Which imaging modality, Magnetic Resonance Angiography (MRA) or Computed Tomography Angiography (CTA), has less radiation exposure?

MRA Has No Radiation Exposure While CTA Involves Significant Radiation

Magnetic Resonance Angiography (MRA) has zero radiation exposure, making it the preferred imaging modality over Computed Tomography Angiography (CTA) when radiation exposure is the primary concern. 1

Radiation Exposure Comparison

MRA

• No ionizing radiation - MRA uses magnetic fields and radio waves to generate images
• Completely radiation-free imaging technique
• Particularly beneficial for:
  • Young patients 2
  • Patients requiring serial/repeated imaging 1
  • Pediatric patients who are more sensitive to radiation effects 1

CTA

• Uses ionizing radiation (X-rays)
• Radiation exposure varies by protocol but is significant
• Radiation effects are cumulative with repeated exposures 1
• Radiation confers a significant risk of carcinogenesis, especially in children 1

Clinical Applications and Selection Factors

When MRA is Preferred

• Screening for cerebral aneurysms 3
• Surveillance of untreated aneurysms 1, 3
• Anomalous coronary artery evaluation (Class IIa, level of evidence B) 1
• Young patients requiring vascular imaging 2
• Patients with renal impairment (gadolinium is less nephrotoxic than iodinated contrast) 2
• Long-term follow-up imaging 1

When CTA May Be Preferred

• Following clipped aneurysms (due to metal artifact on MRA) 1
• Acute conditions requiring rapid imaging (shorter acquisition time) 2
• Patients with contraindications to MRI (pacemakers, certain implants)
• When higher spatial resolution is needed for smaller vessels 1

Additional Considerations

Contrast Agents

• MRA: Uses gadolinium-based contrast (when contrast-enhanced)
  • Contraindicated in severe renal dysfunction (eGFR <30 mL/min/1.73m²) 3
  • Non-contrast MRA techniques are available 3
• CTA: Uses iodinated contrast
  • Higher risk of nephrotoxicity 2
  • Higher risk of adverse reactions 4

Image Quality Factors

• MRA:
  • Excellent for soft tissue characterization
  • Can assess vascular injury and intramural hematoma 1
  • May have longer acquisition times 2
• CTA:
  • Higher sensitivity for smaller aneurysms 1
  • Faster acquisition time 1
  • Better for evaluating calcification

Clinical Decision Algorithm

1. If radiation exposure is the primary concern: Choose MRA
2. If patient has renal impairment:
   • Mild to moderate: Consider non-contrast MRA
   • Severe: Individualize based on risk-benefit (limited contrast CTA may be considered)
3. If patient has MRI contraindications: Use CTA with dose-reduction techniques
4. If following up treated aneurysms:
   • Clipped aneurysms: CTA preferred
   • Coiled aneurysms: MRA preferred

Pitfalls to Avoid

• Using CTA for routine surveillance in young patients without considering radiation risks
• Performing contrast-enhanced MRA in patients with severe renal dysfunction
• Overlooking non-contrast MRA options when contrast is contraindicated
• Failing to consider the cumulative radiation dose in patients requiring serial imaging

The American College of Radiology and American Heart Association both acknowledge radiation concerns with CTA and recommend MRA when radiation exposure is a significant consideration, particularly for pediatric patients and those requiring long-term follow-up imaging 1.