Ischemic thresholds for gray and white matter: a diffusion and perfusion magnetic resonance study.
OBJECTIVE
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.
Arakawa
Shuji
S
National Stroke Research Institute, Heidelberg Heights, Victoria, 3084, Australia.
Wright
Peter M
PM
Koga
Masatoshi
M
Phan
Thanh G
TG
Reutens
David C
DC
Lim
Indra
I
Gunawan
Marveyles R
MR
Ma
Henry
H
Perera
Nilupul
N
Ly
John
J
Zavala
Jorge
J
Fitt
Gregory
G
Donnan
Geoffery A
GA
D000368:Aged; D000369:Aged, 80 and over; D001783:Blood Flow Velocity; D001921:Brain / Q000473:pathology / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011859:Radiography; D020521:Stroke / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013997:Time Factors