Cerebrovascular reactivity following focal brain ischemia in the rat: A functional magnetic resonance imaging study

An essential goal of stroke research is to identify potentially salvageable regions of brain that may respond to therapy. However, current imaging met hods are inadequate for this purpose. We therefore used dynamic magnetic re sonance imaging of vascular reactivity following focal occlusion in the rat to determine whether measurement of perfusion reserve would help resolve t his problem. We used the increase in blood-oxygen-level-dependent (BOLD) si gnal that occurs in normal brain following a CO, challenge, to map vascular reactivity over the brain at 30-min intervals for 3.5 h after complete (CO ) or partial (PO) focal ischemia, We assessed the regional correspondence b etween reactivity changes and areas of lowered apparent diffusion coefficie nt (ADC) and initial perfusion deficit. The area of lowered ADC was signifi cantly smaller in the PO group compared to the CO group despite similar are as of perfusion deficit (P < 0.05), We identified four distinct areas withi n hypoperfused brain: a core area with low/absent reactivity and low ADC; b orderzone areas with normal reactivity and either reduced ADC (CO group) or normal ADC (PO group); and an area with normal ADC and reduced/absent reac tivity, In all ischemic regions, the BOLD peak arrival time in the brain wa s delayed or absent. There was a negative correlation between BOLD peak lat ency time and ADC (r = -0.42, P < 0.001), although latency alone did not di fferentiate individual ischemic regions, In conclusion, combining perfusion , ADC, and vascular reactivity mapping of the ischemic brain enables improv ed discrimination of core and borderzone regions. (C) 2001 Academic Press.