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UBC Theses and Dissertations

Meshing and rendering of patient-specific deformation models with application to needle insertion simulation Goksel, Orcun


Tissue deformation is common during many medical interventions. An accurate simulation of these procedures necessitates accounting for tissue displacements by modeling tissue deformation and medical tool interaction. In minimally-invasive procedures, due to lack of visibility, physicians rely on haptic feedback and medical imaging to assess the immediate anatomical configuration and relative medical tool position. These procedures are often difficult to learn and therefore extensive training becomes essential. Computerized training systems offer an alternative to cadavers and training on patients. To accurately model the tissue deformation, most such systems require a mesh representation of the anatomy. To replicate the medical imaging feedback offered during procedures, a realistic image simulation approach is also needed. In this thesis, a novel energy-based meshing technique taking medical images and producing desirable meshes for the finite element method is introduced. This method employs an image-based discretization energy combined with a geometry-based element quality energy. The former promotes each mesh element to cover similar intensity image regions, while the latter ensures the element suitability for finite element simulation. A method that can mimic realistic B-mode ultrasound images under deformation is also presented in this thesis. This method first maps the pixels of an image from a deformed mesh configuration back to the nominal configuration, and then interpolates them in a B-mode voxel volume reconstructed a priori. Needle insertion is involved in several medical procedures. These percutaneous procedures will benefit significantly from advances in simulating needle-tissue interaction, for which a 3D model is proposed in this thesis. Simulating needle flexibility is achieved fast and accurately using a novel approach employing torsional springs. The needle insertion simulation with haptic feedback is presented for a training scenario for prostate brachytherapy, where simulated ultrasound images coupled with deformation are also displayed. A scheme to generate patient models for this system is also devised using both the conventional meshing techniques in the literature and the proposed variational meshing method.

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