Magnetic resonance imaging (or MRI) is a test the provides very accurate pictures of the brains and arteries. MRIs are useful for detecting a wide array of blood vessel and brain abnormalities, and is the most accurate technique to determine which areas of the brain have been irreversibly damaged by ischemic stroke. In addition to stroke, MRIs can be used to diagnose several other abnormalities, such as tumors, blood clots, infections and even disorders like multiple sclerosis.

In comparison with CT scans, MRIs are often more accurate, demonstrating brain abnormalities that are too small or precisely located for a CT scan to detect. Another distinction (and benefit) of MRI is that unlike a CT scan, an MRI can be performed without X-rays or iodinated contrast. But the MRI scan takes longer, and caution must be taken if the patient has metal medical devices (pacemakers, etc.) or other metal in the body, because it can either cause poor images or pose a danger to the patient in the magnetic field.

How MRIs work

During an MRI, the patient lies on a table that moves into the opening of the MRI machine. This machine creates a magnetic field, which serves to briefly alter polarity of the water molecules in the patient’s body. The response to this magnetic field is then detected and used to create a highly accurate and detailed image of the patient’s brain. The test usually takes between 30 to 90 minutes and is completely painless with no known side effects.

One common difficulty some patients face during an MRI is the need to lie flat, without moving, in a relatively confined space for up to an hour. If you’re claustrophobic or otherwise believe this might be a problem for you, you should discuss this with your care team.

Types of MRI

There are several types of MRI scans, known as image sequences. Each sequence highlights different aspects of brain tissue, so it can be used to answer different questions. A diffusion-weighted MRI, for instance, can be useful for detecting abnormalities in the first few hours after ischemic stroke. An MRI can also be used to obtain an image of the blood vessels that supply the brain, which is known as a magnetic resonance angiography (or MRA).