Storage of CT images in digital file format is referred to as soft copies. Hard copies of CT
images are those stored on laser film - ANS Soft copies of CT images are stored on which of the
following media?
1. hard drives
2. magnetic optical disk
3. laser film
Pre-patient collimation influences the slice thickness by reducing the size of the primary beam.
This is accomplished with the use of lead shutters that absorb the outer margins of the primary
beam. Increases in pre-patient collimation diminish patient radiation dose by reducing the
number of x-ray photons that reach the patient. - ANS For a single-slice CT (SSCT) system,
which of the following statements regarding pre-patient collimation is true?
1. An increase in pre-patient collimation increases patient radiation dose.
2. Pre-patient collimation is used to focus radiation through the section of interest.
3. Pre-patient collimation directly controls slice thickness.
Because of its high atomic number and relative stability, xenon gas is commonly used in gas
ionization CT detectors. - ANS Which of the following types of gas is commonly used for gas
ionization CT detectors?
0.29 mm × 0.29 mm × 1.0 mm.
The pixel dimension may be calculated by dividing the DFOV by the matrix size. This
two-dimensional pixel size is then multiplied by the length of the voxel. - ANS The image was
produced with a 1.0-mm aperture size and was displayed using a 5122 matrix and a 15-cm
DFOV. The voxel dimension for this image would be:
angle gantry around fillings
The only effective method of reducing streak artifact because of metal is to remove the metal
object(s) from the scanning field. In this case, the dental fillings cannot be removed, but the
gantry could be angled to avoid their interference. - ANS Which of the following steps could be
taken to reduce the artifact? See Fig.
1. Reduce section thickness.
2. Angle gantry around fillings.
3. Decrease kVp.
40cm
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