New guidelines: MRI outperforms CT for stroke diagnosis
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"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," stated lead author Peter Schellinger, MD, with the Johannes Wesling Clinical Center in Minden, Germany.
Although CT is the de facto standard for stroke diagnosis, its sensitivity estimates for ischemic stroke range from 12 percent to 92 percent, with an overall sensitivity estimate of 40 to 60 percent for the six-hour time window. Newer MRI techniques, specifically diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI), may provide a practical and feasible way to improve diagnostic yield, researchers hypothesized.
A multi-disciplinary team comprised of neurologists, neuroradiologists and radiologists analyzed relevant literature from 1966 to January 2008 to evaluate the diagnostic and prognostic value of DWI and PWI.
The most compelling evidence originated with a study that assessed the accuracy of DWI versus CT in 356 consecutive patients presenting to a hospital emergency department over an 18-month period in whom the emergency physician diagnosed possible acute stroke, wrote the authors. Two neuroradiologists and two stroke neurologists blinded to clinical information and CT-DWI pairings independently interpreted the scans.
Among the 221 patients imaged within 12 hours, most readers correctly diagnosed acute ischemic stroke by MRI more often than by CT (94 vs. 22 percent). The odds ratio and its 95 percent confidence interval justified the recommendation for DWI over 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. Schellinger said studies have proven the importance of using MRI in emergency rooms, but adds that doubts still exist surrounding the use of stroke MRI scans in clinical settings.
"This guideline gives doctors clear direction in using MRI first, ultimately helping people get an acute stroke diagnosis and treatment faster. However, one situation in which CT may still be used first is when a person needs 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. Otherwise MRI should be used first."
Future research is needed, concluded researchers, who cited the need for prospective, well-designed studies on the diagnostic utility of PWI in acute stroke.