Geodesic tractography segmentation for directional medical image analysis

Acknowledgements page removed per author's request, 01/06/2014.Geodesic Tractography Segmentation is the two component approach presented in this thesis for the analysis of imagery in oriented domains, with emphasis on the application to diffusion-weighted magnetic resonance imagery (DW-MRI). The computeraided analysis of DW-MRI data presents a new set of problems and opportunities for the application of mathematical and computer vision techniques. The goal is to develop a set of tools that enable clinicians to better understand DW-MRI data and ultimately shed new light on biological processes. This thesis presents a few techniques and tools which may be used to automatically find and segment major neural fiber bundles from DW-MRI data. For each technique, we provide a brief overview of the advantages and limitations of our approach relative to other available approaches.Ph.D.Committee Chair: Tannenbaum, Allen; Committee Member: Barnes, Christopher F.; Committee Member: Niethammer, Marc; Committee Member: Shamma, Jeff; Committee Member: Vela, Patrici

Neuroinflammation and white matter alterations in obesity assessed by Diffusion Basis Spectrum Imaging

Human obesity is associated with low-grade chronic systemic inflammation, alterations in brain structure and function, and cognitive impairment. Rodent models of obesity show that high-calorie diets cause brain inflammation (neuroinflammation) in multiple regions, including the hippocampus, and impairments in hippocampal-dependent memory tasks. To determine if similar effects exist in humans with obesity, we applied Diffusion Basis Spectrum Imaging (DBSI) to evaluate neuroinflammation and axonal integrity. We examined diffusion-weighted magnetic resonance imaging (MRI) data in two independent cohorts of obese and non-obese individuals (Cohort 1: 25 obese/21 non-obese; Cohort 2: 18 obese/41 non-obese). We applied Tract-based Spatial Statistics (TBSS) to allow whole-brain white matter (WM) analyses and compare DBSI-derived isotropic and anisotropic diffusion measures between the obese and non-obese groups. In both cohorts, the obese group had significantly greater DBSI-derived restricted fraction (DBSI-RF; an indicator of neuroinflammation-related cellularity), and significantly lower DBSI-derived fiber fraction (DBSI-FF; an indicator of apparent axonal density) in several WM tracts (all correcte

Subclinical Metabolic and Cardiovascular Factors and Brain White Matter Microstructural Integrity in Young Women

Pregnancy places women in a state of metabolic change that can exacerbate underlying risk factors for disease. Prior studies note physiological risk factors for pregnancy-induced hypertensive disorders, but few have focused on whether these cardiovascular and metabolic risk factors affect brain structure in early adulthood prior to pregnancy. Therefore, more research is needed to assess how subclinical cardiovascular and metabolic risk factors may affect brain health or be exacerbated by the hormonal and metabolic imbalances caused by pregnancy. This study examined how specific cardiovascular and metabolic risk factors assessed prior to pregnancy affected brain white matter microstructural integrity. This study examined 62 participants, all young (mean age 31 years), healthy women, who received both metabolic and cardiovascular assessments as well as multi-modality MRI imaging including acquisition of T2 Fluid-Attenuated Inversion Recovery (FLAIR) sequencing and Diffusion Tensor Imaging (DTI). The hypotheses were that abnormal cardiovascular and metabolic profiles would be associated with increased white matter hyperintensities (WMH), and abnormal cardiovascular and metabolic findings would be related to lower Fractional Anisotropy (FA) and increased Mean Diffusivity (MD) in posterior cortical areas. The results showed that the presence of WMH was related to increased MD in bilateral white matter tracts and altered measures of cardiac function. FA and MD in numerous posterior and occipital tracts, commissural fibers and subcortical structures correlated with age, BMI, and measures of cardiovascular and metabolic function such as pulse wave velocity (PWV), cholesterol and insulin resistance (HOMA-IR). These relationships shed light on women’s cerebrovascular health as it relates to subclinical risk factors at a young age, prior to pregnancy. More research must be done to examine how subclinical risk factors may impact potentially dangerous pregnancy outcomes in the form of hypertensive disorders such as pre-eclampsia and how these early life influences on brain structure impact brain functioning in late age

Fiber consistency measures on brain tracts from digital streamline, stochastic and global tractography

La tractografía es el proceso que se emplea para estimar la estructura de las fibras nerviosas del interior del cerebro in vivo a partir de datos de Resonancia Magnética (MR). Existen varios métodos de tractografía, que generalmente se dividen en locales y globales. Los primeros intentan reconstruir cada fibra por separado, mientras que los segundos intentan reconstruir todas las estructuras neuronales a la vez, buscando una configuración que mejor se ajusta a los datos proporcionados. Dichos métodos globales han demostrado ser más precisos y fiables que los métodos de tractografía local, para datos sintéticos. Sin embargo hasta la fecha no hay estudios que definan la relación entre los parámetros de adquisición de la MR y los resultados de tractografía estocástica o global con datos reales. Esta tésis de Master pretende mostrar la influencia de ciertos parámetros de adquisición como el factor de difusión de las secuencias de adquisición, el espaciado entre voxels o el número de gradientes en la variabilidad de las tractografías obtenidas.Teoría de la Señal, Comunicaciones e Ingeniería TelemáticaMáster en Investigación en Tecnologías de la Información y las Comunicacione

Genetic risk for increased oxidative stress in the aging brain:Implications for white matter integrity and cognition

Oxidative stress is a key mechanism of the aging process that can cause damage to brain white matter and cognitive functions. Allele variations of two polymorphisms (SOD2, CAT -262) have been associated with abnormalities in antioxidant enzyme activity, suggesting a risk for enhanced oxidative damage to brain white matter and cognition among older individuals with these genetic mutations. The present study utilized diffusion tensor imaging (DTI) and neuropsychological assessment to compare differences in microstructural white matter integrity and cognitive performance among 96 older adults (age 50-85) with and without genetic risk factors of SOD2 (rs4880) and CAT -262 (rs1001179). Results revealed significantly higher radial diffusivity (RD) in the anterior thalamic radiation (ATR) among CC genotypes of SOD2 compared to CT/TT genotypes. Further, the CC genotype significantly moderated the relationship between the hippocampal segment of the cingulum (CHC) and processing speed. Neither CAT-262, nor the combined effect of SOD2 and CAT-262 risk alleles were significantly associated with brain outcomes in this cohort. Collectively these results suggest that the CC genotype of SOD2 is an important genetic marker of suboptimal brain aging in this cohort of otherwise healthy older adults