Longitudinal MRI studies of brain morphometry

High resolution MR images acquired at multiple time points of the brain allow quantification of localized changes induced by external factors such as maturation, ageing or disease progression/recovery. High-dimensional warping of such MR images incorporates changes induced by external factors into the accompanying deformation field. Deformation fields from high dimensional warping founds tensor based morphometry (TBM), and provides unique opportunities to study human brain morphology and plasticity. In this thesis, specially adapted image processing streams utilizing several image registration techniques to characterize differences between brains, demonstrate the versatility and specificity of the employed voxel-wise morphometric methods. More specifically TBM is used to study neurodegenerative changes following severe traumatic brain injuries. Such injuries progress for months, perhaps even years postinjury. Little information is known about the spatial distribution and the clinical significance of this late atrophy. TBM revealed a large coherent cluster of significant atrophy consisting of the brain stem and cerebellar peduncles extending bilaterally through the thalamus, internal and external capsules, putamen, inferior and superior longitudinal fasciculus, corpus callosum and corona radiata. This indicates that the long-term atrophy is attributable to consequences of traumatic axonal injury. Despite progressive atrophy, remarkable clinical improvement occurred in most patients. The other study utilized TBM and voxel based morphometry (VBM) in two separate papers concerning antipsychotic-naïve first episode schizophrenia. Volume reductions of hippocampal and caudate regions were found in patients compared to controls using VBM. Six months later, TBM revealed continued volume loss in striatum and hippocampus, despite treatment with quetiapine. The mechanisms underlying these progressive brain dynamics, specific antipsychotic compounds and clinical symptoms warrant further clarification.