1. Computed Tomography Q & A
Phillip W Patton, Ph.D.

2. B. Back-projection algorithm C. Tomographic slice D. Primary beam
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

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

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

5. D. Section thickness does not directly affect x-ray heat loading.
2) Answer
D. Section thickness does not directly affect x-ray heat loading.

6. A. HU of blood vessels B. Required kVp C. Required mA D. Patient dose
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

7. 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.

8. A. Variable for different section thicknesses
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

9. 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

10. 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

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

12. 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

13. 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.