SAN DIEGO—Use of fluid-attenuated inversion recovery (FLAIR) imaging can help estimate the onset of acute ischemic stroke within six hours, which may enable more patients to receive thrombolytic therapy, researchers reported at the 2009 International Stroke Conference.
Junya Aoki, MD, of the Department of Stroke Medicine, Kawasaki Medical School in Kurashiki, Japan, and colleagues evaluated 336 patients (207 males; median age, 74) with known stroke onset times within 24 hours. Fifty-three patients underwent multiple MRI examinations, yielding a total of 389 MRI scans that were analyzed. All patients were examined with use of FLAIR and diffusion-weighted imaging. Diffusion-weighted imaging and FLAIR results were each defined as positive when they detected a new hyperintense lesion, and negative when no hyperintense signal was shown.
Participants were categorized into subgroups based on time from stroke onset to imaging. A total of 162 studies (42%) were conducted within zero to three hours of stroke onset, 109 studies (28%) were within three to six hours of stroke onset, and 118 studies (30%) were conducted within six to 24 hours of stroke onset. With respect to stroke subtypes, 60 studies revealed small vessel disease, 33 patients had large artery disease, and 155 had cardioembolic disease; in 141 cases, the cause of stroke was undetermined.
Dr. Aoki and colleagues found that 86% of patients who underwent MRI within three hours of stroke onset had a positive diffusion-weighted imaging result, compared with a 14% FLAIR-positive result for those within the same time group. About 99% of those who underwent MRI between six and 24 hours of stroke onset had a positive diffusion-weighted imaging result, compared with 88% who had a positive FLAIR result within the same time frame.
When a FLAIR result was negative and a diffusion-weighted imaging result was positive, there was an increased likelihood that stroke onset had occurred within three hours of testing, noted the investigators. However, when FLAIR was positive and diffusion-weighted imaging was negative, the stroke most likely occurred more than six hours previously.
The ability of FLAIR to accurately detect stroke onset gradually increased in accordance with the intervals from onset to MRI, according to Dr. Aoki. “When FLAIR findings were negative, with or without diffusion-weighted imaging–positive results, the probability of onset-to-image time of zero to three hours was 46%, and zero to six hours was 73%,” he reported. Within 4.5 hours, the probability of onset-to-image time was 63%.
In a second analysis, the investigators excluded 63 studies of patients with infratentorial infarcts, 81 studies of those who had isolated infarctrcts in the supratentorial lesion that were less than 5 mm. Ultimately, 234 MRI studies were analyzed.
“When we focused on patients with large infarcts (greater than 15 mm) in a specific region of the brain, the probability of stroke onset-to-image time of zero to three hours was 59%, within 4.5 hours it was 77%, and zero to six hours was 94%,” Dr. Aoki stated.
“FLAIR should be useful for presuming the time of stroke onset,” he concluded.
—Colby Stong