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Dartmouth Medical School Dartmouth-Hitchcock Medical Center


Stroke study may prove very timely

By Amos Esty

Risto Kauppinen is devising a method to determine the time a stroke took place.

Every second counts in treating a stroke, but watching the clock isn't just a matter of administering treatment quickly. Doctors must first determine what kind of stroke a patient suffered. Then, in the case of an ischemic stroke—one caused by a blood clot—they need to pin down when the blockage occurred. A new technique being studied by DMS radiology researcher Risto Kauppinen, M.D., Ph.D., may help with that crucial step. He's using magnetic resonance imaging (MRI) to examine post-stroke changes in the brains of rats; the rate of change appears to yield a timeline showing when the stroke began.

Onset: This is important because the medications currently available for ischemic strokes can only be used within several hours of the onset of the stroke. Otherwise, the risks of bleeding caused by the drugs outweigh their potential benefits. If it's not possible to determine whether a patient is within that time window, the potentially life-saving drugs can't be used.

In the hope of solving this problem, Kauppinen and colleagues induced ischemic strokes in rats and used MRI to examine the rats' brains up to six hours later, comparing tissue in two parts of the brain affected by the strokes to tissue in an unaffected part of the brain. They found that a measurement called T1 relaxation time increased steadily in the affected tissue as time passed after the onset of a stroke, but it stayed the same in unaffected tissue. So, given specific T1 values from similar rats that had suffered a stroke, the researchers could arrive at a fairly precise estimate of when the stroke began.

Flow: They did encounter one complication. One affected area of the rats' brains maintained some residual blood flow for a few minutes after the onset of a stroke, so for about 10 minutes its T1 values appeared to be the same as those of unaffected tissue.

There would be still other difficulties to overcome before this technique could be considered for use in humans, because, Kauppinen says, "the human brain is much more complicated in terms of anatomy than the rat brain." But he hopes next to try the technique in larger animals, and, eventually, in humans as well.

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