MR Angiography

Neuroradiologists may perform MRA and MRI together as complementary examinations to obtain a more complete view of the blood vessels.

MRA is particularly valuable in screening for atherosclerosis, or hardening of the arteries. Over time, fat can be deposited along the walls of medium and large arteries in the body, causing them to become narrowed or even blocked. This blockage can eventually lead to a transient ischemic attack or even a stroke.

Neuroradiologists also perform MRA to detect a brain aneurysm, which is an abnormal widening or ballooning of a cerebral vessel. Brain aneurysms occur when an injury or congenital defect weakens the wall of the vessel. Aneurysms are particularly dangerous because they can burst and cause potentially fatal bleeding.

In addition, MRA is helpful in assessing vascular malformations, which occur when blood or lymph vessels fail to develop normally before birth. The affected vessels become tangled and change the normal flow of the blood through the brain. Some patients have headaches and seizures, but others may be asymptomatic. Vascular malformations can cause hemorrhage and subsequent neurologic damage. Lastly, MRA may aid in evaluating some types of headaches.

In addition, because MRA relies on the natural magnetic properties of hydrogen atoms in the body, injections of contrast material are not always needed. This feature is especially important in patients who have had allergic reactions to contrast agents in the past.

One drawback of MRA is that it does not depict small vessels or extremely slow blood flow as well as conventional angiography does. However, with its advantages, MRA is a good examination for many patients.

You lay down on a table that slides into the tubelike opening in the MRI unit. Before performing the actual imaging part of the examination, the physician and technologist go to an adjoining room where they can observe and speak with you at all times. When imaging occurs, the machine may produce a tapping noise, but you can wear earplugs to block this out. You lay still for a few seconds at a time while the images are being generated.

The MRA procedure can be performed on an outpatient basis. The neuroradiologist reviews the angiograms, and the results are usually available a few hours later.

The image on the left shows a blockage (arrow) in a segment of the right internal carotid artery.

The image on the right is another type of magnetic resonance angiogram. This image shows different vessels in the brain from another point of view.

For most people, the only discomfort is from the needle puncture during intravenous administration of contrast agent. A few patients, perhaps 1 in 1,000, might have an allergic reaction to contrast material.

MRA can be performed in most patients. People with claustrophobia may find it difficult to remain inside the small confines of the imaging unit. For these patients, the use of sedatives or new machines with an open design may be helpful.

MRA is usually not performed in pregnant women, unless they have a medical emergency.

MRA cannot be performed in some patients because they have metallic implants. Devices such as hearing aids and cardiac pacemakers or defibrillators and objects such as orthopedic pins and screws, aneurysm clips, shrapnel, and jewelry can interfere with the magnetic field. Conversely, the magnetic forces created by the imaging machine can cause the devices to malfunction or the objects to move inside the patient's body.