京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20803号 / 医博第4303号 / 新制||医||1025(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 平井 豊博, 教授 今中 雄一, 教授 伊達 洋至 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This systematic review aims to investigate the alterations in gray matter volume (GMV) observed in the brains of individuals diagnosed with post-traumatic stress disorder (PTSD) through the Clinical Administered PTSD scale (CAPS) using Voxel-Based Morphometry (VBM) as a method. PTSD is diagnosed when an individual meets all the criteria for PTSD as defined by the DSM, which includes having experienced or witnessed a traumatic event, experiencing intrusive symptoms such as flashbacks or nightmares, avoiding triggers related to the trauma, experiencing negative changes in mood and cognition, and experiencing changes in arousal and reactivity. Previous research investigating gray matter alterations in patients with PTSD has yielded heterogeneous findings. The review incorporates a comprehensive search and analysis of pertinent studies conducted between 1995 and the present. Diverse databases were scrutinized to identify articles that fulfilled the inclusion criteria. Ultimately, a total of seven articles meeting our inclusion criteria were included in this systematic review. The sample sizes ranged from 30 to 75 participants. The control groups in the chosen articles varied, some only had healthy controls (HC), while some had trauma-exposed controls (TC) or included both. The results consistently revealed a reduction in GMV predominantly in the hippocampus, with additional areas exhibiting decreased GMV such as the bilateral hypothalamus and left inferior parietal lobule, right middle temporal gyrus, right inferior temporal gyrus, and right fusiform gyrus, as well as the bilateral calcarine cortex, left dorsal anterior cingulate cortex, left anterior cingulate cortex, and bilateral insula.

Ray tracing is a popular technique used in movies and video games to create compelling visuals. Ray traced computer images are increasingly becoming more realistic and almost indistinguishable from real-word images. Due to the complexity of scenes and the desire for high resolution images, ray tracing can become very expensive in terms of computation and memory. To address these concerns, researchers have examined data structures to efficiently store geometric and material information. Sparse voxel octrees (SVOs) and directed acyclic graphs (DAGs) have proven to be successful geometric data structures for reducing memory requirements. Moxel DAGs connect material properties to these geometric data structures, but experience limitations related to memory, build times, and render times. This thesis examines the efficacy of connecting an alternative material data structure to existing geometric representations. The contributions of this thesis include the creation of a new material representation using hashing to accompany DAGs, a method to calculate surface normals using neighboring voxel data, and a demonstration and validation that DAGs can be used to super sample based on proximity. This thesis also validates the visual acuity from these methods via a user survey comparing different output images. In comparison to the Moxel DAG implementation, this work increases render time, but reduces build times and memory, and improves the visual quality of output images.

Modeling believable lighting is a crucial component of computer graphics applications, including games and modeling programs. Physically accurate lighting is complex and is not currently feasible to compute in real-time situations. Therefore, much research is focused on investigating efficient ways to approximate light behavior within these real-time constraints. In this thesis, we implement a general purpose algorithm for real-time applications to approximate indirect lighting. Based on voxel cone tracing, we use a filtered representation of a scene to efficiently sample ambient light at each point in the scene. We present an approach to scene voxelization using hardware tessellation and compare it with an approach utilizing hardware rasterization. We also investigate possible methods of warped voxelization. Our contributions include a complete and open-source implementation of voxel cone tracing along with both voxelization algorithms. We find similar performance and quality with both voxelization algorithms.

<p>Synthesis of terrains with complex features has been a challenging problem in computer graphics since most of the existing methods are based on the height field representation. Complex features in terrains adds to the overall realism of the terrain. Hence, there is a need to synthesize terrains in real-time with complex features that adhere to user input. The methodology described in this thesis describes a novel way to synthesize terrains with complex features based on user drawn sketches. Layered stack data structure is used to ensure that the resulting terrain has complex features. Since, Neural Networks are used to generate the terrains, the process is real-time.</p>

