Quantitative T2 mapping as a potential marker for the initial assessment of the severity of damage after traumatic brain injury in rat

Severity of traumatic brain injury (TBI) positively correlates with the risk of post-traumatic epilepsy (PTE). Studies on post-traumatic epileptogenesis would greatly benefit from markers that at acute phase would reliably predict the extent and severity of histologic brain damage caused by TBI in individual subjects. Currently in experimental models, severity of TBI is determined by the pressure of applied load that does not directly reflect the extent of inflicted brain injury, mortality within experimental population, or impairment in behavioral tests that are laborious to perform. We aimed to compare MRI markers measured at acute post-injury phase to previously used indicators of injury severity in the ability to predict the extent of histologically determined post-traumatic tissue damage. We used lateral fluid-percussion injury model in rat that is a clinically relevant model of closed head injury in humans, and results in PTE in severe cases. Rats (48 injured, 12 controls) were divided into moderate (mTBI) and severe (sTBI) groups according to impact strength. MRI data (T2, T2*, lesion volume) were acquired 3 days post-injury. Motor deficits were analysed using neuroscore (NS) and beam balance (BB) tests 2 and 3 days post-injury, respectively. Histological evaluation of lesion volume (Fluoro-Jade B) was used as the reference outcome measure, and was performed 2 weeks after TBI. From MRI parameters studied, quantitative T2 values of cortical lesion not only correlated with histologic lesion volume (P<0.001, r=0.6, N=34), as well as NS (P<0.01, r=-0.5, N=34) and BB (P<0.01, r=-0.5, N=34) results, but also successfully differentiated animals with mTBI from those with sTBI 70.6 +/- 6.2 6.2 ms vs. 75.9 +/- 2.6 ms, P<0.001). Quantitative T2 of the lesion early after TBI can serve as an indicator of the severity of post-traumatic cortical damage and neuro-motor impairment, and has a potential as a clinical marker for identification of individuals with elevated risk of PTE.