Localization and assessment of subcortical white matter pathways with diffusion tensor magnetic resonance imaging

Improved techniques for studying the human brain are necessary for advancing our understanding of brain structure, function, and development. For this dissertation project, I developed magnetic resonance imaging (MRI) tools for studying the brain's white matter and then clinically applied these tools. Diffusion tensor MRI (DTI) is a non-invasive technique that uses the Brownian motion of water to probe the brain's structure and organization. DTI fiber tracking uses the observed pattern of water diffusion to infer axonal connectivity and delineate white matter pathways in three dimensions. This bioengineering thesis project involved acquiring DTI data, implementing a DTI fiber tracking algorithm, performing feasibility and validity studies, performing patient studies, and transitioning DTI fiber tracking into a routinely used surgical planning tool.; A bootstrap based model of the uncertainty in the primary eigenvector's orientation was implemented. Understanding the primary eigenvector's measurement error is important for assessing the accuracy of DTI fiber tracking.; Software tools were developed for generating DTI fiber tracks and making tract-specific measurements. These analysis tools were used in a study of patients with congenital hemiplegia. It was determined that DTI fiber tracking could be used to quantitatively detect structural differences in motor tracts affected by hemiplegia.; Intraoperative cortical and subcortical motor stimulation sites were used to validate the spatial distribution of DTI fiber tracks. These studies showed that DTI fiber tracking could accurately follow the motor tract between functional cortex and the cerebral peduncle in brain tumor patients. Based on these findings, a presurgical DTI fiber tracking protocol was developed and used routinely for surgical planning.; The tools and results from this dissertation were used in a clinical study of white matter development. DTI fiber tracking was performed on premature infants undergoing early phases of white matter maturation. Age related changes in DTI parameters were observed in both the sensory and motor tracts. DTI parameters within different regions of the sensorimotor white matter pathways were observed to be heterogeneous.