Computed Tomography Test Computed Tomography (CT) 3 — Questions and Answers
Question 1: Which type of CT artifact appears as alternating dark and bright bands radiating from high-density objects like metal implants?
- Beam hardening artifact (Correct answer)
- Partial volume artifact
- Ring artifact
- Motion artifact
Correct answer: Beam hardening artifact
Beam hardening occurs when lower-energy photons are preferentially absorbed by dense materials, causing streaks or dark bands near metal or bone.
Question 2: In CT, what does the Hounsfield unit (HU) value of approximately -100 indicate?
- Air
- Fat (Correct answer)
- Water
- Soft tissue
Correct answer: Fat
Fat typically measures between -50 and -150 HU, with approximately -100 HU being a classic fat attenuation value, while air is near -1000 HU.
Question 3: What is the primary indication for CT perfusion imaging of the brain?
- Detection of intracranial hemorrhage
- Assessment of cerebrovascular ischemia and infarct core vs. penumbra (Correct answer)
- Diagnosis of brain tumors
- Evaluation of skull fractures
Correct answer: Assessment of cerebrovascular ischemia and infarct core vs. penumbra
CT perfusion maps cerebral blood flow, blood volume, and mean transit time to differentiate irreversibly infarcted tissue from salvageable ischemic penumbra in acute stroke.
Question 4: Which oral contrast agent is preferred in CT when bowel perforation is suspected?
- Barium sulfate
- Water-soluble iodinated contrast (e.g., Gastrografin) (Correct answer)
- Negative contrast (water only)
- No oral contrast is needed
Correct answer: Water-soluble iodinated contrast (e.g., Gastrografin)
Water-soluble iodinated agents are used when perforation is suspected because barium leaking into the peritoneum causes severe peritonitis.
Question 5: What is the normal attenuation range (HU) for the liver parenchyma on a non-contrast CT?
- 0 to 20 HU
- 20 to 40 HU
- 50 to 70 HU (Correct answer)
- 80 to 100 HU
Correct answer: 50 to 70 HU
Normal liver parenchyma measures approximately 50–70 HU on non-contrast CT, slightly higher than the spleen under normal conditions.
Question 6: What does 'window width' control in CT image display?
- The brightness of the display
- The range of HU values displayed as shades of gray (Correct answer)
- The spatial resolution of the image
- The slice thickness
Correct answer: The range of HU values displayed as shades of gray
Window width determines the range of Hounsfield units mapped to the grayscale display; a narrow width increases contrast, while a wide width shows a broader density range.
Question 7: During a dual-energy CT scan, what primary advantage does dual-energy provide over single-energy CT?
- Faster image acquisition
- Material differentiation and virtual non-contrast imaging (Correct answer)
- Lower radiation dose in all cases
- Improved temporal resolution
Correct answer: Material differentiation and virtual non-contrast imaging
Dual-energy CT acquires data at two different kVp settings, enabling material decomposition to distinguish iodine, calcium, and uric acid, and to create virtual non-contrast images.
Computed Tomography Test Computed Tomography (CT) 3
Which type of CT artifact appears as alternating dark and bright bands radiating from high-density objects like metal implants?