Diffusion Tensor Magnetic Resonance Imaging (DTI) is a recently-developed technique that can image in vivo the white matter pathways of the central nervous system. This study used 12-direction diffusion-weighted MRI data from nine stroke patients acquired as part of a three-year stroke rehabilitation study coordinated by the Movement Neuroscience Laboratory at the University of Auckland. DTI was used to investigate corticospinal connectivity. From the FA maps, it is found that in those patients whose motor connectivity has been compromised by the stroke to the extent that no motor evoked potential (MEP) can be elicited from a selected affected muscle group, the asymmetry in mean FA values in the posterior limbs of the internal capsules (PLICs) is correlated with functional recovery as measured by the Fugl-Meyer clinical score. Using probabilistic tractography in the contralesional hemisphere produced CST location and somatotopy results that were consistent with those of previous studies. However, in the ipsilesional hemisphere, connectivity results were highly variable. A measure of change in symmetry of mean connectivity is found to correlate with functional recovery as measured by change in FM score. This supports previous work which has correlated CST integrity and functional improvement and it supports the theory that functional recovery after stroke depends on the extent to which motor CNS symmetry can be regained in the new post-stroke architecture. It also suggests that the movement of the fMRI activations occurs in such a way as to make the most of the preserved white matter connectivity.

Thesis (Ph. D. in Biomedical Engineering)--Vanderbilt University, May 2009. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 169-176).

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Additional advisors: Louis B. Nabors, James M. Markert, Donald B. Twieg. Description based on contents viewed July 8, 2009; title from PDF t.p. Includes bibliographical references (p. 73-79).

Thesis (M.S.)--Michigan State University. Dept. of Physics, 2008. / Title from PDF t.p. (viewed on Aug. 7, 2009) Includes bibliographical references (p. 55-57). Also issued in print.

Thesis (Ph. D.)--University of California, San Diego, 2008. / Title from first page of PDF file (viewed November 10, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains viii, 75 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-75).

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17572号 / 工博第3731号 / 新制||工||1569(附属図書館) / 30338 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 小林 哲生, 教授 土居 伸二, 教授 山川 宏 / 学位規則第4条第1項該当

Background. Major depressive disorder (MDD) is a leading cause of death and disability worldwide, and many individuals with MDD will experience treatment-resistant depression (TRD). TRD can lead to the development of suicidal ideation and behaviours, and up to 30% of people with refractory depression will attempt suicide at some point in their life. A neurobiological understanding of suicide is lacking, and neuroimaging markers of illness may elucidate the relationship between suicidal ideation and attempt. Diffusion tensor imaging (DTI) is a particularly sensitive neuroimaging modality that quantifies the microstructural integrity of white matter tracts, which may be useful in the investigation of psychiatric disease. The source of white matter changes may be further elucidated using free water imaging to isolate signal specific to the fibre tract and quantify the fractional volume of the free water compartment. Methodology. For this study, data were obtained from N=36 outpatients with TRD (n=20 suicide ideators and n=16 suicide attempters). Clinical characteristics of the patient sample were examined using clinician-rated and self-report questionnaires of depression and suicidal ideation severity. Whole-brain analysis of DTI data was conducted using tract-based spatial statistics (TBSS) via FMRIB Software Library (FSL) to identify between-group differences in white matter microstructure between suicide ideators and attempters. Free water imaging correction was applied through estimation of a constrained bi-tensor model via an in house MatLab-based script developed at Harvard University. Between-group differences of suicide ideators versus attempters were identified at a family-wise error (FWE) corrected significance threshold of p≤0.05. Subsequent exploratory analyses were performed at an uncorrected significance threshold of p≤0.01. Results. Suicide attempters had greater family history of suicide attempt, higher self-reported suicidal ideation severity, and were more likely to have received overnight treatment in a psychiatric facility in the past. TBSS revealed elevated mean diffusivity (MD), axial diffusivity (AD) and free water (FW) in suicide attempters compared to suicide ideators (thresholded p=<0.05, family-wise error corrected). Subsequent exploratory analyses revealed reduced fractional anisotropy (FA) and elevated radial diffusivity (RD) in fronto-thalamo-limbic white matter tracts of suicide attempters (thresholded p=<0.01, uncorrected). Free water correction appeared to increase detection of fractional anisotropy changes and suppress spurious differences in axial and radial diffusivity. Conclusion. The identification of significantly altered diffusion metrics in suicide attempters compared to suicide ideators suggests white matter pathology in TRD and suicide attempt. The effect of free water correction on diffusion metrics and the elevation of free water itself provide evidence toward the source of anisotropic changes. Future investigations to explore the combined impact of these measures in suicide and depression are recommended.

Atrophy of the corpus callosum (CC) is a documented consequence of moderate-to-severe traumatic brain injury (TBI), which has been expressed as volume loss using quantitative magnetic resonance imaging (MRI). Other advanced imaging modalities such as diffusion tensor imaging (DTI) have also detected white matter microstructural alteration following TBI in the CC. The manner and degree to which macrostructural changes such as volume and microstructural changes develop over time following pediatric TBI and their relation to a measure of processing speed is the focus of this longitudinal investigation. As such, DTI and volumetric changes of the CC in participants with TBI and a comparison group at approximately three and 18 months post injury and their relation to processing speed were determined.