What is an MRA (Magnetic Resonance Angiography)?

Magnetic Resonance Angiography (MRA): Definition and Applications

Magnetic Resonance Angiography (MRA) is a specialized non-invasive imaging technique that uses magnetic resonance technology to visualize blood vessels and blood flow without radiation exposure or invasive catheterization. 1

Technical Principles of MRA

MRA works through several key mechanisms:

• Hardware Components:

  • Superconducting magnet (typically 1.5T or 3.0T)
  • Gradient coils that create spatial variations in the magnetic field
  • Radiofrequency coils that transmit and receive signals
  • Receiver coils that measure MR signals at resonance frequency 1

• Acquisition Techniques:

  • Non-contrast techniques:

    • Time-of-flight (TOF): Uses blood flow effects on signal; provides strong blood signal without contrast but has longer acquisition times 1
    • Phase-contrast (PC): Measures differences in phases between stationary and moving spins; allows quantitative flow velocity measurements and flow direction discrimination 1

  • Contrast-enhanced techniques:

    • CE-MRA: Uses gadolinium-based contrast agents that shorten T1 relaxation time of blood, creating bright signal intensity in T1-weighted images 1
    • Time-resolved MRA: Enables dynamic visualization of contrast transit through vasculature 1

Clinical Applications

MRA has numerous applications across different vascular territories:

1. Neurological Applications:

   • Detection of intracranial aneurysms (≥3mm) 1
   • Evaluation of arterial stenosis and occlusions 2
   • Diagnosis of arterial dissections 2
   • Assessment of cerebrovascular malformations 2
   • Monitoring of dural venous thrombosis 3

2. Cardiovascular Applications:

   • Coronary artery evaluation with less invasiveness than catheter angiography 1
   • Assessment of congenital heart disease 1
   • Evaluation of cardiac function, structure, blood flow, and viability 1
   • Quantification of blood flow and pressure gradients 1

3. Peripheral Vascular Applications:

   • Evaluation of peripheral arterial disease 4
   • Assessment of venous thrombosis 3

Advantages of MRA

• Non-invasive technique with no exposure to ionizing radiation 1
• No need for iodinated contrast media in non-contrast techniques 1
• Can be combined with other MR techniques for comprehensive assessment 1
• Excellent for follow-up imaging, especially in pediatric patients 1
• Can visualize all arterial feeders and collaterals simultaneously 1
• Can distinguish between mural and luminal thrombosis 1
• Outpatient procedure with fewer restrictions than conventional angiography 5

Limitations and Considerations

• May give false-negative results in vessels with low or turbulent flow 1
• Resolution generally poorer than conventional angiography 5
• May require sedation in patients with claustrophobia 1
• Time-of-flight techniques have longer acquisition times 1
• Potential artifacts from metallic implants (stents, clips) 1
• Contraindicated in patients with certain implanted devices 5

Follow-up Protocols

For specific conditions like intracranial aneurysms, follow-up protocols have been established:

• For untreated intracranial aneurysms: MRA every 5 years for life 1
• For endovascularly treated aneurysms: MRA at 1,2, and 5 years 1
• For complex aneurysms: More frequent monitoring may be required 1

MRA has evolved from a research tool to an essential clinical examination that is increasingly becoming the screening modality of choice for many vascular diseases 6, offering comprehensive anatomic and physiologic information without the risks associated with conventional angiography.