MRA Recognition Pattern

Systematic approach to interpreting MR angiography with vascular territories, pathological patterns, and protocol optimization

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1. MRA Protocols

A. Standard Techniques

• • Time-of-Flight (TOF):
  - Flow-related enhancement
  - Best for high-flow vessels (Circle of Willis)
  - 3D acquisition (0.5-0.7mm slices)
• • Contrast-enhanced (CE-MRA):
  - Bolus timing critical
  - 1.5-2mm isotropic resolution
  - Multiphasic acquisition (arterial/venous)
• • Phase-contrast:
  - Flow quantification
  - VENC settings: 40-100 cm/s (venous), 80-150 cm/s (arterial)

B. Anatomical-specific Protocols

• • Head/Neck:
  - Cover from aortic arch to vertex
  - ECIC anastomosis evaluation
• • Runoff:
  - Bolus chase technique
  - Three-station (aorta to feet)

2. Vascular Territories

A. Cerebral Circulation

Artery

Territory

Key Branches

ACA

Medial frontal/parietal

Pericallosal, callosomarginal

MCA

Lateral hemispheres

M1-M4 segments

PCA

Occipital lobes

P1-P4 segments

B. Aortic Branches

• • Great vessels:
  - Brachiocephalic
  - Left CCA
  - Left subclavian

3. Stenosis Assessment

A. NASCET Criteria

Grade

Stenosis %

Hemodynamic Effect

Mild

<50%

None

Moderate

50-69%

Distal flow reduction

Severe

70-99%

Collateral flow

B. Pitfalls

• • Overestimation:
  - Turbulent flow
  - Vessel tortuosity

4. Aneurysm Detection

A. Key Locations

• • Anterior circulation:
  - ACOM (40%)
  - MCA bifurcation (20%)
• • Posterior circulation:
  - PCOM (25%)
  - Basilar tip (10%)

B. Rupture Risk Factors

• • Morphology:
  - Size >7mm
  - Irregular shape
  - Daughter sac

5. Vascular Dissection

A. Imaging Signs

Feature

Appearance

Intimal flap

Linear filling defect

Double lumen

True + false lumen

Wall hematoma

T1 hyperintense crescent

6. Reporting Template

• 1. Technique: Type (TOF/CE), coverage
• 2. Vessel patency:
  - Stenosis grade/location
  - Collateral circulation
• 3. Aneurysms:
  - Size/location/morphology
  - Branch involvement
• 4. Dissections:
  - Extent
  - Branch vessel compromise
• 5. Incidental findings

Always correlate with non-contrast MRI when available. For TOF MRA, recognize flow-related artifacts at vessel bends. In CE-MRA, verify proper arterial phase timing. Document variant anatomy (fetal PCA, vertebral dominance) as it affects intervention planning. For follow-up aneurysms, measure consistently (outer wall to outer wall). Include relevant measurements (stenosis length, aneurysm dimensions) for treatment planning.

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