Computed Tomography Test CT Contrast Media and Patient Preparation 1 — Questions and Answers
Question 1: What is the most common type of iodinated contrast media used for CT examinations?
- Non-ionic, water-soluble iodinated contrast (Correct answer)
- Barium sulfate suspension
- Ionic high-osmolar contrast
- Gadolinium-based contrast
Correct answer: Non-ionic, water-soluble iodinated contrast
Non-ionic, water-soluble iodinated contrast agents are preferred for CT because they have lower osmolality and fewer adverse reactions compared to ionic agents.
Question 2: Which serum creatinine-based calculation is most commonly used to screen for contrast-induced nephropathy risk before CT?
- eGFR (estimated Glomerular Filtration Rate) (Correct answer)
- BUN/creatinine ratio
- Urine specific gravity
- Creatinine clearance via timed urine collection
Correct answer: eGFR (estimated Glomerular Filtration Rate)
eGFR calculated from serum creatinine is the standard screening tool; an eGFR <30 mL/min/1.73m² generally indicates high risk for contrast nephrotoxicity.
Question 3: At what injection rate (mL/sec) is intravenous contrast typically administered for a CT pulmonary angiography (CTPA)?
- 3–5 mL/sec (Correct answer)
- 0.5–1 mL/sec
- 10–15 mL/sec
- Less than 0.5 mL/sec
Correct answer: 3–5 mL/sec
CTPA requires a brisk injection rate of 3–5 mL/sec to achieve adequate pulmonary artery opacification during the brief arterial phase.
Question 4: Which medication must be withheld 48 hours before and after iodinated contrast administration in patients with renal impairment?
- Metformin (Correct answer)
- Aspirin
- Lisinopril
- Atorvastatin
Correct answer: Metformin
Metformin must be withheld because contrast-induced nephropathy can impair its renal clearance, leading to toxic accumulation and risk of lactic acidosis.
Question 5: What is the typical oral contrast agent used to opacify the GI tract during abdominal CT?
- Dilute barium or water-soluble iodinated contrast (Correct answer)
- Gadolinium
- Iohexol injection
- Normal saline
Correct answer: Dilute barium or water-soluble iodinated contrast
Dilute barium sulfate or water-soluble iodinated contrast is given orally to distend and opacify the bowel, distinguishing it from adjacent pathology.
Question 6: Which phase of contrast enhancement is best for evaluating hypervascular liver tumors such as hepatocellular carcinoma (HCC)?
- Arterial phase (25–35 seconds post-injection) (Correct answer)
- Portal venous phase (60–70 seconds)
- Delayed phase (3–5 minutes)
- Non-contrast phase
Correct answer: Arterial phase (25–35 seconds post-injection)
HCC derives its blood supply primarily from the hepatic artery and enhances dramatically during the arterial phase, a hallmark feature used for diagnosis.
Computed Tomography Test CT Contrast Media and Patient Preparation 1
What is the most common type of iodinated contrast media used for CT examinations?