Signs of stroke can show up on an MRI for years after the initial event. However, if the symptoms were mild, a person may not know they had a stroke until long afterward.

A stroke happens when blood cannot get to parts of the brain, as a result of either a blockage or a bleed. This leads to a lack of oxygen and nutrients, which causes cells in the brain to die.

A doctor may be able to see signs of a stroke within minutes or hours of a person’s first symptoms. Medical imaging can also determine the type of stroke a person has had and show which areas of the brain it affected.

Read on to learn more about how long strokes show up on MRI and CT scans.

A doctor analyzing an MRI scan for stroke on a screen.Share on Pinterest
Andrew Brookes/Getty Images

Depending on the type of machine, an MRI can potentially detect new strokes within minutes. An MRI can also detect old strokes for decades after they happen.

The fastest type of MRI is diffusion-weighted imaging (DWI). It measures shifts in fluid in the brain and can detect a stroke soon after its onset.

An MRI can also detect evidence of past strokes. For example, in an older 2014 study, researchers used MRI scans to monitor changes in the brain between 3 months and 20 years after a stroke.

The way a stroke looks on an MRI depends on the type of MRI machine and how long it has been since the onset of the stroke.

Very early imaging with a DWI MRI will show changes in the fluid balance in the brain. Other potential signs of a stroke include swelling, active bleeding, and a blood clot.

An old stroke will look different on medical imaging scans than a recent stroke, consisting of small white spots that indicate damaged tissue. This happens because the brain continues to change in the hours, days, weeks, and years after a stroke.

An MRI can also show areas where brain tissue has shrunk. This happens when brain cells die from a lack of blood flow.

An MRI provides a very detailed image of the brain. Doctors consider MRI more accurate than a CT scan for finding out exactly which parts of the brain a stroke affected.

Another MRI several days after the stroke can provide more details about the type of stroke a person had and the damage to the brain.

Yes, MRI scans can detect silent strokes.

Sometimes, a person may not know they have had a stroke or a transient ischemic attack, which doctors may also call a ministroke. The symptoms may have been mild, or the person may have mistaken the symptoms for something else. This is known as silent stroke, and it affects 8 to 11 million people in the United States every year.

A person may have an MRI scan later in life for another reason and find out that they had a stroke in the past.

Evidence of a stroke can be visible on an MRI even decades later. The brain changes and does not look the way it did before a stroke.

An MRI may be able to show when a person is at risk for a stroke, although it cannot predict it with certainty.

Doctors can use MRI scans to check the health of blood vessels in the brain. If a person has risk factors for stroke, doctors may order a high resolution MRI scan to look for areas in the brain where vessels are narrow and blood flow is restricted.

An MRI may also show areas where plaque is unstable. Plaque is a substance that can build up inside the blood vessels, causing restrictions or blockages.

If a piece of plaque breaks off, it may block blood flow to parts of the brain and cause a stroke. Doctors can use this information to begin treatments and try to prevent this from happening.

A CT scan is another type of medical imaging test that doctors can use to diagnose stroke. CT scanners tend to be more widely available in hospitals than MRI machines, and a CT scan takes less time than an MRI.

Because of this, many doctors still consider CT scans their first choice for urgent imaging. A CT scan does not provide as much detail as an MRI, but it gives doctors enough information to move forward.

After someone has a stroke, the priority is to diagnose the type of stroke so the person can receive the right treatment. Both CT or MRI scans can identify the stroke type, but CT scans cannot always find the location of a blood clot. However, they can rule out a hemorrhagic stroke and other potential causes for the person’s symptoms.

Some research supports using an MRI first, rather than a CT scan. For example, a 2019 study suggests that finding out more information about the size and location of the blood clot in ischemic stroke is worth the extra minutes an MRI takes.

Can a CT scan detect old strokes?

Yes – like an MRI, a CT scan can detect old strokes. There may be changes in the volume of brain cells where the stroke took place. On a CT, this looks like white spots.

Will a stroke always show up on a CT?

A CT scan is excellent for ruling out a hemorrhagic stroke or other causes for a person’s symptoms, such as a tumor. However, a CT scan does not provide the same level of detail as an MRI.

For example, a doctor cannot always see the site of an ischemic stroke on a CT scan. Also, in the first 6 hours after a stroke, it can be hard to confirm an ischemic stroke via CT.

After an initial CT scan to rule out other causes of symptoms, a doctor may order an MRI to obtain more information.

An MRI can show signs of a stroke years or even decades after the stroke happens. Sometimes, a person may not know they had a stroke until a long time afterward.

MRI is the most accurate way to view signs of stroke inside the brain, but a CT scan is often faster and more widely available. Medical professionals may use CT first in people with suspected stroke and MRI later on to get more detailed images.