EVOLUTION OF REGIONAL CHANGES IN APPARENT DIFFUSION-COEFFICIENT DURING FOCAL ISCHEMIA OF RAT-BRAIN - THE RELATIONSHIP OF QUANTITATIVE DIFFUSION NMR IMAGING TO REDUCTION IN CEREBRAL BLOOD-FLOW AND METABOLIC DISTURBANCES

Middle cerebral artery occlusion was per formed in rats while the anim als were inside the nuclear magnetic resonance (NMR) tomograph. Succes sful occlusion was confirmed by the collapse of amplitude on an electr ocorticogram. The ultrafast NMR imaging technique UFLARE was used to m easure the apparent diffusion coefficient (ADC) immediately after the induction of cerebral ischemia. ADC values of normal cortex and caudat e-putamen were 726 +/- 22 x 10(-6) mm(2)/s acid 659 +/- 17 x 10(-6) mm (2)/s, respectively. Within minutes of occlusion, a large territory wi th reduced ADC became visible in the ipsilateral hemisphere. Over the 2 h observation period, this area grew continuously. Quantitative anal ysis of the ADC reduction in this region showed a gradual ADC decrease from the periphery to the core, the lowest ADC value amounting to abo ut 60% of control. Two hours after the onset of occlusion, the regiona l distribution of ATP acid tissue pH were determined with bioluminesce nce and fluorescence techniques, respectively. There was a depletion o f ATP in the core of the ischemic territory (32 +/- 20% of the hemisph ere) and an area of tissue acidosis (57 +/- 19% of the hemisphere) spr eading beyond that of ATP depletion. Regional CBF (rCBF) was measured autoradiographically with the iodo[C-14]antipyrine method, CBF gradual ly decreased from the periphery to the ischemic core, where it decline d to values as low as 5 ml 100 g(-1) min(-1). When reductions in CBF a nd in ADC were matched to the corresponding areas of energy breakdown and of tissue acidosis, the region of energy depletion corresponded to a threshold in rCBF of 18 +/- 14 ml 100 g(-1) min(-1) and to an ADC r eduction to 77 +/- 3% of control. Tissue acidosis corresponded to a fl ow value below 31 +/- 11 ml 100 g(-1) min(-1) and to an ADC value belo w 90 +/- 4% of control. Thus, the quantification of ADC in the ischemi c territory allows the distinction between a core region with total br eakdown of energy metabolism and a corona with normal energy balance b ut severe tissue acidosis.