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.
Hoeffner notes that commercially available computer software can calculate blood flow rates from this raw scan information. And doctors can zoom in on regions of interest: so, for example, the blood flow in the area fed by a clogged carotid artery on one side of the brain can be compared with the flow in an area fed by the other carotid artery, on the opposite side of the brain.
Clogs in the carotid arteries are caused by the same cholesterol-laden plaque that can cause chest pain and heart attacks when it occurs near the heart. In the brain, these blockages can cause problems with thinking or vision and are a major risk factor for the most common kind of stroke.
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
Contact: Kara Gavin
University of Michigan Health System