Radiography Exam Contrast Media and Pharmacology 2 — Questions and Answers

Question 1: Gadolinium-based contrast agents (GBCAs) are primarily used in which imaging modality?

Magnetic resonance imaging (MRI) (Correct answer)
Computed tomography (CT)
Conventional radiography
Nuclear medicine

Correct answer: Magnetic resonance imaging (MRI)

Gadolinium-based contrast agents are paramagnetic and used in MRI to shorten T1 relaxation times, producing bright enhancement on T1-weighted images.

GBCAs (e.g., gadobutrol, gadopentetate dimeglumine) are chelated gadolinium compounds that shorten T1 (and T2/T2*) relaxation times, increasing signal intensity on T1-weighted sequences. They are used for brain/spine tumor characterization, blood-brain barrier disruption, vessel imaging (MR angiography), cardiac MRI, and whole-body MRI. Nephrogenic systemic fibrosis (NSF) is a serious risk in patients with severe renal failure (eGFR <30), particularly with older linear GBCA formulations.

Question 2: The term 'contrast extravasation' refers to:

Leakage of IV contrast from the vein into surrounding soft tissue (Correct answer)
Allergic reaction to contrast media
Contrast entering the urinary collecting system
Contrast passing through the blood-brain barrier

Correct answer: Leakage of IV contrast from the vein into surrounding soft tissue

Contrast extravasation occurs when the IV needle or catheter is not properly positioned, allowing contrast to leak into the perivascular soft tissues rather than flowing into the vein.

Extravasation occurs in 0.1–0.9% of power injections. Small volumes (<10 mL) of nonionic low-osmolar contrast usually resolve without treatment. Large volumes, high-osmolar contrast, or injection near joints require elevation, cold compresses, and close monitoring. Compartment syndrome is a rare but serious complication. Power injectors with pressure limits and use of peripheral IV sites with good flow reduce extravasation risk. Documentation and patient follow-up are required.

Question 3: Which pharmacological agent is used to treat severe bronchospasm as part of a contrast reaction emergency?

Epinephrine (adrenaline) (Correct answer)
Atropine
Diphenhydramine
Metoprolol

Correct answer: Epinephrine (adrenaline)

Epinephrine is the drug of choice for anaphylaxis and severe bronchospasm because it causes bronchodilation (β2), vasoconstriction (α1), and positive cardiac effects to reverse anaphylaxis.

Epinephrine 1:1000 at 0.3 mg IM into the lateral thigh is the first-line treatment for anaphylaxis. Its β2-agonist effect causes bronchodilation, its α1 effect reverses hypotension, and its β1 effect supports cardiac output. Atropine is used for bradycardia/vagal reactions. Diphenhydramine treats urticaria but is inadequate alone for anaphylaxis. Inhaled β2-agonists (salbutamol) can supplement treatment for bronchospasm. Epinephrine can be repeated every 5–15 minutes as needed.

Question 4: The 'nephrogram phase' in contrast-enhanced CT occurs approximately how long after IV contrast injection?

80–120 seconds after injection (Correct answer)
25–35 seconds after injection
3–5 minutes after injection
10–15 minutes after injection

Correct answer: 80–120 seconds after injection

The nephrogram phase (also called the parenchymal phase) occurs 80–120 seconds after IV contrast injection when the renal cortex and medulla opacify uniformly as contrast is filtered by the nephrons.

CT contrast phases: Arterial phase (25–35s) — arteries opacify; Portal venous phase (60–80s) — liver, portal vein; Nephrogram/parenchymal phase (80–120s) — kidneys uniformly enhancing; Excretory/urographic phase (3–5 min+) — contrast in renal collecting system, ureters, bladder. Timing is crucial for renal masses, adrenal lesions, and urographic studies. Bolus tracking or test bolus techniques optimize contrast timing.

Question 5: Which patient condition requires the greatest caution and individualized risk-benefit assessment before administering iodinated IV contrast?

Chronic kidney disease with eGFR 20 mL/min/1.73m² (Correct answer)
Seasonal allergic rhinitis
Mild controlled asthma
History of previous mild urticaria from shellfish

Correct answer: Chronic kidney disease with eGFR 20 mL/min/1.73m²

An eGFR of 20 mL/min/1.73m² represents severe chronic kidney disease, placing the patient at significant risk for contrast-induced acute kidney injury and requiring careful risk-benefit evaluation.

Severe CKD (eGFR <30) is the most significant contraindication for iodinated IV contrast. Clinical risk-benefit analysis, hydration, use of minimum contrast volume, use of iso-osmolar contrast, and temporary nephrology consultation may be warranted. Seasonal rhinitis presents minimal risk. Mild asthma slightly increases risk (bronchospasm risk). Shellfish allergy is a myth as a predictor of contrast reaction — the relevant risk is a prior contrast reaction, not shellfish allergy.

Question 6: The concentration of iodinated contrast is expressed in mg of iodine per milliliter (mgI/mL). For a standard CT abdomen/pelvis using 350 mgI/mL contrast at a volume of 100 mL, what is the total iodine dose?

35,000 mg (35 g) of iodine (Correct answer)
35 mg of iodine
3,500 mg (3.5 g) of iodine
350,000 mg of iodine

Correct answer: 35,000 mg (35 g) of iodine

Total iodine dose = concentration × volume = 350 mgI/mL × 100 mL = 35,000 mg (35 grams) of iodine. This calculation is important for monitoring cumulative dose in multi-phase studies.

Total iodine load = mgI/mL × volume in mL. For 350 mgI/mL × 100 mL = 35,000 mgI = 35 g iodine. Typical adult CT doses range from 15–45 g iodine depending on the study. Higher iodine delivery rates (mgI/s = concentration × flow rate) correlate with better arterial opacification. Total iodine load is relevant for monitoring contrast nephrotoxicity risk and should be documented in the report.

Radiography Exam Contrast Media and Pharmacology 2

Gadolinium-based contrast agents (GBCAs) are primarily used in which imaging modality?