Computed Tomography Test Computed Tomography Ultimate 5 — Questions and Answers
Question 1: What is the typical radiation dose range for a standard adult abdomen-pelvis CT examination?
- 0.1-0.5 mSv
- 1-3 mSv
- 8-15 mSv (Correct answer)
- 50-100 mSv
Correct answer: 8-15 mSv
A standard adult abdomen-pelvis CT delivers approximately 8-15 mSv effective dose, significantly higher than chest X-ray but providing much greater diagnostic information.
Question 2: Which reconstruction filter (kernel) would be most appropriate for evaluating fine bony detail in CT?
- Soft tissue kernel
- Standard kernel
- Sharp/bone kernel (Correct answer)
- Smoothing kernel
Correct answer: Sharp/bone kernel
Sharp or bone kernels enhance high-frequency information (edges) at the cost of increased noise, making fine bony trabecular and cortical detail more visible.
Question 3: What is the significance of the 'z-flying focal spot' technology in multidetector CT?
- It reduces gantry rotation time
- It doubles the number of effective slices by alternating focal spot positions along the z-axis (Correct answer)
- It eliminates beam hardening artifacts
- It allows dual-energy acquisitions
Correct answer: It doubles the number of effective slices by alternating focal spot positions along the z-axis
Z-flying focal spot alternates the focal spot between two positions along the z-axis within each rotation, doubling the number of independently acquired slices and improving z-axis resolution.
Question 4: A patient presents with an allergy to shellfish. What is the appropriate clinical management before administering iodinated contrast?
- Shellfish allergy is an absolute contraindication; cancel the study
- Shellfish allergy directly predicts iodinated contrast allergy; always premedicate
- Shellfish allergy alone is not a reliable predictor; assess for prior contrast reactions specifically (Correct answer)
- Double the contrast volume to overcome any allergic response
Correct answer: Shellfish allergy alone is not a reliable predictor; assess for prior contrast reactions specifically
Shellfish allergy is a common misconception as a predictor of contrast allergy; the true risk factor is a prior reaction to iodinated contrast media specifically.
Question 5: In CT perfusion imaging of the brain, which parameter best reflects the integrity of cerebral autoregulation?
- Cerebral blood volume (CBV) (Correct answer)
- Mean transit time (MTT)
- Time to peak (TTP)
- Cerebral blood flow (CBF)
Correct answer: Cerebral blood volume (CBV)
Cerebral blood volume (CBV) reflects the total volume of blood in a given brain region and is maintained by autoregulation; preserved CBV with reduced CBF indicates penumbral tissue.
Question 6: What is the primary advantage of using a low kVp technique in CT pulmonary angiography (CTPA)?
- Reduces scan time
- Increases contrast enhancement due to photoelectric effect near iodine's K-edge (Correct answer)
- Eliminates motion artifacts
- Improves bone detail visualization
Correct answer: Increases contrast enhancement due to photoelectric effect near iodine's K-edge
Lower kVp (e.g., 80-100 kVp) increases iodine conspicuity because the beam energy is closer to iodine's K-edge (~33 keV), enhancing the photoelectric effect and boosting contrast.
Question 7: Which parameter describes the relationship between table travel per gantry rotation and total beam collimation in helical CT?
- Duty cycle
- Pitch (Correct answer)
- Reconstruction interval
- Scan field of view
Correct answer: Pitch
Pitch is defined as table distance traveled per 360° rotation divided by the total nominal beam collimation width; values >1 indicate gaps in data and values <1 indicate overlap.
Computed Tomography Test Computed Tomography Ultimate 5
What is the typical radiation dose range for a standard adult abdomen-pelvis CT examination?