Stroke onset time using sodium MRI in rat focal cerebral ischemia.
OBJECTIVE
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.
Jones
Stephen C
SC
Department of Anesthesiology, Allegheny-Singer Research Institute, Pittsburgh, PA 15212-4772, USA. sjones@wpahs.org
Kharlamov
Alexander
A
Yanovski
Boris
B
Kim
D Kyle
DK
Easley
Kirk A
KA
Yushmanov
Victor E
VE
Ziolko
Scott K
SK
Boada
Fernando E
FE
D000818:Animals; D002545:Brain Ischemia / Q000139:chemically induced / Q000175:diagnosis* / Q000473:pathology*; D004195:Disease Models, Animal; D007091:Image Processing, Computer-Assisted; D007511:Ischemia / Q000473:pathology; D002546:Ischemic Attack, Transient / Q000473:pathology; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012044:Regression Analysis; D012964:Sodium / Q000737:chemistry; D020521:Stroke / Q000175:diagnosis* / Q000473:pathology*; D013997:Time Factors
D012964:Sodium