Can a Magnetic Resonance Angiography (MRA) harm the kidneys?

Kidney Safety Concerns with MRA

MRA itself does not harm the kidneys, but gadolinium-based contrast agents used in contrast-enhanced MRA can cause nephrogenic systemic fibrosis (NSF) in patients with severe renal impairment (GFR <30 mL/min/1.73 m²). 1

Safety Profile of MRA

MRA as an imaging technique is very safe with no short or long-term ill effects at current field strengths (≤3 T). The primary safety concerns with MRA include:

• Claustrophobia (occurs in 3-7% of patients)
• Risk of ferromagnetic objects becoming projectiles
• Contraindications for patients with certain electronic implants 1

Contrast-Enhanced MRA and Kidney Risk

Gadolinium-Based Contrast Agents and NSF

The primary kidney-related risk with MRA comes from gadolinium-based contrast agents used in contrast-enhanced MRA:

• NSF risk is significantly increased in patients with:

  • Acute or chronic severe renal insufficiency (GFR <30 mL/min/1.73 m²)
  • Acute renal insufficiency due to hepato-renal syndrome
  • Perioperative liver transplantation period 1

• NSF is characterized by severe and progressive skin induration and can affect multiple organs 1

• The risk of NSF in patients with mild to moderate renal insufficiency or normal renal function is unknown but appears to be extremely low 1

Advantages of MRA vs Other Angiographic Methods

When comparing MRA to other angiographic techniques:

• Gadolinium-enhanced MRA provides excellent characterization of renal arteries with less nephrotoxicity than iodinated contrast used in CT angiography 1

• Traditional catheter-based contrast angiography carries higher risks of contrast-induced acute renal failure:

  • <3% in patients with neither diabetes nor chronic kidney disease
  • 5-10% in patients with diabetes
  • 10-20% in those with chronic kidney disease
  • 20-50% in those with both diabetes and chronic kidney disease 1

Clinical Decision Algorithm for MRA in Renal Impairment

1. For patients with normal renal function:

   • Contrast-enhanced MRA is safe and preferred 1
   • Risk of serious allergic reactions to gadolinium is very low (<0.01%) 1

2. For patients with mild to moderate renal impairment:

   • Consider risk-benefit ratio carefully
   • Use lowest possible dose of gadolinium that provides diagnostic images 1
   • Consider group II contrast agents which may have better safety profiles 1

3. For patients with severe renal impairment (GFR <30 mL/min/1.73 m²):

   • Avoid gadolinium-based contrast agents if possible 1
   • Consider alternative imaging methods:
     • Unenhanced MRA techniques (sensitivity 74%, specificity 93%) 1
     • Ultrasound (first-line screening) 1
     • Ferumoxytol-enhanced MRA (non-gadolinium alternative) 2
   • If gadolinium must be used, consider prompt dialysis afterward 1

Important Caveats and Pitfalls

1. Overestimation of stenosis: MRA tends to overestimate the degree of renal artery stenosis, potentially leading to false-positive diagnoses 3

2. Stent evaluation limitations: MRA is less useful in patients with metallic renal artery stents due to inability to image inside the stent to detect restenosis 1

3. NSF risk factors: The risk of NSF appears to be related to:

   • Severity of renal impairment
   • Stability of the gadolinium chelate used
   • Dose of contrast administered 4

4. Balancing risks: When considering MRA in patients with renal impairment, always weigh the diagnostic benefits against the potential risks, and consider whether alternative imaging methods would be sufficient 1, 4

By following these guidelines, MRA can be safely used in most patients, with appropriate precautions for those with significant renal impairment.