Medically reviewed by Edward Tavel, MD, Medical Director · Last reviewed 22 August 2026
A stroke happens when blood flow to part of the brain is interrupted, leaving brain tissue without the oxygen it needs. There are two main types. An ischemic stroke, which accounts for the large majority of cases, occurs when a clot or narrowed vessel blocks blood flow. A hemorrhagic stroke occurs when a blood vessel bleeds into or around the brain. A related event, a transient ischemic attack or TIA, produces stroke-like symptoms that resolve on their own, often within minutes. A TIA causes no lasting damage in most cases, but it is an important warning sign and is evaluated with the same urgency as a stroke.
Stroke symptoms usually appear suddenly. The most recognised pattern is summarised as FAST: face drooping, arm weakness, speech difficulty, and time to call emergency services. Other sudden symptoms include numbness on one side of the body, confusion, trouble seeing, loss of balance, or a severe headache with no clear cause. A suspected stroke is a medical emergency. Call 911 immediately rather than waiting to see whether symptoms pass, and do not arrange imaging on your own. Treatments that restore blood flow are most effective within a narrow window after symptoms begin, so the time between onset and arrival at hospital genuinely affects outcome. Risk factors include high blood pressure, atrial fibrillation, diabetes, high cholesterol, smoking, and a family or personal history of stroke.
MRI has a particular strength in stroke imaging. Diffusion-weighted imaging, or DWI, detects the change in water movement that occurs in brain tissue during an acute ischemic stroke, and it can show that change within minutes of onset — often before anything is visible on other imaging. In an emergency setting this helps clinicians confirm a stroke and decide on treatment. In an elective screening setting the role is different. A whole-body or brain MRI performed for preventive reasons sometimes reveals small older infarcts or white matter changes that a person never knew about, sometimes described as silent strokes. These findings do not require emergency care, but they are meaningful, because they suggest vascular risk factors worth discussing with your physician. If you are interested in the imaging itself, you can read more about what a full body MRI can and cannot tell you about stroke risk, the conditions a whole-body scan can detect, or how we handle incidental findings on an MRI.
Frequently asked questions
What should I do if I think someone is having a stroke?
Call 911 straight away. Note the time symptoms started, because that determines which treatments are available. Do not drive yourself, wait for symptoms to improve, or seek a scan independently. Emergency care is the correct path.
What is a silent stroke?
A silent stroke is an area of old damage found on imaging in someone who never noticed symptoms. It is reasonably common with age. It is not an emergency, but it does indicate vascular risk that is worth reviewing with your physician.
Can an MRI show an old stroke?
Yes. Older infarcts leave characteristic changes in brain tissue that remain visible long after the event. Radiologists can usually distinguish older damage from a recent stroke by how the tissue appears on different MRI sequences.
Does a normal brain MRI mean I will not have a stroke?
No. Imaging describes the brain as it is on the day of the scan. It cannot rule out a future event, and it does not replace management of blood pressure, cholesterol, heart rhythm, and other risk factors with your physician.
Why is MRI used rather than CT for some strokes?
CT is fast and excellent at detecting bleeding, so it is often the first test in an emergency. MRI with diffusion-weighted imaging is more sensitive to early ischemic change and to small strokes, so the two are frequently used together.
Sources
A whole-body MRI at MRI Wellness looks at the brain, spine, chest, abdomen and pelvis in a single session, without radiation or contrast dye. No referral is needed.
