MR Angiography (MRA)
Imaging blood vessels without ionising radiation — and increasingly without any contrast injection at all.
The main techniques
- Time-of-flight (TOF): non-contrast; bright flowing blood against saturated static tissue. Workhorse for the circle of Willis and carotids.
- Phase-contrast (PC): encodes velocity — gives flow direction and quantification as well as anatomy.
- Contrast-enhanced (CE-MRA): gadolinium-timed acquisition; fast, large-coverage, high-quality for aorta and peripheral runoff.
- Newer non-contrast: e.g. quiescent-interval and balanced-SSFP methods for renal, peripheral and thoracic vessels.
Non-contrast MRA is especially valuable where gadolinium is best avoided — impaired renal function or repeated follow-up.
Common uses
- Neurovascular: intracranial aneurysms, stenosis, dissection; carotid stenosis.
- Aorta: aneurysm surveillance, dissection follow-up, coarctation.
- Renal: renal artery stenosis.
- Peripheral: runoff assessment in claudication/critical limb ischaemia.
Trade-offs
MRA avoids radiation and iodinated contrast but is slower and more motion-sensitive than CT angiography, and can overestimate stenosis (especially TOF). CTA is often preferred acutely for speed. Technique is matched to the vascular territory and the clinical question.
Reference: Hartung MP et al. Magnetic resonance angiography: current status and future directions. J Cardiovasc Magn Reson 2011;13:19.
Educational summary for clinicians; technique choice follows local protocols. Not medical advice.