ARRT CT Physics 2

Question 1

What is the primary purpose of the bow-tie filter in a CT scanner?

Accepted Answer

Compensate for the cylindrical shape of patients to reduce peripheral dose

Answer

The bow-tie (wedge) filter shapes the beam so less radiation hits the thinner periphery of the patient, reducing dose and preventing detector saturation.

Question 2

In CT, the term 'pitch' for single-slice CT is calculated as:

Accepted Answer

Table feed per rotation / slice thickness

Answer

Pitch = table feed per 360° rotation divided by the nominal slice thickness; a pitch >1 means gaps exist between consecutive slices.

Question 3

Which artifact appears as bright or dark bands radiating from high-density structures like metal implants?

Accepted Answer

Streak artifact

Answer

Streak artifacts arise from highly attenuating objects (metal, dense bone) causing inconsistent projections that reconstruct as linear streaks.

Question 4

What does the term 'half-scan reconstruction' refer to in CT?

Accepted Answer

Using 180° + fan angle of data instead of a full 360° to reduce motion artifact

Answer

Half-scan reconstruction uses approximately 180° + fan beam angle of data, which can reduce cardiac or other motion artifacts by shortening effective scan time.

Question 5

The spatial resolution of a CT image is primarily limited by which factor?

Accepted Answer

Focal spot size and detector aperture

Answer

Focal spot size and detector cell aperture are the primary hardware factors limiting spatial resolution in CT.

(ARRT) American Registry of Radiologic Technologists Computed Tomography Certification Practice Test

(ARRT) American Registry of Radiologic Technologists Computed Tomography Certification Practice Test

ARRT CT Physics 2