A computed tomography scan (better known as a CT scan or CAT scan) is often one of the first tests done in a stroke evaluation. CT scans can show areas of abnormalities in the brain, and can help determine if these areas are caused by insufficient blood flow (ischemic stroke), a ruptured blood vessel (hemorrhage), or another issue entirely.

It’s important to note that CT scans are not always the final word on whether a stroke has taken place. Strokes may not be seen on a CT scan for several reasons. It can sometimes take several hours for the brain to appear abnormal after the onset of stroke. The affected region may also be a part of the brain that CT scans do not image well, such as the cerebellum or the brainstem. Depending on the results, your physician may issue additional tests, including an magnetic resonance image (MRI).

CT angiography
This test is performed using the same machine (CT scanner), but is designed to evaluate the major arteries providing blood to the head/brain and neck. X-ray contrast (a salt of iodine) is injected through a peripheral (arm/hand) IV line, which causes the arteries to become very visible on the scan. Blockage (occlusion) or other abnormalities of the arteries can easily be seen on this scan, which is very important for guiding treatment.

CT perfusion
This test is performed using the same machine (CT scanner), but is designed to evaluate blood flow to the brain tissue at the capillary level. X-ray contrast (a salt of iodine) is injected through a peripheral (arm/hand) IV line. This technique provides information necessary to determine whether salvageable brain tissue exists, in order to guide appropriate treatment, especially in the extended time window from 6 to 24 hours after the onset of symptoms.

How CT scans work

A CT scan uses X-rays to take pictures of your skull and brain that are then used by computers to create an image of a cross-section (or “slice”) of the brain. These images can show the location and size of brain abnormalities caused by blood clots, tumors, blood vessel defects and more. CT scans can be an ideal method of determining whether a stroke is ischemic or hemorrhagic, because they often appear distinct from one another in these images.

During a CT scan, the patient lies in a tunnel-like machine while the inside of the machine rotates, taking X-rays of the head, brain and skull from a variety of angles. The process generally takes between 20 minutes and an hour and is painless with few side effects.