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Release:Oct. 4, 2002

NOTE TO EDITORS: Ryken will participate in a news conference about this subject from 10:30 to 11:30 a.m. (Pacific Time) Thursday, Oct. 8 in the ACS press conference room in the North Hall registration area of the Moscone Convention Center in San Francisco.

UI neurosurgeons to present findings at national meeting

University of Iowa Health Care neurosurgeons will discuss research findings from their study of an advanced technology that may enhance outcomes for patients with brain tumors during the upcoming American College of Surgeons Clinical Congress in
San Francisco Oct. 6-10.

The commercially available computerized image-guided neurosurgery system links sonograms with magnetic resonance imaging (MRI) scans to produce a highly detailed roadmap of a patient's brain. As a result, the surgeons are able to track the actual movement of surgical instruments as they operate on brain tissue, thus increasing their assurance that they have completely excised brain tumors.

"We don't have to wait for a postoperative image to know if we removed all of a tumor. We can be more confident when we walk out of the operating room that we have accomplished what we set out to do," said Timothy C. Ryken, M.D., UI associate professor of neurosurgery.

The image-guided surgery system takes advantage of the immediacy of ultrasound and the precision of MRI. Ultrasound is an inexpensive way of obtaining imaging information during surgery. Surgeons can pass an ultrasound probe directly over the surgical field and obtain real-time images of a patient's anatomy, but the resolution of ultrasound images is poor. Because of the grainy quality of sonograms, surgeons often cannot distinguish between normal and abnormal tissue.

"Some tumors are not very discrete or easily recognized by ultrasound alone," Ryken explained.

MRI performed with intravenous contrast media is highly definitive. Contrast material (a chemical that is taken up by, and alters the appearance of, abnormal structures in the body) travels to and enhances the sites of brain tumors so they appear as white masses on MRI scans. However, having a dedicated MR scanner to identify brain tumors in patients during surgery is extremely expensive.

Furthermore, MR imaging during surgery requires surgeons to use special, non-metallic instruments. Therefore, surgeons commonly have to rely on slices of static MR images that were obtained preoperatively to identify tumors.

With the computerized image-guided neurosurgery system that marries ultrasound and MRI, Ryken and his colleagues can view both intra-operative sonograms and preoperative MRI data at the same time on the same operating room computer workstation. The system's software reconstructs the information from the MRI that corresponds to the spot where the surgeon is holding the ultrasound probe.

The system also compensates for the inevitable shift of tissue that occurs during brain surgery, which interferes with the interpretation of preoperative MRI scans and intra-operative findings.

"When we have a patient in the MRI scanner, the brain is fixed and solid within the cranium. During surgery, we have to remove a part of the skull to reach the brain. Depending on the position of the craniotomy, the degree of atmospheric pressure and the severity of the patient's condition, brain tissue may bulge out or sink away. The tumor may now be two to four centimeters away from where we would have predicted it to be, based on the preoperative MRI scan," Ryken said.

Imaging information from the system also altered the surgical approach to treatment in some patients, Ryken added.

"There were times when I thought I was finished resecting a tumor but then went back and took some more tissue out because of what the ultrasound and MR images showed," he said.

Ryken and his colleagues have performed approximately 200 intra-cranial procedures using the intra-operative image-guided system.

"The preoperative MRI and intra-operative ultrasound aren't linked perfectly, so the system doesn't replace the surgeon’s judgment. It is still a tool," Ryken emphasized. He also noted that researchers still need to determine how the system will translate into improved long-term outcomes for patients.

Manali Barua, M.D., and John Haller, Ph.D., were also involved in the study of patients with metastatic brain tumors.

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