Susceptibility Weighted Imaging (SWI) utilizes the susceptibility difference between tissues to create a new type of imaging contrast in MRI that is different from conventional spin density, T1-, or T2-weighted imaging. The SWI sequence is a high resolution, fully flow compensated gradient echo sequence. High resolution reduces the signal loss caused by local field inhomogeneities yet with relatively long echo time sufficient contrast can be generated between tissues with a susceptibility difference. Contrast between tissues in the phase image is directly proportional to the susceptibility difference and can be used to enhance the contrast in the magnitude image. In this thesis, we optimize the contrast to noise ratio (CNR) in the magnitude image as a function of the multiplication of the phase mask generated from the phase image. We find that a shorter echo time has the advantage of achieving higher CNR efficiency compared with longer echo times. SWI has found numerous clinical applications due to its sensitivity to blood products. Partial volume effects occur when a voxel contains both venous blood and brain parenchyma. We studied the apparent phase of a voxel as a function of imaging resolution and predict what the best imaging parameters for a specific clinical application should be. Currently, a long acquisition time is the bottleneck for SWI to be used as a routine protocol in the clinical environment. This thesis evaluates segmented echo planar imaging (SEPI) as an alternative to speed up the acquisition while reducing the artifacts usually associated with other fast imaging methods. / Thesis / Doctor of Philosophy (PhD)

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<p dir="ltr">This thesis explores a novel voxel-based 3D modeling tool in virtual reality (VR), assessing its usability with and without Automatic Speech Recognition (ASR). Despite VR's potential for immersive modeling, existing software often lacks functionality or is user-unfriendly. Through participant testing, analysis via the Post-Study System Usability Questionnaire (PSSUQ) and qualitative questions, this study aims to bridge the gap in VR modeling tools, catering to the needs of both laymen and professional modelers.</p>

A key advantage of Additive Manufacturing (AM) is the opportunity to design and fabricate complex structures that cannot be made via traditional means. However, this potential is significantly constrained by the use of a facet-based geometry representation (e.g., the STL and the AMF file formats); which do not contain any volumetric information and often, designing/slicing/printing complex geometries exceeds the computational power available to the designer and the AM system itself. To enable efficient design and fabrication of complex/multi-material complex structures, several algorithms are presented that represent and process solid models as a set of voxels (three-dimensional pixels). Through this, one is able to efficiently realize parts featuring complex geometries and functionally graded materials. This thesis specifically aims to explore applications in three distinct fields namely, (i) Design for AM, (ii) Design for Manufacturing (DFM) education, and (iii) Reverse engineering from imaging data wherein voxel-based representations have proven to be superior to the traditional AM digital workflow. The advantages demonstrated in this study cannot be easily achieved using traditional AM workflows, and hence this work emphasizes the need for development of new voxel based frameworks and systems to fully utilize the capabilities of AM. / MS / Additive Manufacturing(AM) (also referred to as 3D Printing) is a process by which 3D objects are constructed by successively forming one-part cross-section at a time. Typically, the input file format for most AM systems is in the form of surface representation format (most commonly. STL file format). A STL file is a triangular representation of a 3-dimensional surface geometry where the part surface is broken down logically into a series of small triangles (facets). A key advantage of Additive Manufacturing is the opportunity to design and fabricate complex structures that cannot be made easily via traditional manufacturing techniques. However, this potential is significantly constrained by the use of a facet-based (triangular) geometry representation (e.g., the STL file format described above); which does not contain any volumetric (for e.g. material, texture, color etc.) information. Also, often, designing/slicing/printing complex geometries using these file formats can be computationally expensive. To enable more efficient design and fabrication of complex/multi-material structures, several algorithms are presented that represent and process solid models as a set of voxels (three-dimensional pixels). A voxel represents the smallest representable element of volume. For binary voxel model, a value of ‘1’ means that voxel is ‘on’ and value of 0 means voxel is ‘off’. Through this, one is able to efficiently realize parts featuring complex geometries with multiple materials. This thesis specifically aims to explore applications in three distinct fields namely, (i) Design for AM, (ii) Design for Manufacturing (DFM) education, and (iii) Fabricating models (Reverse engineering) directly from imaging data. In the first part of the thesis, a software tool is developed for automated manufacturability analysis of a part that is to be produced by AM. Through a series of simple computations, the tool provides feedback on infeasible features, amount of support material, optimum orientation and manufacturing time for fabricating the part. The results from this tool were successfully validated using a simple case study and comparison with an existing pre-processing AM software. Next, the above developed software tool is implemented for teaching instruction in a sophomore undergraduate classroom to improve students’ understanding of design constraints in Additive Manufacturing. Assessments are conducted to measure students’ understanding of a variety of topics in manufacturability both before and after the study to measure the effectiveness of this approach. The third and final part of this thesis aims to explore fabrication of models directly from medical imaging data (like CT Scan and MRI). A novel framework is proposed which is validated by fabricating three distinct medical models: a mouse skull, a partial human skull and a horse leg directly from corresponding CT Scan data. The advantages demonstrated in this thesis cannot be easily achieved using traditional AM workflows, and hence this work emphasizes the need for development of new voxel based frameworks and systems to fully utilize the capabilities of AM.