ANN ARBOR A newly published report from the University of Michigan show that an innovative type of brain scan can quickly tell doctors exactly where blood problems lie, and help them decide how to restore blood flow. And it can be done on scanners found in many hospitals.

That’s the conclusion of two new papers published in the June issue of the journal Radiology by a team from the UM Health System. The researchers detail the many potential uses of a technique called perfusion CT, including their own research results and data from a few other teams worldwide.

The UM team, which has used perfusion CT clinically for several years, hopes their new findings and their comprehensive review of the literature will help many other hospitals decide to adopt the life-saving technique.

Perfusion CT scans can be made by any modern computed tomography machine, with help from special software. Several other brain-scanning techniques that can also reveal blood flow, such as PET, SPECT or xenon CT, require special equipment not found in many hospitals, cost a great deal or are more arduous for patients.

“It’s still a relatively new technique, but it could be adapted to any newer-generation CT scanner and be used to image acute and chronic cerebrovascular conditions,” says Ellen Hoeffner, M.D., the lead author of one of the two new papers and an assistant professor in the Department of Radiology in the U-M Medical School. “It still isn’t completely validated for use in some conditions, but more research will help.”

The scan is made by passing X-rays through the brain, just like a regular CT scan. But in addition to revealing the structure of brain tissue, perfusion CT also shows how much blood is present in the brain and how quickly it is moving. This is done by scanning the patient several times every few seconds before, during and after the intravenous delivery of an iodine-containing contrast agent that absorbs the X-rays.

Often, surgeons will try to open or go around extremely clogged or narrowed carotid arteries, using procedures such as angioplasty, carotid endarterectomy or brain bypass. Or, if a nearby tumor must be removed, they may decide to close one carotid artery off for good, and let the other one feed the brain. But first they must test how well blood is getting through to the brain, and how the patient’s brain will do if there’s a temporary or permanent closure of the artery. Perfusion CT can help with both of these important tasks, and determine who might be helped – or harmed – by surgery.

To measure how strained the brain blood flow system is, a quality called cerebrovascular reserve, the perfusion CT scan is done after patients receive a dose of the drug acetazolamide to dilate their blood vessels and maximize flow. Those patients whose vessels don’t dilate in response to acetazolamide, because they’re already maximally dilated and letting as much blood through as they can, are most likely to benefit from a blood flow augmentation procedure.

Perfusion CT can also help during a balloon-test occlusion, in which doctors insert a tiny balloon into the narrowed blood vessel, inflate it to stop blood flow briefly, and measure any changes in brain activity.
This shows how well a patient’s brain could withstand surgery or one carotid closure.

In new results from eight patients, the U-M team shows that perfusion CT gave valuable information on patients who pass the balloon test but whose brain scan shows low blood flow that might not be sufficient if the closure is permanent. They say it may even be able to help predict which patients might go on to suffer a stroke after having one of their carotid arteries permanently closed.

Perfusion CT may also help when a patient has a stroke that’s caused by blockage of blood supply to part of the brain, often because a clot or piece of plaque has lodged itself in a small blood vessel. This kind of stroke, called ischemic, is the most common form, accounting for 80 percent of the 730,000 strokes that occur nationally each year.