Quantitative magnetic resonance imaging in traumatic brain injury

Abstract

Mild traumatic brain injury (TBI) may be complicated by long term cognitive and affective symptoms. Conventional imaging findings often do not correlate with the clinical picture in these patients, and frequently underestimate the extent of damage. Quantitative MR imaging techniques are sensitive to microstructural damage in brain grey matter (GM) and white matter (WM) which appear uninjured on conventional MRI. Previous work has predominantly evaluated their use in acute TBI in moderate and severely injured patients, or in chronic TBI across the severity spectrum. This thesis explored the application of quantitative T1 (qT1) and quantitative T2 (qT2) relaxometry and diffusion tensor imaging (DTI) in the acute evaluation of 44 mild and 9 moderate TBI patients in whom neuropsychological assessment had been performed, and compared the results to those of 30 matched control subjects. By combining the scan data with results from the cognitive testing, this work sought to identify correlations between regions of detectable microstructural damage and the neurocognitive functions related to them. Differences between groups were observed in whole brain normal appearing GM in qT1, and in frontal lobe normal appearing GM and WM in qT1 and DTI measures. Differences were also observed in memory performance and executive function between patients and control subjects which correlated with injury severity. Significant negative correlations were revealed between whole brain WM qT1 time and executive function and negative correlations were shown between frontal and left temporal GM qT1 time and both memory performance and phonemic fluency. Also demonstrated were a positive correlation between frontal GM MD and phonemic fluency, and a negative correlation between frontal GM FA and both memory and executive function. Lastly, increases in WM FA in the corpus callosum, corona radiata, superior longitudinal fasciculus and cingulum were shown to negatively correlate with all components of verbal fluency. This work has demonstrated, using quantitative MR imaging, acute differences at a microstructural level between TBI patients and matched control subjects, in tissue appearing normal on conventional imaging. Furthermore, it has shown that these changes correlate with post-concussive cognitive deficits. It is likely that these changes represent damage as a result of traumatic brain injury in the regions responsible for the cognitive functions found to be impaired.