CT Perfusion Efficacy Diagnosing Acute Ischemic Stroke Demonstrated in Study

New research shows that computed tomography (CT) perfusion imaging--a technology that measures blood flow and is available to most hospitals--may dramatically improve fast and accurate stroke diagnosis, enabling physicians to provide more targeted care and helping avoid potentially life-threatening complications of "clot buster" therapy.

The study, performed by researchers from West Virginia University Health Sciences Center (WVU; Morgantown, USA), is the largest to date of the lifesaving technology's usefulness in diagnosing stroke and staging its treatment.

The study, published in the October 2008 issue of The Journal of Emergency Medicine, demonstrated that using CT perfusion to diagnose stroke may be as valuable as magnetic resonance imaging (MRI)-- an imaging technology that takes far longer to use at a time when every second counts before treatment is initiated. The CT technology allows clinicians to identify patients who are suitable candidates for treatment, utilizing either clot busting medicines or clot retrieval devices.

WVU researchers believe this research could change national protocols on how stroke patients are triaged and potentially extend treatment opportunity beyond the three-to-six hour window. "Our study reveals that the widespread use of CT perfusion is a practical way to help busy emergency departments save precious time in stroke diagnosis, target treatment, and reduce the risks of inappropriate thrombolytic use," said Ansaar T. Rai, M.D., assistant professor of neuroradiology and neurointerventional radiology at WVU. "CT perfusion was able to pinpoint strokes with high levels of accuracy, particularly the major intracranial vessel strokes that result in more devastating outcomes."

Key findings of the study include: (1) CT perfusion has a very high sensitivity rate (92%) for detecting infarcts due to a major vessel occlusion, the most debilitating kind of stroke. (2) The specificity rate for detecting acute ischemic stroke was perfect (100%). The researchers, who have utilized CT perfusion in clinical practice with the largest reported number of suspected stroke victims of any center in the United States, also reported that the average time between emergency room neurologic exam and CT scan was 35 minutes.

Under U.S. National Institutes of Health guidelines, hospitals should administer tPA (a clot-busting, or thrombolytic, drug) to patients within a three-hour window of stroke onset. After six hours, the medicine is considered too risky, due to the possibility of a deadly hemorrhage. Just 1-2% of stroke patients receive clot busters. Experts believe this is due largely to perceived risks and uncertainty about whether patients are actually having strokes. A fast, accurate, and accessible means of diagnosis of could change these statistics.

To determine the utility of CT perfusion, Dr. Rai and colleagues conducted a retrospective analysis with 867 patients who underwent CT perfusion as part of a routine evaluation for suspected stroke at WVU's Ruby Memorial Hospital. Only patients who had a follow-up MRI scan within one week (422) were included in the analysis. CTP abnormalities in these patients were compared with subsequent diffused weighted image (DWI) abnormalities seen on follow-up MRI scans.

MRI scans are considered the gold standard for post-stroke analysis, but they are rarely performed and usually are impractical because: they take 30 minutes to perform, require a stroke patient to be still to capture clean images, require doctors to check for metal in the patient's body (which may be impossible if the patient is not verbal) and the MRI units themselves are frequently understaffed or not located near the emergency room.

CT perfusion provides clear advantages because most hospital emergency rooms use CT scanners for other purposes, they take one to two minutes to scan, and provide clear images even if a patient cannot lie perfectly still. Most hospitals need only to buy software (at relatively low cost) to upgrade their systems and institute training programs. Moreover, CT angiograms are necessary to locate blockages--and these can be done simultaneously with the perfusion CT, saving valuable time.

The study findings may have the greatest effect on rural care, but also will help crowded urban centers utilize resources to improve diagnostic times and extend the life of imaging equipment. In addition, the study shows that a hospital and emergency department where comprehensive services are available can potentially serve as the nexus of a tele-stroke network in triaging patients and increasing outcomes.

Related Links:
West Virginia University Health Sciences Center