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

Rapid diffusion, blood oxygenation, and blood volume weighted echo planar imaging was used to monitor global cerebral ischemia by cardiac arrest in rats. Serial CBV measurements used intravascular iron oxide contrast media (iron dextran). ADC dropped by 5% within 20 sec of cardiac arrest, then continued to decay slowly until a larger rapid drop after 2 min. After iron oxide injection, the initial 5% drop was not observed. The transverse relaxation 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 artifact. 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.