Computed Tomography Test Computed Tomography 3 — Questions and Answers
Question 1: Which phase of contrast enhancement is optimal for detecting hypervascular liver lesions such as hepatocellular carcinoma?
- Non-contrast phase
- Arterial phase (20–35 seconds post-injection) (Correct answer)
- Portal venous phase (60–70 seconds)
- Delayed equilibrium phase (3–5 minutes)
Correct answer: Arterial phase (20–35 seconds post-injection)
Hypervascular lesions like HCC receive predominantly arterial blood supply and enhance brightly relative to normal liver parenchyma during the arterial phase.
Question 2: What is the primary radiation protection principle that requires justifying each CT examination?
- ALARA
- Justification (Correct answer)
- Optimization
- Dose constraint
Correct answer: Justification
Justification is the ICRP principle requiring that no examination be performed unless the expected benefit exceeds the radiation detriment to the individual.
Question 3: In CT, what does 'z-axis resolution' refer to?
- In-plane pixel size in the axial plane
- Spatial resolution along the longitudinal (head-to-foot) axis of the patient (Correct answer)
- Contrast resolution between adjacent soft tissue structures
- Temporal resolution of the rotating gantry
Correct answer: Spatial resolution along the longitudinal (head-to-foot) axis of the patient
Z-axis (longitudinal) resolution determines the ability to distinguish structures stacked along the patient's long axis and improves with thinner collimation.
Question 4: Which CT scan parameter most directly controls the number of photons reaching the detector?
- kVp
- mAs (Correct answer)
- Gantry rotation time
- Reconstruction matrix size
Correct answer: mAs
mAs (milliampere-seconds) determines the total quantity of X-ray photons produced; doubling mAs doubles photon flux and roughly halves quantum noise.
Question 5: A patient receives 120 mL of iodinated contrast at 4 mL/s via antecubital IV. Which complication should the technologist monitor for immediately after injection?
- Contrast-induced nephropathy
- Delayed allergic reaction at 24 hours
- Acute contrast reaction including anaphylaxis (Correct answer)
- Radiation dermatitis
Correct answer: Acute contrast reaction including anaphylaxis
Acute adverse reactions including anaphylaxis can occur within minutes of IV iodinated contrast administration and require immediate recognition and intervention.
Question 6: What is the name of the CT artifact that appears as concentric rings centered on the isocenter?
- Beam hardening artifact
- Aliasing artifact
- Ring artifact (Correct answer)
- Partial volume artifact
Correct answer: Ring artifact
Ring artifacts are caused by defective or miscalibrated detector elements and manifest as circular bands centered on the gantry rotation axis.
Question 7: Which modality provides ionizing radiation-free cross-sectional imaging and is preferred for repeated abdominal follow-up in young patients?
- CT with low-dose protocol
- Positron emission tomography (PET)
- Magnetic resonance imaging (MRI) (Correct answer)
- Fluoroscopy
Correct answer: Magnetic resonance imaging (MRI)
MRI uses magnetic fields and radiofrequency pulses with no ionizing radiation, making it safer for serial follow-up imaging in young or pediatric populations.
Computed Tomography Test Computed Tomography 3
Which phase of contrast enhancement is optimal for detecting hypervascular liver lesions such as hepatocellular carcinoma?