blood vessels and an initial CT scan is taken to show where the blood is flowing and identify any problem areas.
Next, diamox is injected and left to circulate for 15 minutes to dilate the blood vessels. A second CT scan is then taken. This allows the radiologist to calculate what is known as cerebral vascular blood reserve, which gives a precise measure of how much blood is flowing through the vessels and pinpoints areas of problem flow.
"Our initial findings suggest that cerebrovascular reserve testing could play a key role in determining which patients should get revascularization surgery and guiding graft placement," says Vagal, assistant professor of radiology at UC and neuroradiologist at University Hospital.
When the vessels of a normal brain are given stress or "challenged," blood flow should increase. In patients with chronic blocked blood flow (occlusive disease), the vessels are already fully dilated and cannot expand further to accommodate increased blood flow. Blood cannot pass through the blocked vessel, which can lead to an increased risk of stroke.
By conducting the diamox challenge test preoperatively, the team hopes to reduce the chances of future strokes by identifying potential blood flow problems earlier.
"Having this information is critical to determining next steps in patient care—specifically whether the patient should have revascularization surgery, which is a complex and delicate undertaking," adds Vagal.
Vagal says perfusion CT technique and the diamox challenge test are not new concepts. The novelty lies in using them together with more precise scanners and faster methods for gathering this collective data.
"Now we can collect comprehensive imaging data that can become a reliable information resource for the neurosurgeons advising patients on their care," she says.
So far, the UC neuroscience team has used this combined imaging technique to evaluate 60 adult patients with complex cerebrovascular diseases, including 20 with moyamoya.
Treatment for moyamoya is not widely offered and involves surgically bypassing the blocked arteries. Mario Zuccarello, MD, a UC professor of surgery and neurosurgeon with the Mayfield Clinic, performs that surgery—known as an extracranial-intracranial bypass—which involves connecting the superficial temporal artery from the scalp outside the skull to the middle cerebral artery inside the skull.
Preliminary data on this imaging technique received the Summa Cum Laude Award at the 2008 American Roentgen Ray Society conference.
David White, MD, Rhonda Strunk and James Leach, MD, participated in this research with Vagal and Zuccarello.