Comparison of diffusion, blood oxygenation, and blood volume changes during global ischemia in rats

Rapid diffusion, blood oxygenation, and blood volume weighted echo planar i maging was used to monitor global cerebral ischemia by cardiac arrest in ra ts. Serial CBV measurements used intravascular iron oxide contrast media (i ron dextran), ADC dropped by 5% within 20 sec of cardiac arrest, then conti nued to decay slowly until a larger rapid drop after 2 min. After iron oxid e injection, the initial 5% drop was not observed. The transverse relaxatio n rate (R-2, R-2* no iron injection) increased rapidly after cardiac arrest , peaking at about 30 sec, then declining towards baseline. The CBV dropped by about 50% within 20 sec. The initial 5% ADC drop may be a vascular arti fact. The rapidity of the CBV-weighted signal drop suggests a flow-mediated contribution to the iron oxide contrast mechanism. Magn Reson Med 45:10-16 , 2001. (C) 2001 Wiley-Liss, Inc.