Computed Tomography Test Computed Tomography Ultimate 4 — Questions and Answers
Question 1: What is the purpose of 'prospective triggering' in cardiac CT?
- To scan continuously throughout the cardiac cycle
- To acquire data only during a specific, predetermined phase of the cardiac cycle (Correct answer)
- To automatically adjust kVp based on heart rate
- To reconstruct multiple cardiac phases from one acquisition
Correct answer: To acquire data only during a specific, predetermined phase of the cardiac cycle
Prospective triggering uses the ECG signal to trigger X-ray exposure only during a specific quiescent phase, significantly reducing radiation dose compared to retrospective gating.
Question 2: Which ionizing radiation unit is used to express the effective dose that accounts for tissue radiosensitivity?
- Gray (Gy)
- Sievert (Sv) (Correct answer)
- Roentgen (R)
- Rad
Correct answer: Sievert (Sv)
The Sievert (Sv) is used to express effective dose, which weights absorbed dose by tissue-specific radiation sensitivity and radiation type weighting factors.
Question 3: In CT angiography, what is the bolus tracking technique used for?
- Reducing the volume of contrast needed
- Triggering the diagnostic scan when contrast reaches the target vessel (Correct answer)
- Measuring blood flow velocity
- Calculating vessel diameter automatically
Correct answer: Triggering the diagnostic scan when contrast reaches the target vessel
Bolus tracking monitors contrast enhancement in a target vessel using repeated low-dose images and automatically triggers the diagnostic scan when the preset HU threshold is reached.
Question 4: What is the main disadvantage of increasing pitch in helical CT?
- Increased radiation dose
- Reduced z-axis resolution (Correct answer)
- Longer scan time
- Decreased detector coverage
Correct answer: Reduced z-axis resolution
Higher pitch values interpolate data across a wider z-axis distance, which degrades longitudinal (z-axis) spatial resolution and can increase image noise.
Question 5: What type of CT artifact is caused by patient movement during data acquisition?
- Ring artifact
- Star artifact
- Motion artifact (Correct answer)
- Cupping artifact
Correct answer: Motion artifact
Motion artifacts appear as blurring, streaks, or ghosting on images when the patient moves during the scan, causing inconsistent projection data.
Question 6: Which window setting is most appropriate for evaluating pulmonary nodules on chest CT?
- Soft tissue window (W:400, L:40)
- Lung window (W:1500, L:-600) (Correct answer)
- Bone window (W:2000, L:500)
- Brain window (W:80, L:35)
Correct answer: Lung window (W:1500, L:-600)
Lung window settings use a wide window width and low center level to display the full dynamic range of pulmonary parenchyma including subtle nodules and airways.
Question 7: What is the primary determinant of contrast-to-noise ratio (CNR) in CT imaging?
- Reconstruction kernel
- Radiation dose (Correct answer)
- Field of view
- Gantry rotation speed
Correct answer: Radiation dose
Radiation dose is the primary determinant of CNR because higher dose reduces quantum noise, making differences in tissue attenuation more detectable.
Computed Tomography Test Computed Tomography Ultimate 4
What is the purpose of 'prospective triggering' in cardiac CT?