Physicians should use a diffusion MRI scan to diagnose stroke instead of a CT ( computerised tomography ) scan, according to a new guideline from the American Academy of Neurology. The guideline is published in the Neurology.

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.

A majority of strokes are ischemic, caused by lack of blood flow in the brain, usually due to a blockage or a blood clot. The window for treatment to reverse the damage from an ischemic stroke is measured in hours.

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

According to the guideline, diffusion MRI should be considered more useful than a CT scan for diagnosing acute ischemic stroke within 12 hours of a person’s first stroke symptom. In one large study, among others, that was reviewed for the guideline, stroke was accurately detected 83 percent of the time by MRI versus 26 percent of the time by CT.

In addition, the guideline found MRI scans more accurately detected lesions from stroke and helped identify the severity of some types of stroke or diagnose other medical conditions with similar symptoms.
Studies have proven the importance of using MRI in emergency rooms but doubts still exist surrounding the use of stroke MRI scans in clinical settings.

One situation in which CT may still be used first is when a person needs an emergency injection of intravenous thrombolytic 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.

Source: American Academy of Neurology, 2010

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