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(Stroke. 2006;37:883.)
© 2006 American Heart Association, Inc.

Original Contributions

Stroke Onset Time Using Sodium MRI in Rat Focal Cerebral Ischemia

Stephen C. Jones, PhD; Alexander Kharlamov, MD, PhD; Boris Yanovski, MD; D. Kyle Kim, PhD, MD; Kirk A. Easley, MS; Victor E. Yushmanov, PhD; Scott K. Ziolko, BS Fernando E. Boada, PhD

From the Departments of Anesthesiology (S.C.J., A.K., B.Y., V.E.Y.) and Neurosurgery (D.K.K.), Allegheny-Singer Research Institute, Pittsburgh, Pa; Biostatistics Consulting Center (K.A.E.), Rollins School of Public Health, Emory University, Atlanta, Ga; and Positron-Emission Tomography Center (S.K.Z.) and Magnetic Resonance Research Center (F.E.B.), Department of Radiology, University of Pittsburgh School of Medicine, Pittsburgh, Pa.

Correspondence to Stephen C. Jones, PhD, Drexel University College of Medicine, Department of Anesthesiology, Allegheny-Singer Research Institute, 320 East North Ave, Pittsburgh PA 15212-4772. E-mail sjones{at}wpahs.org

Background and Purpose— Thrombolytic therapy with intravenous tPA must be administered within 3 hours after stroke onset. However, stroke onset time cannot be established in 20% to 45% of potential patients. We propose that the rate of increase of the brain concentration of sodium ([Na⁺]_br) after stroke, monitored using sodium MRI in a rat model of cortical ischemia, is linear in each individual animal, can locate the ischemic region, and can be used to estimate onset time.

Methods— After induction of focal cortical ischemia in rats under isoflurane anesthesia, [Na⁺]_br time course maps were acquired continuously on a 3 T whole body scanner from 2 to 7 hours after occlusion followed by T2-weighted proton images. Microtubule-associated protein-2 immunostained brain sections were used to verify the location of the infarct.

Results— The ischemic region identified with microtubule-associated protein-2 corresponded to the region of maximum [Na⁺]_br increase (P<0.001; n=5), and all of the animals demonstrated high linearity. [Na⁺]_br increased at a mean rate of 25±4.7%/h in ischemic tissue (P=0.013) but not in normal cortex (1.0±1.1%/h; P=0.42). The mean onset time error was 1±4 minutes (n=4).

Conclusions— These results of sodium MRI show that the region of maximum [Na⁺]_br increase corresponds to the ischemic region. Although [Na⁺]_br increases at a different rate in each animal, the increase is linear, and, therefore, onset time can be estimated. These findings suggest that this method can be used as a ticking clock to estimate time elapsed after vascular occlusion.

Key Words: cerebrovascular disorders • infarction, middle cerebral artery • MRI • sodium • stroke

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