What is the difference between CT angiography, MR angiography, and cerebral angiography?
How CT angiography, MR angiography, and cerebral angiography differ: how they are performed, the contrast materials they use, their advantages and limitations, and what to tell your care team.
By Dr. Martin Roberto Casas MartínezOct 3, 20266 min read
In this article
Summary: CT angiography uses X-rays and iodine contrast injected through a vein; MR angiography uses a magnet and radio waves, without radiation, with or without contrast; cerebral angiography guides a catheter through an artery to the neck and injects contrast directly into the blood vessels of the brain. They are not always interchangeable: each answers different questions, and the specialist chooses based on the case.
When an aneurysm, malformation, or narrowing of an artery is being evaluated, the care team commonly requests images of the blood vessels in the brain. Understanding the differences between CT angiography, MR angiography, and cerebral angiography can help you prepare, share important information, and follow the discussion about your treatment.
All three tests aim to visualize blood vessels, but they use different technologies and have different risks.
What does each test do?
CT angiography combines a CT scan with contrast injected into a vein; MR angiography produces images using a powerful magnet and radio waves; cerebral angiography injects contrast directly into the arteries through a catheter guided by X-rays.
- •CT angiography (CTA): the X-ray machine rotates around you, and a computer creates slices that can be combined into three-dimensional models. The scan usually takes a few minutes or less.
- •MR angiography (MRA): it is performed inside a tunnel-shaped scanner; it may take an hour or longer, and the machine makes loud noises.
- •Cerebral angiography with a catheter: a catheter (a thin, hollow tube) is inserted through the groin or wrist and advanced to the arteries in the neck. It shows how blood flows through the blood vessels in the brain.
What contrast material does each test use, and what should I tell my care team?
CT angiography and catheter angiography use iodine-based contrast; MR angiography, when needed, uses gadolinium. Before the test, tell your care team if you have kidney problems, an allergy to contrast material, diabetes, or metal implants.
Contrast material is a substance that makes blood vessels easier to see. Iodine can worsen kidney function in people whose kidneys are already impaired and can cause allergic reactions; if you take metformin, your care team may recommend precautions. Gadolinium rarely causes allergies, but it can be harmful for people with kidney disease who are on dialysis. For MR angiography, also let the team know if you have aneurysm clips, stents, a pacemaker, or other devices.
What are the advantages and limitations of each?
None is better in every case. CT angiography is quick but uses radiation; MR angiography avoids radiation but takes longer and may be affected by implants; catheter angiography provides highly detailed images and can be used for treatment, but it is invasive.
General comparison of the three tests
- •CT angiography — Advantages: Quick; no arterial catheter required. Limitations: Radiation; iodine contrast
- •MR angiography — Advantages: No radiation; can be performed without contrast. Limitations: Takes longer; noisy; restrictions related to metal implants
- •Catheter angiography — Advantages: Highly detailed images; can be combined with treatment. Limitations: Invasive; risks related to arterial access
Risks of angiography include bleeding or a blood clot at the entry site and, in rare cases, damage to an artery that can cause a stroke.
Why might more than one test be requested?
Because they are not always interchangeable: one test may detect a finding, while another clarifies it. After a CT or MRI, angiography is sometimes recommended to obtain more detailed information or prepare for treatment.
MedlinePlus notes that catheter angiography is used less often today because CT angiography and MR angiography provide good images without the need for a catheter. Even so, it may be part of treatment for an aneurysm or a stroke, since the same access can be used to diagnose and treat in a single procedure. Being asked to have another test does not, by itself, mean that the problem is more serious.
Who decides which test I need?
The specialist recommends a test based on the question that needs to be answered, the urgency, your kidney function, your implants, and your previous tests; you can take part by sharing your questions and medical history.
That is why you should not request a test on your own or compare your case with someone else’s. If you have sudden symptoms, such as a very severe headache, weakness on one side of the body, or difficulty speaking, call 911: in the emergency department, the team will decide which test to perform and when.
Frequently asked questions
Does cerebral angiography hurt?
You usually feel a pinch from the local anesthetic and brief pressure as the catheter advances; the contrast may make your face feel warm for a few seconds. Afterward, you must keep your leg or wrist still for the recommended amount of time.
Can I have MR angiography if I have clips or a stent?
It depends on the device. Tell the team about aneurysm clips, stents, pacemakers, and other implants beforehand, because the magnet could affect how they work or move them. The team will decide whether the test is safe or whether another option is preferable.
Is the radiation from CT angiography dangerous?
The risk from a single test is low, although having many CT scans over time can increase it. You and your doctor should weigh that risk against the benefit of getting an accurate diagnosis.
What should I ask before the test?
If sudden neurological symptoms occur, call 911 first. For a scheduled test, bring a list of your medications and implants, and ask:
- •What question is this test intended to answer, and why this test rather than another?
- •Will I need contrast, and what should I tell my care team about kidney problems, allergies, diabetes, or medical devices?
- •If the results are inconclusive, what test would come next, and who will explain the results to me?
For non-urgent questions or to request an individual assessment, you can contact the office.
Informational notice: This content is for informational purposes and does not replace a medical consultation or constitute a diagnosis.
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