PET/MRI brain imaging in the acute phase of sports concussion

Objectives: Animal studies have defined a neuropathological cascade following concussion consisting of large and transient changes in the acute phase (hours), followed by longer-lasting sub-acute effects (days). One of the most prominent features is an initial two-fold increase in glucose metabolism, especially in cerebral cortex, that is likely related to restoration of disrupted ion balance across neuronal membranes, followed by a more modest but longer-lasting decrease of unknown origin and clinical significance. In humans, the subacute hypometabolism of glucose and oxygen has been observed to some extent, but the status at the acute phase has not yet been established. The current study uses a novel design to assess regional glucose and oxidative metabolism at the earliest possible time points after injury to establish the existence, magnitude, and regional distribution of this phenomenon - for the first time in the human brain. The long-term objective is to better understand the early pathology of concussion which may lead to improved diagnosis and treatment. Methods We recruited intercollegiate athletes from the football and men’s and women’s lacrosse, soccer, and basketball teams at a single NCAA Division I university. 186 subjects consented to undergo PET/MRI brain imaging in the event that they will sustain a concussion. We implemented a within-subjects (paired) design in which we repeat the imaging protocol when concussion symptoms have completely resolved (>3 months later), as baseline scans on all were impractical. We also recruited a non-injured control group from the same population. A 20 min PET/MRI scan commenced 40 min after i.v. injection of 3-5 mCi of FDG. MRI included standard structural scans and quantitative measures of cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2). The Hammers brain atlas was coregistered onto the PET SUV and MRI images using the structural MRI, and whole brain and regional mean values for both PET and MRI-derived parameters extracted. Clinical data regarding severity of injury and duration of recovery was collected as well. Results Thus far we have completed scans on two concussed subjects within 54 hours of concussion injury and one non-concussed control (follow-up scans of the concussed subjects and imaging of newly concussed subjects in the spring semester are pending). Experienced PET and MRI radiologists found no functional or structural abnormalities.