Computed Tomography Test Computed Tomography (CT) 5 — Questions and Answers
Question 1: Which structure is best evaluated using a 'brain window' setting (W:80, L:40)?
- Pulmonary nodules
- Gray-white matter differentiation in the brain (Correct answer)
- Cortical bone fractures
- Liver lesions
Correct answer: Gray-white matter differentiation in the brain
A narrow window width centered around 40 HU maximizes contrast between gray matter (~40 HU) and white matter (~30 HU), essential for evaluating brain parenchyma.
Question 2: What is the primary advantage of iterative reconstruction over filtered back projection (FBP) in CT?
- Shorter reconstruction time
- Reduced image noise at equivalent or lower radiation dose (Correct answer)
- Higher spatial resolution
- Fewer beam hardening artifacts
Correct answer: Reduced image noise at equivalent or lower radiation dose
Iterative reconstruction algorithms model the imaging process and iteratively reduce noise, allowing diagnostic quality images at lower mAs and reduced patient dose compared to FBP.
Question 3: A CT scan shows a pulmonary nodule measuring 6 mm in a high-risk patient. Per Fleischner Society guidelines, what is the recommended follow-up?
- No follow-up needed
- CT at 6–12 months, then consider CT at 18–24 months (Correct answer)
- Immediate PET-CT
- Biopsy within 1 month
Correct answer: CT at 6–12 months, then consider CT at 18–24 months
Fleischner Society guidelines recommend CT follow-up at 6–12 months for a 6 mm solid nodule in high-risk patients (smoker, prior cancer), with possible additional follow-up.
Question 4: What does 'temporal resolution' mean in cardiac CT?
- The time required to reconstruct images after scanning
- The minimum time interval the scanner needs to freeze cardiac motion (Correct answer)
- The speed of the contrast bolus through the heart
- The number of cardiac phases reconstructed
Correct answer: The minimum time interval the scanner needs to freeze cardiac motion
Temporal resolution in cardiac CT refers to the shortest acquisition time (typically half the gantry rotation time) needed to capture a sharp, motion-free image of the moving heart.
Question 5: During a CT scan, the technologist notices the patient's heart rate is 85 bpm for a cardiac CT. What is the most appropriate action?
- Proceed without any intervention
- Administer beta-blocker medication to lower heart rate below 60 bpm if not contraindicated (Correct answer)
- Increase the kVp to compensate
- Switch to a 64-slice scanner
Correct answer: Administer beta-blocker medication to lower heart rate below 60 bpm if not contraindicated
Heart rates above 65–70 bpm degrade cardiac CT image quality due to motion; beta-blockers are administered (when not contraindicated) to achieve a slower, steadier rate.
Question 6: What is the primary use of saline flush immediately following IV contrast injection in CT?
- To dilute contrast in the kidneys and reduce nephrotoxicity
- To push the contrast bolus forward and improve vascular opacification while reducing contrast volume (Correct answer)
- To cool the injector tubing
- To prevent extravasation
Correct answer: To push the contrast bolus forward and improve vascular opacification while reducing contrast volume
A saline chase pushes residual contrast from the tubing and peripheral veins into circulation, extending the bolus and improving opacification with less total contrast.
Question 7: On a CT scan of the abdomen, what Hounsfield unit threshold is typically used to identify an acute hemorrhage?
- 0–20 HU
- 20–40 HU
- 40–60 HU
- 55–80 HU (Correct answer)
Correct answer: 55–80 HU
Acute hemorrhage typically measures 55–80 HU on non-contrast CT due to the high protein content of clotted blood, making it hyperdense relative to surrounding soft tissues.
Computed Tomography Test Computed Tomography (CT) 5
Which structure is best evaluated using a 'brain window' setting (W:80, L:40)?