MRI MRI Contrast Agents 2 — Questions and Answers
Question 1: Gadolinium retention in the brain has been observed particularly in which structure on unenhanced T1-weighted images in patients receiving multiple GBCA doses?
- Hippocampus
- Dentate nucleus of the cerebellum (Correct answer)
- Thalamus
- Caudate nucleus
Correct answer: Dentate nucleus of the cerebellum
Gadolinium deposition in the dentate nucleus and globus pallidus manifests as T1 hyperintensity on unenhanced brain MRI after multiple GBCA administrations.
Question 2: Which of the following best describes a blood-pool GBCA used in MR angiography?
- It remains exclusively in the arterial system
- It binds reversibly to albumin, prolonging intravascular residence time (Correct answer)
- It distributes only in hepatic tissue
- It crosses the blood-brain barrier
Correct answer: It binds reversibly to albumin, prolonging intravascular residence time
Blood-pool agents (e.g., gadofosveset) bind reversibly to albumin, extending their half-life in the vascular space and allowing steady-state MRA over a longer acquisition window.
Question 3: For a contrast-enhanced MRA of the aorta, the bolus tracking technique monitors contrast arrival in which vessel to trigger the 3D acquisition?
- Superior mesenteric artery
- Abdominal aorta or descending thoracic aorta at the level of interest (Correct answer)
- Right atrium
- Femoral artery
Correct answer: Abdominal aorta or descending thoracic aorta at the level of interest
A monitoring slice is placed at the aorta at the target level; when the contrast bolus arrives (signal threshold), the 3D acquisition is automatically triggered.
Question 4: Which of the following is the correct management for a patient who experiences an acute severe allergic-like reaction (anaphylaxis) following GBCA injection?
- Administer oral Benadryl and observe for 15 minutes
- Stop contrast injection, call code team, administer epinephrine 0.3 mg IM (1:1000) (Correct answer)
- Administer 50 mg IV diphenhydramine and continue scan
- Administer IV saline bolus only
Correct answer: Stop contrast injection, call code team, administer epinephrine 0.3 mg IM (1:1000)
Anaphylaxis requires immediate cessation of injection, emergency team activation, and epinephrine 0.3 mg IM (1:1000 concentration) in the lateral thigh as first-line treatment.
Question 5: What is the primary advantage of using a higher-relaxivity GBCA (e.g., gadobenate dimeglumine) compared to a standard-relaxivity agent?
- It can be used at a lower dose to achieve comparable enhancement (Correct answer)
- It is completely renally safe at any dose
- It eliminates the need for dynamic imaging
- It crosses the blood-brain barrier more readily
Correct answer: It can be used at a lower dose to achieve comparable enhancement
Higher relaxivity means greater T1 shortening per unit concentration, so a lower molar dose can produce equivalent or superior enhancement compared to standard agents.
Question 6: The term 'T1 mapping' in cardiac MRI using gadolinium is used to quantify which clinically important tissue property?
- Myocardial perfusion rate
- Extracellular volume fraction (ECV) as a marker of fibrosis (Correct answer)
- Ejection fraction
- Coronary artery stenosis grade
Correct answer: Extracellular volume fraction (ECV) as a marker of fibrosis
Pre- and post-contrast T1 mapping allows calculation of the extracellular volume (ECV), which is an established quantitative biomarker of diffuse myocardial fibrosis.
