Frequently Asked Questions

15. What is an MRI?

Another imaging technique used for stroke patients is the magnetic resonance imaging or MRI scan. MRI uses magnetic fields to detect a variety of changes in the brain and blood vessels caused by a stroke.

One effect of ischemic stroke is the slowing of water movement through the injured brain tissue. An MRI can show this type of damage very soon after the stroke symptoms start.

MRI and CT are equally accurate for determining when hemorrhage is present. The benefit of MRI over a CT scan is more accurate and earlier diagnosis of ischemic stroke especially for smaller strokes and transient ischemic attacks (TIAs). Also, MRI can be more sensitive than CT for detecting other types of neurologic disorders that mimic the symptoms of stroke. However, MRI cannot be performed in patients with certain types of metallic or electronic implants, such as pacemakers for the heart.

Although increasingly used in the emergency diagnosis of stroke, MRI is not immediately available at all hours in most hospitals, where CT is used for acute stroke diagnosis. Also, MRI typically takes longer to perform than CT, and therefore may not be the first choice when minutes count.