New Super-Sensitive MRI Gives Clearer Picture of Stroke in Action
Feb. 11, 2000 (New Orleans) -- One of the difficulties that has plagued treatment of stroke is the inability of physicians to get a good clear image of the brain as damage is occurring. That, however, may be changing with the arrival of a new type of highly sensitive MRI called diffusion-weighted imaging (DWI).
This high-tech approach to diagnosis allows a neurologist to track the flow of water through brain tissue. The water perfusion is an accurate measure of the size and location of the stroke, say stroke experts meeting here at the 25th Annual International Stroke Conference.
At a press conference devoted to the latest studies on imaging, all the presenters agreed that DWI appears to be a much more sensitive imaging option than MRI, especially during the early hours of acute stroke. But the experts were divided over whether the new, very expensive technology should be used in place of CT as a standard of care. Currently, when a patient arrives at a hospital emergency room with stroke symptoms, a CT scan of the head is used to help physicians determine if a stroke is in progress and if the patient is a candidate for the use of clot-busting drugs.
David C. Tong, MD, assistant professor of neurology and neurological sciences at the Stanford Stroke Center in Palo Alto, Calif., tells WebMD that based on good, prospective clinical trials "a negative CT is the standard of care, so I don't want to give the impression that DWI should replace CT at this time."
DWI is essentially a "faster, more sensitive MRI that is a very sensitive technique for measurement of early ischemia," says Tong. Centers can either have an MRI fitted with new magnets to perform DWI or can buy a new MRI since new systems all come with the DWI option, says Tong. Either overhauling the existing MRI or purchasing a new machine can cost "in the millions," he says.
A cheaper option -- costing about $100,000 -- is a computer enhancement that can be added to an old MRI. The computer upgrade, however, doesn't give the speed that new magnets or a new machine offers and may actually be too slow to be useful, says Tong.
The use of DWI to evaluate a series of 39 patients "resulted in both a change in diagnosis and change in management." Though that finding is persuasive, it still falls short of the type of large clinical trials that support CT, according to Tong.
The other studies, all discussed at the press conference, were also highly favorable. Candice J. Perkins, MD, a neurology fellow at State University of New York at Stony Brook, says that among a series of stroke patients who arrived at the hospital up to 6 hours from the onset of stroke, 77% "had lesions that were not detectable by traditional imaging but were visible using DWI." Perkins tells WebMD that traditional imaging refers to MRI. She says, too, that of the 77% with only DWI visible lesions, "half had salvageable brain tissue."