St. Louis, Aug. 9, 1999 -- Putting a new twist on an imaging technique, researchers now are able to identify tiny, malformed blood vessels in the brain that usually are missed by traditional imaging tests. The results may lead to more appropriate treatment of children and adults affected by these rare malformations, which can cause seizures, strokes and other neurological problems if left untreated.
The brain relies on a dense network of arteries and veins to remain healthy. The arteries bring oxygen to fuel neural activities, and the veins remove waste products from the brain. However, some people are born with webs of abnormal blood vessels in the brain that can grow larger with time, or they develop these masses as they age. It is unknown how common the masses are because they are difficult to image and are rarely discovered until they produce neurological problems by leaking or pressing on brain structures.
Using a variation of traditional magnetic resonance imaging (MRI), researchers at Washington University School of Medicine in St. Louis were able to obtain detailed information on blood vessel malformations in nine of 10 patients suspected of having the abnormalities. Traditional MRI revealed abnormal vessels in only seven patients and failed to provide sharp enough images to detect the extent of lesions in two instances.
Benjamin C.P. Lee, M.D., associate professor of pediatrics and radiology, was lead author of the study, which is published in the August issue of the American Journal of Neuroradiology. He also is a diagnostic radiologist at St. Louis Children's Hospital. The variation of MRI used in the study was developed by a team of investigators at the medical school's Mallinckrodt Institute of Radiology.
The new imaging method is an offshoot of functional MRI, which also was developed at the medical school. Functional MRI highlights increased levels of oxygen in vessels within active regions of the brain. By processing computer data from this technique slightly differently, investigators in the radiology department developed the blood oxygen level-dependent (BOLD), technique, which they named "high resolution BOLD venography."
By detecting very low oxygen concentrations, HRBV visualizes veins and minute vessels called capillaries that connect arteries to veins. "This technique is so sensitive to the low oxygen content that it can pick up a signal that is smaller than the resolution of its images," Lee says. The structures also have low blood flow, a feature that is hard for other techniques to pick up.
The researchers used HRBV in the study to view capillary masses called telangiectasias in seven patients. The images were sharper than those seen with traditional MRI. More important, the new technique detected additional telangiectasias in two patients and visualized masses that had not yet started to bleed. In two other patients, the researchers saw other masses called cavernomas that were missed by traditional MRI, as is usually true with other imaging methods. These masses and telangiectasias occur in similar locations.
Lee notes that HRBV could aid the surgical treatment of cavernomas and telangiectasias. "Potentially, you could use information from these images to guide the removal of the intact lesions before they actually cause symptoms," he says.
HRBV also may one day provide a new way to image brain tumor activity, Lee notes. Active regions of tumors are likely to have more veins to carry away wastes than inactive regions. By visualizing the entire network of veins leaving a tumor, the new imaging method could help guide the biopsy tools used to collect samples of tumors.
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