Magnetic resonance imaging of the brain helped to determine the duration of a stroke in patients with unknown onset time, and thereby improved the ability to identify patients who were eligible for thrombolysis in a small retrospective study.
The study, published online in the Nov. 2 issue of Radiology, is an early look at ways of using MRI to manage all stroke patients urgently, "not just those patients with a known onset of symptoms," Dr. Catherine Oppenheim, lead investigator, said in a statement from the Radiological Society of North America, which publishes Radiology.
The study included 77 men and 53 women with a mean age of 65 years who presented consecutively between May 2006 and October 2008 with acute ischemic stroke with known onset time. They underwent 1.5-T MR imaging within 12 hours of symptom onset.
Imaging ratios in 63 patients who underwent imaging within 3 hours of symptom onset differed significantly from those in 67 patients who underwent imaging more than 3 hours after symptom onset, allowing first author Dr. Mina Petkova of Université Paris (France) Descartes and colleagues to identify which patients were within the 3-hour window that deemed them eligible for thrombolysis with tissue plasminogen activator (tPA).
Only 13 of those patients were imaged 3-4.5 hours after onset. (Since the fall of 2008, the American Heart Association, the American Stroke Association, and the European Stroke Organization have recommended that the tPA treatment time window be expanded to within 4.5 hours after stroke onset.)
Specifically, the fluid-attenuated inversion recovery (FLAIR) ratio showed a positive correlation with time from symptom onset, and the investigators demonstrated that this ratio could identify patients imaged within 3 hours of symptom onset with 90% sensitivity and 92% specificity when a 7% FLAIR ratio cutoff was used. Additionally, visual inspection of FLAIR and diffusion-weighted (DW) images was able to identify stroke imaged within 3 hours with 94% sensitivity and 97% specificity, the investigators found (Radiology 2010 Nov. 2 [doi:10.1148/radiol.10100461]).
The findings based on both these quantitative and qualitative analyses could have implications for the approximately 25% of stroke patients who don’t know, or who are unable to communicate, when their stroke symptoms began, according to Dr. Oppenheim, professor of radiology at the university.
That is, brain MRI could be used as a surrogate marker of stroke age in cases when the time of stroke onset is unknown or uncertain to help identify those who are within "the time window for which intravenous thrombolysis has proved effective, is approved, and is recommended by international guidelines," the investigators wrote.
One implication of the finding that 1.5-T MR imaging provides reliable stroke age estimation is a potential increase in the number of patients eligible for thrombolysis.
"Our results confirm that further, prospective multicenter studies in which the safety of thrombolysis is assessed in patients with unknown stroke onset time should integrate, among other things, parameters used to estimate stroke age on the basis of FLAIR imaging," the investigators concluded.
The investigators had no financial relationship to disclose.