REGIONAL ASSESSMENT OF TISSUE OXYGENATION AND THE TEMPORAL EVOLUTION OF HEMODYNAMIC PARAMETERS AND WATER DIFFUSION DURING ACUTE FOCAL ISCHEMIA IN RAT-BRAIN

We assessed the temporal and spatial correlation between perfusion def icits and tissue damage in the first hours of focal cerebral ischemia in the rat. Repetitive dynamic susceptibility contrast-enhanced ('bolu s track') and diffusion-weighted (DW) MRI, performed from ca. 0.5 up t o 6 h after intraluminal middle cerebral artery occlusion (MCA-O), all owed the determination of the time course of various hemodynamic param eters and ischemic tissue damage in specific brain regions. In additio n, blood oxygenation level dependent (BOLD) MRI combined with a respir atory challenge provided complementary information on brain hemodynami cs. Within the territory of reduced blood now, the degree of the hemod ynamic disturbances was heterogeneous. Interestingly, the spatial patt ern of perfusion deficiencies remained essentially the same from ca. 0 .5 to 6 h post-MCA-O. However, the area and the extent of ischemic tis sue damage, as expressed by reductions in the apparent diffusion coeff icient (ADC) of tissue water, tended to progress with increasing occlu sion time. Different ADC profiles correlated with different degrees of hemodynamic disturbances. In the ischemic core, which showed severely compromized perfusion, the ADC dropped significantly within 1 h. In p erifocal areas, ADC reductions were delayed and less pronounced. Data from the bolus track and BOLD MRI experiments revealed the existence o f residual flow, particularly in perifocal regions. Our data point to a time-dependent change in the relationship between ADC reductions and hemodynamic alterations and, therefore, agree with the concept of a p rogressively increasing perfusion threshold for ischemic tissue damage as a function of time of ischemia.