Diffusion and high resolution MRI of traumatic brain injury in rats: Time course and correlation with histology

Although widely employed in studies of cerebral ischemia, the use of diffus ion-weighted imaging (DWI) for traumatic brain injury (TBI) has been both l imited and primarily confined to the first few hours after injury. Therefor e, the present study examined the temporal evolution of magnetic resonance imaging (MRI) signal changes from hours to weeks after moderate fluid-percu ssion TBI in rats. We used isotropic diffusion along three directions and h igh resolution (HR) spin-echo pulse sequences to visualize DWI and HR MRI c hanges, respectively. Late changes were compared to histopathological and n eurological outcome. A significant decrease (P < 0.05) in the apparent diff usion coefficients (ADC) below preinjury levels was found in the left corte x and left hippocampus (ipsilateral to injury) at 1-2 h post-TBI. At 2 week s post-TBI, ADCs were significantly elevated (P < 0.05) above preinjury lev els in both carter and hippocampus. Regions of hypo- and hyperintensity det ected in HR MRI scans also showed evidence of tissue damage by histological evaluation. Neurological assessment indicated that such changes were obser ved at a level of injury which produced moderate impairment 2 weeks after t he insult. These results indicate that alterations in DWI and HR MRI signal s occur both early (hours) and late (weeks) after lateral fluid-percussion injury. Furthermore, the study showed that DWI was sensitive to MR signal c hange at 1-2 h post TBI (in select ROIs), whereas HR scans showed MR signal change primarily at later time points (3-4 h and later). Moreover, regions which demonstrate late changes are associated with histological damage and neurological impairment. The study demonstrates the utility of MRI to dete ct early changes, in some cases, that are predictive of long lasting damage verified histologically. (C) 2000 Academic Press.