The Doctor Is In

Here’s looking at you: stroke imaging

By R. Kent Hutson, MD

Stop Stroke Saturday
Learn more about stroke at this free seminar.

Call 423-778-LINK (5465) to register.
Light breakfast and lunch provided.

East Campus:
Saturday, May 3
9:30 a.m. – 2 p.m.

When most people think about stroke, it probably goes something like this: “I hope I never have one.”

After all, strokes can kill. And they are very common in our area. In fact, Erlanger treated more than 900 stroke patients between July 1, 2006, and June 30, 2007. Using a combination of specialized images of the brain, physicians can accurately and quickly see a stroke and decide on the best way to treat the stroke as it happens – hopefully reversing the damage caused to the brain.

Asking the right questions The treatment of a new stroke depends on a few critical questions:

Is there a blood clot?If a blood clot in the artery caused the stroke, then clot-busting medicines or specialized catheters can be used to break down the blood clot and restore blood flow to the brain.

Where is the blood clot and how big is it? The type of therapy used for a particular person with a particular stroke depends on how large the clot is and where the clot is located. For example, a very small clot in a small artery might be better treated with medication, but a large clot in a large artery might require a special catheter to pull the clot out of the artery.

To help answer these key questions, physicians at Erlanger use the latest imaging to view the brain.

Answers in images A computed tomographic (CT or CAT) scan uses a spinning x-ray tube to create images that are slices of the brain. Modern CT scanners can scan the brain in seconds. The entire procedure – including moving someone from the stretcher to the scanner bed – can be performed in minutes.

If this quick overview finds bleeding in the brain, any kind of clot-busting medicine would only make things worse. Occasionally, someone who appears to be having a stroke might also have something else, like a brain tumor. This will also be seen with the screening CT scan.

If the stroke is treatable, the patient immediately receives a contrast solution for more extensive testing. The contrast (an iodine compound) is injected into an arm vein, travels through the blood vessels, and can be seen in the arteries of the brain.

Two different types of images can be made – CT angiography and CT perfusion.

In CT angiography (CTA), the brain is imaged as the contrast is passing through the arteries. A blood clot in the artery will appear dark, while the contrast turns the rest of the artery white.

In CT perfusion (CTP), the brain is imaged as the contrast passes through the brain tissue. Using specialized analysis software, the rate of blood flow through the brain is calculated to determine how much of the brain is starved for blood and how big the stroke might be.

The CT, CTA, and CTP studies can all be completed in less than 10 minutes, giving physicians the information they need to treat a stroke in a very short time.

However, CT doesn’t show exactly where and how big the stroke is. To get a better idea of how much brain has been damaged, we turn to Magnetic Resonance Imaging (MRI).

MRI uses a large magnet and radio waves to image the brain. For stroke, a special technique called Diffusion Weighted Imaging (DWI) can be used with MRI to show precisely how much brain is involved.

DWI works by detecting the difference in the speed of the water in the brain. During normal brain fuction, cellular pumps keep excess water out of the cell. But when blood flow to an area of the brain stops because of a stroke, the pumps stop working and water rushes into the cell. The water outside the cell that was moving freely is more restricted inside the cell, resulting in an overall slower movement (diffusion) of water in the affected part of the brain. MRI with DWI detects this water shift. If nothing is done to re-establish blood flow, these starving cells will die.

Imaging techniques give doctors fast, reliable information to help them choose the best treatment for stroke patients.

R. Kent Hutson, MD, board-certified radiologist, is Chief of Radiology Services for Erlanger. He is also an Associate Professor and Chair of the Radiology Department with the UT College of Medicine Chattanooga. For more information, contact Erlanger’s physician referral line at 423-778-LINK(5465).