Relation of apparent diffusion coefficient changes and metabolic disturbances after 1 hour of focal cerebral ischemia and at different reperfusion phases in rats

Changes in apparent diffusion coefficients (ADC) were compared with alterat ions of adenosine triphosphate (ATP) concentration and pH in different phas es of transient focal cerebral ischemia to study the ADC threshold for brea kdown of energy metabolism and tissue acidosis during ischemia and reperfus ion. Male Wistar rats underwent 1 hour of middle cerebral artery occlusion without recirculation (n = 3) or with I hour (n = 4) or 10 hours of reperfu sion (n=5) inside the magnet, using a remotely controlled thread occlusion model. ADC maps were calculated from diffusion-weighted images and normaliz ed to the preischemic value to obtain relative ADC maps. Hemispheric lesion volume (HLV) was determined on the last relative ADC maps at different rel ative ADC thresholds and was compared to the HLV measured by ATP depletion and by tissue acidosis. The HLVs, defined by ATP depletion and tissue acido sis, were 26.0% +/- 10.6% and 38.1% +/- 6.5% at the end of ischemia, 3.3% /- 2.4% and 4.8% +/- 3.5% after 1 hour of reperfusion, and 11.2% +/- 4.7% a nd 10.9% +/- 5.2% after 10 hours of recirculation, respectively. The relati ve ADC thresholds for energy failure were consistently approximately 77% of the control value in the three different groups. The threshold for tissue acidosis was higher at the end of ischemia (86% of control) but was similar to the results obtained for ATP depletion after 1 hour (78% of control) an d 10 hours (76% of control) of recirculation. These results indicate that t he described relative ADC threshold of approximately 77% of control provide s a good estimate for the breakdown of energy metabolism not only during mi ddle cerebral artery occlusion but also at the early phase of reperfusion, when recovery of energy metabolism is expected to occur, or some hours late r, when development of secondary energy failure was described.