Does a relative perfusion measure predict cerebral infarct size?

BACKGROUND AND PURPOSE MR perfusion-weighted imaging (PWI) has been extensively used to quantify cerebral perfusion deficits after the onset of focal ischemia. The present study tested whether a relative measure of cerebral blood flow such as is obtained with PWI is sufficient to predict irreversible tissue damage following focal cerebral ischemia and reperfusion in the rat suture model. METHODS In rats, the middle cerebral artery was occluded (MCAO) for 1 hour followed by 1-hour reperfusion. Microspheres labeled with different tracers were injected into the left ventricle to permit measurement of blood flow at different time points: before MCAO, 30 minutes post-MCAO and 30 minutes postreperfusion. Absolute cerebral blood flow (CBF) was determined and relative CBF was calculated by comparing absolute CBF at each time point to baseline values before MCAO (relative CBF(B)) or to corresponding contralateral areas in the noninfarcted hemisphere (relative CBF(C)). Infarct size was assessed by 2,3,5-triphenyltetrazolium chloride staining. RESULTS Absolute CBF in vital tissue was 0.69 +/- 0.07 mL/g/min. In partially and completely necrotic tissue, absolute CBF was 0.39 +/- 0.05 mL/g/min and 0.30 +/- 0.09 mL/g/min, respectively. Although there was a close inverse correlation between infarct volume and absolute CBF (r = 0.79), the correlations between infarct volume and relative CBF(C) were poor (r = 0.21). CONCLUSION The present study revealed that absolute CBF is superior to relative CBF in predicting irreversible tissue damage following ischemia and reperfusion.