MRI MRI Contrast Agents 1 — Questions and Answers
Question 1: What is the mechanism of action of gadolinium-based contrast agents (GBCAs) in MRI?
- They directly emit radio waves that increase signal
- They shorten T1 relaxation time of nearby water protons, increasing signal on T1-weighted images (Correct answer)
- They increase T2 relaxation time, increasing signal on T2-weighted images
- They block radiofrequency pulses to create contrast
Correct answer: They shorten T1 relaxation time of nearby water protons, increasing signal on T1-weighted images
Gadolinium shortens the T1 relaxation time of surrounding water protons through dipole-dipole interactions, causing increased signal intensity on T1-weighted sequences.
Question 2: Nephrogenic Systemic Fibrosis (NSF) is a serious complication associated with GBCA administration in patients with:
- Liver failure
- Severe renal impairment (GFR <30 mL/min/1.73m²) (Correct answer)
- Active infection
- Allergy to iodine
Correct answer: Severe renal impairment (GFR <30 mL/min/1.73m²)
NSF occurs almost exclusively in patients with severe kidney disease (GFR <30) because impaired renal clearance prolongs gadolinium exposure, allowing transmetallation and tissue deposition.
Question 3: Which classification of GBCAs carries the LOWEST risk for NSF based on ACR guidance?
- Group I (linear ionic)
- Group II (linear non-ionic)
- Group III (macrocyclic) (Correct answer)
- All GBCAs carry equal NSF risk
Correct answer: Group III (macrocyclic)
Macrocyclic GBCAs (Group III) have a more stable cage-like structure that resists transmetallation and are associated with the lowest NSF risk.
Question 4: The standard dose of a non-specific extracellular GBCA for most MRI examinations is:
- 0.01 mmol/kg
- 0.05 mmol/kg
- 0.1 mmol/kg (Correct answer)
- 0.3 mmol/kg
Correct answer: 0.1 mmol/kg
The standard dose for most extracellular GBCAs is 0.1 mmol/kg body weight, which provides adequate contrast enhancement for most clinical applications.
Question 5: Which GBCA is approved by the FDA as a liver-specific agent taken up by hepatocytes?
- Gadobutrol (Gadavist)
- Gadoxetate disodium (Eovist/Primovist) (Correct answer)
- Gadopentetate dimeglumine (Magnevist)
- Gadobenate dimeglumine (MultiHance)
Correct answer: Gadoxetate disodium (Eovist/Primovist)
Gadoxetate disodium (Eovist in the US, Primovist in Europe) is taken up by functioning hepatocytes via OATP transporters, providing hepatobiliary phase imaging for liver lesion characterization.
Question 6: A patient reports a prior allergic-like reaction to a GBCA. Which of the following is the recommended premedication protocol?
- Antihistamine only, 1 hour before
- Corticosteroid + antihistamine, with the first steroid dose 13 hours before injection (Correct answer)
- Aspirin 24 hours before
- No premedication is effective for GBCA reactions
Correct answer: Corticosteroid + antihistamine, with the first steroid dose 13 hours before injection
The ACR-recommended premedication protocol for prior GBCA reactions includes corticosteroids given 13, 7, and 1 hour before contrast, combined with an antihistamine 1 hour before.
MRI MRI Contrast Agents 1
What is the mechanism of action of gadolinium-based contrast agents (GBCAs) in MRI?