Quantitative Susceptibility Mapping in the Assessment of Single and Repeated Closed Mild Traumatic Brain Injury

Repeated mild traumatic brain injury(mTBI) is one of the important causes of long-term neurological damage in military personnel and athletes. However, it is difficult to make a clear diagnosis of mild traumatic brain injury. This study aimed to analyze the characteristics of changes in magnetic susceptibility values after repeated mTBI by using quantitative susceptibility mapping(QSM). We used QSM, an MRI technique, to scan and image rats with no injury, a single mTBI, and repeated mTBI. The susceptibility maps were calculated using Laplacian, PDF, and iLSQR techniques. The behavior of the rats in each group was analyzed, and brain tissue was extracted for Western blot(WB) and histochemical examination. Both groups of rats showed motor and spatial learning and memory deficits after injury, which persisted for 8 weeks. The changes in magnetic susceptibility in the repeated mTBI group were more significant in the subacute and chronic stages than in the single mTBI group, and no significant differences were detected in the acute stage. Fluorescence staining and WB demonstrated glial proliferation, demyelination, and Tau protein deposition after mTBI, consistent with the changes in magnetic susceptibility. Our study suggests that compared with single mTBI, repetitive mTBI has a compound effect. QSM can detect the changes of magnetic susceptibility in brain tissue after mTBI, and link neurobiochemical changes to MRI data. Therefore, using QSM to detect mTBI-related pathophysiology is credible and feasible.