Diffusion tensor tractography: Visualization and quantitation with applications to Alzheimer Disease and traumatic brain injury

With the advent of diffusion tensor imaging (DTI) came insight into the organization of the most complex organic computer in existence---the human brain. Diffusion Tensor Tractography (DTT) introduced the ability to visualize, in vivo, axonal fiber bundles, the brain's internal wiring structures.;Rendering tractography in three dimensions aids in the understanding of how the axonal connections of the brain are organized, and is an important tool in illustrating the complex geometry of fiber bundles. To better facilitate the use of 3D visualization for tractography, we wrote flexible custom software targeted at researchers.;The use of tractography need not be limited to visualization; quantitation allows for tractography to be used for clinical applications. In order to create objective metrics of tractography for group analysis, we have created new algorithms to register diffusion data to a single space for comparison, introduced new metrics such as tract count and tract-length histograms to quantify tractography, and developed methods to properly distribute seed points for tractography, a necessary step for quantitation. Finally, we have provided the ability to conduct tractography in the original, and most accurate, acquisition space, and then bring the tracts into a common space for comparison.;Validation of theses metrics and techniques required application to conditions that affect axonal integrity. We examined data from subjects with Alzheimer Disease (AD) and traumatic brain injury (TBI), two afflictions believed to compromise axons of the brain. These studies and others indicate that our understanding of both conditions can be greatly enhanced by the application of DTI and DTT.