MR angiography, almost always shortened to MRA, is the way you get a detailed map of someone's arteries or veins without X-rays, without an arterial puncture, and, quite often, without any injected contrast at all. It is the workhorse test when the clinical question is about blood vessels but the patient cannot, or should not, have a CT angiogram.
This is a plain-English guide to what MRA actually is, how it differs from CT angiography, the five clinical questions it answers best, its real limitations, and what it costs privately in the UK in 2026.
One-line answer
MR angiography is an MRI scan tuned specifically to image the inside of blood vessels, either using clever motion-sensitive sequences that need no injection at all, or using gadolinium contrast injected through a small arm cannula, producing high-resolution 3D images of arteries and veins without any ionising radiation.
The techniques: TOF (no contrast) vs contrast-enhanced MRA
There are two families of MRA sequence, and the choice matters for you as a patient because one involves an injection and the other does not.
Time-of-flight MRA, always abbreviated TOF, exploits the fact that blood flowing into an imaging slice is 'bright' relative to the stationary tissue around it. No contrast is injected. TOF is excellent for intracranial arteries and the carotid bifurcation in the neck, and it is the default for suspected berry aneurysm and for carotid stenosis screening. Its weakness is slow or turbulent flow, which it can artefactually make look narrowed.
Contrast-enhanced MRA, CE-MRA, uses a small injection of gadolinium contrast into an arm vein. The scanner then acquires images during the brief window when the contrast is filling the artery of interest. This gives a much cleaner, sharper picture of larger and more distant vessels, and it is the standard for the aorta, the renal arteries and the peripheral arteries of the legs. The dose of gadolinium is small and, in modern UK practice, uses macrocyclic agents with an excellent safety profile.
A well-designed MRA protocol often uses both. TOF for the intracranial circle of Willis, CE-MRA for the neck vessels below, all in one visit.
When MRA beats CTA
CT angiography is faster, more widely available, and slightly better at showing calcified plaque. For a lot of vascular questions it is the right first test. But there are five situations in which MRA is not just an alternative to CTA, it is actively the better test:
- The patient cannot have iodinated contrast. Iodine allergy is the classic contraindication. Even without a documented allergy, a history of severe reactions to previous contrast studies pushes the choice toward MRA.
- Reduced kidney function. Iodinated CT contrast carries a real risk of contrast-induced nephropathy in patients with an eGFR below about 30 to 45. Gadolinium contrast, in the doses used for MRA, does not carry the same acute nephrotoxicity risk. MRA is the safer choice.
- Pregnancy. Ionising radiation to a pregnant patient is avoided wherever possible, particularly for imaging the abdomen and pelvis. MRA is radiation-free.
- Documented allergies or previous reactions. Even mild previous iodine reactions are enough for many radiologists to switch to MRA if the clinical question can be answered that way.
- Deliberate radiation avoidance. Young patients being followed up over years for a known aneurysm or vascular anomaly benefit enormously from cumulative-dose avoidance. MRA replaces repeated CTA over a lifetime of follow-up.
The five clinical questions MRA answers
MRA is not a general 'let's have a look' scan. It is requested to answer specific vascular questions. These are the five most common in UK practice in 2026.
1. Intracranial aneurysm. A time-of-flight MRA of the circle of Willis is the standard way to screen for, and follow up, cerebral aneurysms in patients with a family history, with a small known aneurysm being watched, or after a subarachnoid haemorrhage. It picks up aneurysms of 3 mm and larger reliably.
2. Carotid artery stenosis. Narrowing of the carotid artery in the neck is a leading cause of stroke. Contrast-enhanced MRA of the carotid arteries grades the stenosis and helps the vascular surgeon decide between medical therapy, carotid endarterectomy or stenting.
3. Renal artery stenosis. Narrowing of the renal artery is a treatable cause of resistant hypertension. Contrast-enhanced MRA of the renal arteries is the go-to test where iodinated CTA is contraindicated, which is often the case because these patients frequently have impaired kidney function.
4. Peripheral arterial disease. When patients present with claudication - leg pain on walking - or a poor ankle-brachial index, contrast-enhanced MRA of the lower limbs maps the arterial tree from the aorta to the ankles. It guides angioplasty or bypass decisions.
5. Aortic dissection follow-up. After the acute event has been treated, most typically initially imaged with CTA, patients need lifelong surveillance of the residual dissection or graft. MRA is often preferred for this because it avoids the cumulative radiation of repeated CTAs over decades of follow-up.
MR venography for suspected venous sinus thrombosis
MRA has a close cousin, MR venography or MRV, which images veins rather than arteries. Its most important use is imaging the dural venous sinuses of the brain when a clinician suspects cerebral venous sinus thrombosis, a clot in one of the large veins draining the brain. It is a diagnosis that is easy to miss on a routine brain MRI and CT, and MRV is the definitive test.
MRV is usually requested alongside a standard brain MRI in patients with new-onset severe headache, unexplained raised intracranial pressure on fundoscopy, or a first seizure in an adult with no prior history, particularly in women of reproductive age, in pregnancy, or in the postpartum period.
