Combining advanced MR techniques to investigate mild Traumatic Brain Injury and its cognitive consequences

Abstract

Mild Traumatic Brain Injury (TBI) is a major health concern due to its high incidence and lasting cognitive consequences for the patient. Diffuse Axonal Injury (DAI); diffuse damage to axons caused by inertial forces during the TBI, is hypothesised to be a leading cause for these impairments. MRI-based research which has examined mild, acute cases has produced findings which indicate that the mechanisms and progression of mild TBI may be unique and not simply a less pronounced version of severe TBI. This thesis describes a set of experiments which used a variety of advanced MRI techniques to examine the physiological presentation and progression of mild TBI, and how this related to cognitive outcome. Forty-four mild and 9 moderate TBI patients were recruited an average of 6 days post-injury, scanned using a variety MRI techniques and administered a neuropsychological test battery. Twenty-three of these patients (18 mild and 5 moderate) returned one year later and repeated all testing. Thirty-three matched controls were also recruited and given the same set of tests. At the acute time-point patients underperformed on a variety of cognitive tests, although performance at the chronic time-point had normalised compared to controls. The distribution of visible lesions (as identified on quantitative T1 / T2 and T1W scans) was found to be similar to patterns previously reported in severe patients. Results also indicated more lesions to be related to greater acute cognitive deficit. Diffusion Tensor Imaging experimentation revealed a number of unexpected, cognitively-relevant metric changes at the acute and chronic time-points. Magnetic Resonance Spectroscopy investigation also showed a number of unusual metabolite concentration changes and also found these to relate to cognitive functioning. Novel hypotheses were formed from these findings. This work has demonstrated a number of cognitively-relevant physiological changes following TBI which appear unique to mild injury.