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(Stroke. 2006;37:1211.)
© 2006 American Heart Association, Inc.

Original Contributions

Ischemic Thresholds for Gray and White Matter

A Diffusion and Perfusion Magnetic Resonance Study

Shuji Arakawa, MD, PhD; Peter M. Wright, FRACP; Masatoshi Koga, MD, PhD; Thanh G. Phan, FRACP; David C. Reutens, MD, FRACP; Indra Lim, BSc; Marveyles R. Gunawan, BComp; Henry Ma, MBBS, FRACP; Nilupul Perera, MBBS, MD; John Ly, MBBS, FRACP; Jorge Zavala, MD; Gregory Fitt, FRANZCR Geoffery A. Donnan, MD, FRACP

From the National Stroke Research Institute (S.A., P.M.W., M.K., T.G.P., D.C.R., I.L., M.R.G., H.M., N.P., J.L., J.Z., G.A.D.), Department of Medicine (D.C.R., G.A.D.), University of Melbourne; and Department of Radiology (G.F.), Austin Hospital, Melbourne, Australia.

Correspondence to Professor Geoffrey A. Donnan, National Stroke Research Institute, 300 Waterdale Rd, Heidelberg Heights, Victoria, Australia 3084. E-mail gdonnan{at}unimelb.edu.au

Background and Purpose— Although gray matter (GM) and white matter (WM) have differing neurochemical responses to ischemia in animal models, it is unclear whether this translates into differing thresholds for infarction. We studied this issue in ischemic stroke patients using magnetic resonance (MR) techniques.

Methods— MR studies were performed in patients with acute hemispheric ischemic stroke occurring within 24 hours and at 3 months. Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and apparent diffusion coefficient (ADC) were calculated. After segmentation based on a probabilistic map of GM and WM, tissue-specific diffusion and perfusion thresholds for infarction were established.

Results— Twenty-one patients were studied. Infarction thresholds for CBF were significantly higher in GM (median 34.6 mL/100 g per minute, interquartile range 26.0 to 38.8) than in WM (20.8 mL/100 g per minute; interquartile range 18.0 to 25.9; P<0.0001). Thresholds were also significantly higher in GM than WM for CBV (GM: 1.67 mL/100 g; interquartile range 1.39 to 2.17; WM: 1.19 mL/100 g; interquartile range 0.94 to 1.53; P<0.0001), ADC (GM: 918x10^–6 mm²/s; 868 to 975x10^–6; WM: 805x10^–6; 747 to 870x10^–6; P<0.001), and there was a trend toward a shorter MTT in GM (GM 4.94 s, 4.44 to 5.38; WM 5.15, 4.11 to 5.68; P=0.11).

Conclusions— GM has a higher infarction threshold for CBF, CBV, and ADC than WM in patients within 24 hours of ischemic stroke onset. Hence, when assessing patients for potential therapies, tissue-specific rather than whole-brain thresholds may be a more precise measure of predicting the likelihood of infarction.

Key Words: magnetic resonance imaging, diffusion-weighted • magnetic resonance imaging, perfusion-weighted • stroke, acute • penumbra • white matter

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