CHICAGO -- A new technique for determining the rate of blood flow, developed by researchers at the University at Buffalo Toshiba Stroke Research Center, will enable neurosurgeons, using digital radiographic imaging, to characterize and treat cerebrovascular abnormalities called arteriovenous malformations (AVMs) more effectively.
The new method, called dual contrast injection, which has not been used elsewhere for this condition, was described today (Nov. 30, 1998) at the Radiological Society of American annual meeting in Chicago by lead researcher William Granger, a UB physiology and biophysics doctoral candidate.
Neurosurgeons with UB's Toshiba Stroke Research Center have used the procedure on 21 patients, with no complications.
An AVM is a tangle of fragile vessels in the brain or spinal chord that forms between an artery, which carries oxygen-rich blood to the brain, and a vein, which drains oxygen-depleted blood back to the lungs for replenishment. It creates a short-circuit between the two circulation systems, shunting blood directly from the artery into the vein, effectively bypassing the brain.
An AVM can leak or rupture if it isn't treated. The condition is thought to be congenital, and is diagnosed most frequently in young adults, Granger said.
One way of treating AVMs, and the method of choice of neurosurgeons at the UB Toshiba Stroke Research Center, is to seal off the entrances to the blood vessels nourishing the AVM, called feeding pedicules, with a glue-like substance. With the feeding pedicules sealed off, circulation resumes its normal path, full oxygenation of the brain is restored, and the threat of bleeding or stroke is eliminated.
For this technique to work maximally, neurosurgeons must be able to gauge the exact rate of blood flow through the AVM, so they can determine the transit time of the glue from the injection point to the site to be blocked. They then can formulate the gluing agent so it hardens at the proper point as it is carried along by the blood flow. This ensures that blood flow is blocked to the AVM without occluding the main artery or vein.
Current techniques for determining rate of blood flow use two approaches, both involving injecting a contrast medium into the AVM through a tiny catheter threaded through the large artery in the groin until it reaches the damaged area. The contrast medium is tracked via digital X-ray imaging.
One approach involves injecting a soluble contrast medium, which is effective in showing the internal contours of the vessel and its twists and turns, enabling neurosurgeons to determine distance to the AVM. But because the contrast medium dissolves and diffuses into the blood stream, it does not produce a clear leading edge necessary to track how fast the flow is moving.
An alternate approach uses a non-soluble contrast medium: small droplets of a poppyseed oil-based agent containing radioactive iodine. These droplets provide the necessary leading edge to provide precise information on speed of the flow. But because the contrast medium doesn't dissolve and fill the vessel, tracking the oil droplets alone provides no information on the path, or distance, the drop has traveled, which is necessary for determining the rate of flow.
Granger's idea was to administer both contrast media simultaneously. Dual contrast injection allows neurosurgeons or neuroradiologists to gauge both distance and time with one intervention. He said the technique has never been used elsewhere for determining the rate of blood flow in AVMs.
"The two methods together allow more exact means of determining rate of flow," Granger said. "We can determine the exact time for the glue to reach the arteriovenus junction. Our method is more accurate in determining flow velocity than either single soluble or non-soluble injections alone."
Additional members of the research group were Afshin A. Divani, doctoral candidate in mechanical and aerospace engineering; Stephen Rudin, Ph.D., professor of radiology and physics; Ajay K. Wakhloo, M.D., associate professor of neurosurgery; Baruch B. Lieber, Ph.D., associate professor of mechanical and aerospace engineering, and Daniel R. Bednarek. Ph.D., associate professor of radiology and physics, all of UB.
The research was funded by a grant from Toshiba American Medical Systems.
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