[ 18 F]FDG-PET Combined with MRI Elucidates the Pathophysiology of Traumatic Brain Injury in Rats.

Non-invasive measurements of brain metabolism using 18 F-fluorodeoxyglucose (FDG) with positron emission tomography (PET) may provide important information about injury severity following traumatic brain injury (TBI). There is growing interest in the potential of combining functional PET imaging with anatomical and functional magnetic resonance imaging (MRI). This study aimed to investigate the effectiveness of combining clinically available FDG-PET with T2 and diffusion MR imaging, with a particular focus on inflammation and the influence of glial alterations after injury. Adult male Sprague Dawley rats underwent a moderate controlled cortical impact (CCI) injury followed by FDG-PET, MRI, and histological evaluation. FDG uptake showed significant alterations in the corpus callosum, hippocampus, and amygdala after TBI, demonstrating that a relatively "focal" CCI injury can result in global alterations. Analysis of MRI T2 intensity and apparent diffusion coefficient (ADC) also showed significant alterations in these regions to include cytotoxic and vasogenic edema. Histology showed increased glial activation in the corpus callosum and hippocampus that was associated with increased FDG uptake at sub-acute time-points. Glial activation was not detected in the amygdala but neuronal damage was evident, as the amygdala was the only region to show a reduction in both FDG uptake and ADC at sub-acute time-points. Overall, FDG-PET detected glial activation but was confounded by the presence of cell damage, whereas MRI consistently detected cell damage but was confounded by glial activation. These results demonstrate that FDG-PET and MRI can be used together to improve our understanding of the complex alterations in the brain after TBI.