the CT image D. Can be used to change the HU values of image dataE. None of the above

5) Answer

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

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

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.