Which provides a better view of dissection, Magnetic Resonance Angiography (MRA) or Computed Tomography Angiography (CTA)?

CTA Provides Superior Visualization of Arterial Dissection in Most Clinical Scenarios

For acute dissection evaluation, CTA is the preferred imaging modality due to its superior spatial resolution, rapid acquisition time, and widespread availability, achieving 98-100% sensitivity and specificity for detecting dissection. 1

Primary Recommendation: CTA as First-Line Imaging

CTA should be your primary imaging choice for dissection evaluation because it offers several critical advantages:

• Superior spatial resolution compared to MRA, allowing better visualization of the intimal flap, entry tears, and branch vessel involvement 1
• Faster scan times (entire aorta imaged within seconds), reducing motion artifact and making it ideal for unstable patients 1, 2
• Immediate availability in emergency settings, whereas MRA is often not available on an emergency basis 3
• Better tolerance of metal artifacts from prior surgical hardware or implanted devices 1
• Excellent visualization of calcification, which helps identify displaced intimal calcifications—a key diagnostic feature 4

When MRA May Be Preferable

MRA has specific advantages in select scenarios:

• Detection of intramural hematoma: MRA's superior soft-tissue contrast makes it better than CTA or conventional arteriography for identifying intramural hematoma, showing high signal intensity from methemoglobin formation 1, 3
• Heavily calcified vessels: MRA does not suffer from calcium-related artifacts that can overestimate stenosis on CTA 1
• Follow-up imaging: For serial surveillance where radiation exposure is a concern, particularly in younger patients 2
• Contraindication to iodinated contrast: When patients have severe renal dysfunction or contrast allergies 3

Diagnostic Performance Comparison

CTA Performance

• Sensitivity: 98-100% for aortic dissection 1
• Specificity: 98-100% 1
• Intimal flap visible approximately 70% of the time 1
• Considered the diagnostic reference standard for aortic imaging 1

MRA Performance

• Sensitivity: 90-100% for aortic dissection 3
• Specificity: 100% 3
• Can quantify flow in true and false lumens using phase contrast sequences 3
• Demonstrates 100% sensitivity for thrombus formation and pericardial effusion 3

Specific Anatomic Considerations

Cervical Dissection

For cervical arterial dissection (carotid/vertebral):

• CTA is slightly preferable to MRA for identification of blunt cervical arterial injuries 1
• CTA sensitivity: 41-98%, specificity: 81-100% 1
• MRA sensitivity: 75%, specificity: 67% 1
• However, MRA may be superior for detecting intramural hematoma in cervical vessels using T1-weighted fat-suppressed sequences 1

Thoracic and Abdominal Dissection

• CTA is the standard for acute aortic syndromes 2, 5
• Multiphase dynamic CTA protocols can reveal additional diagnostic information including membrane oscillation and dynamic flow patterns 6
• MRA clearly demonstrates the extent of dissection and depicts the distal ascending aorta and aortic arch in more detail than echocardiography 3

Critical Limitations to Avoid

CTA Pitfalls

• Calcium artifact: Can overestimate stenosis severity in heavily calcified arteries; consider dual-energy CTA to reduce beam-hardening artifact 1
• Contrast-induced nephropathy risk: Optimize protocols to minimize contrast dose 2
• Radiation exposure: Particularly concerning for follow-up imaging 2

MRA Pitfalls

• Limited emergency availability: Often not feasible for unstable patients 3
• Longer acquisition times: Increases motion artifact risk 1
• "Blind spot" in distal ascending aorta and anterior aortic arch due to trachea/bronchus interposition 3
• Cannot visualize calcification: May miss displaced intimal calcifications 4

Practical Clinical Algorithm

1. Acute/unstable patient with suspected dissection: Use CTA (faster, more available) 1, 2
2. Stable patient with renal dysfunction or contrast allergy: Use non-contrast MRA with ECG-gating 3
3. Suspected intramural hematoma: Consider MRA for superior soft-tissue characterization 1, 3
4. Heavily calcified vessels: MRA avoids calcium artifact 1
5. Follow-up surveillance: MRA preferred to avoid cumulative radiation 2
6. Cervical dissection: CTA first-line, but add MRA if intramural hematoma suspected 1