Diffusion MRI scans are better than CT scans at diagnosing strokes, according to a new guideline from the American Academy of Neurology.

In one large study, among many that were reviewed for the guideline, stroke was accurately detected 83 percent of the time when an MRI was used compared to 26 percent of the time when a CT was used. MRI scans also detected lesions from strokes more accurately and helped identify the severity of some types of stroke.

"While CT scans are currently the standard test used to diagnose stroke, the Academy's guideline found that MRI scans are better at detecting ischemic stroke damage compared to CT scans," Peter Schellinger, M.D., from the Johannes Wesling Clinical Center in Minden, Germany, was quoted as saying.

Most strokes are ischemic, which means they are caused by lack of blood flow to the brain. The window for treatment in these strokes is just hours.

"This guideline gives doctors clear direction in using MRI first, ultimately helping people get an acute stroke diagnosis and treatment faster," Schellinger said. "However, one situation in which CT may still be used first is when a person needs an emergency injection of drug therapy to break up blood clots, if MRI is not immediately available, to avoid delays in starting this treatment. MRI can be added later if more information is needed. Otherwise, MRI should be used first."

CT scans are a specialized kind of X-ray of the brain, while MRI uses magnetic and radio waves to show clearer images of the brain tissue. Diffusion MRI measures molecular water motion in the tissue, showing where water diffusion is restricted and brain damage has occurred.


SOURCE: American Academy of Neurology, July 12, 2010