Flow-sensitive alternating inversion recovery (FAIR) is a noninvasive method for perfusion imaging. It has been shown that the FAIR signal may depend on hemodynamic parameters other than perfusion, the most important one being transit delays of labeled spins to the observed tissue. These parameters are expected to change with ischemia. The goal of this study was to assess the effect of these changes on the interpretation of FAIR results in the case of altered perfusion. This was investigated in a rat model of transient cerebral ischemia. It was shown that the ratio of FAIR signal in the infarct compared to the contralateral side was lower at short inflow times, which suggests that transit times affected the effective FAIR signal. The FAIR results were compared with those from functional histology and dynamic susceptibility contrast MRI, and the findings indicated that the altered kinetics of the FAIR signal were related to reduced and delayed inflow in the infarct region--not to a decrease in the number of functional vessels.
Copyright 2004 Wiley-Liss, Inc.