Magnetic Resonance Angiography (MRA) is an imaging technique used to visualize blood vessels. This noninvasive method is particularly useful for examining the carotid arteries, the vessels in the neck that supply blood to the brain. An MRA provides detailed images of these arteries, allowing for an assessment of their structure and function.
The Carotid Arteries Explained
The carotid arteries supply oxygenated blood to the brain, head, and neck. Originating in the chest, the right common carotid artery stems from the brachiocephalic artery, while the left common carotid artery arises directly from the aorta, the body’s main artery. These two arteries travel upward through the neck, one on each side. Their pulse can be felt by gently pressing a finger on the side of the neck.
Each common carotid artery divides into two branches at a point called the carotid bifurcation. The external carotid artery supplies blood to the face, scalp, and neck. The internal carotid artery provides blood to the front part of the brain, which controls functions like thought, personality, speech, and sensory and motor activities. The health of these arteries is directly linked to proper brain function.
Magnetic Resonance Angiography for Carotids
For a carotid MRA, a patient lies inside a large, cylindrical magnet. The machine uses a powerful magnetic field and radio waves to generate signals from flowing blood in the carotid arteries. These signals are then converted by a computer into detailed, cross-sectional images. Unlike X-ray angiography, MRA does not use ionizing radiation.
To enhance visibility, a gadolinium-based contrast agent may be administered intravenously. This substance makes the blood flow appear brighter on the scan, creating a clearer image of the arteries. This technique, known as contrast-enhanced MRA (CE-MRA), is effective for visualizing the arteries’ length and shape. The choice between a contrast or non-contrast MRA depends on the information the physician needs.
Why a Carotid MRA is Performed
A physician may order a carotid MRA due to symptoms suggesting an issue with blood flow to the brain. A common reason is to investigate the cause of a transient ischemic attack (TIA), or “mini-stroke,” and other strokes. These events can be caused by a blockage or narrowing in a carotid artery, which an MRA can identify.
The procedure is also used to diagnose and monitor carotid artery stenosis, a condition where plaque, a substance made of fat, cholesterol, and calcium, builds up inside the arteries, causing them to narrow. This narrowing can restrict blood flow and increase the risk of stroke. An MRA can also detect other abnormalities such as an aneurysm, a bulge in the artery wall, or a dissection, a tear in the artery lining. It may also be performed as a follow-up to other imaging tests or to plan for surgical intervention.
What a Carotid MRA Reveals
A radiologist examines the MRA results for the characteristics of healthy arteries. Normal carotid arteries appear as smooth, open tubes with uniform width. The images should show a clear path with distinct internal and external branches.
The MRA can reveal several types of abnormalities. The most frequent finding is carotid artery stenosis, and the images can precisely locate the plaque buildup and measure the degree of narrowing. This measurement helps determine the severity of the condition. The scan can also identify complete blockages, or occlusions, where the artery is entirely closed off.
Other findings include aneurysms, which appear as localized, balloon-like bulges in the artery wall. A carotid artery dissection can be visualized as a tear in the inner layer of the artery, which can disrupt blood flow. This detailed map of the carotid arteries helps guide diagnosis and treatment decisions.