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Endovascular interventions are a type of minimally invasive surgery used to diagnose and treat vascular conditions. Long, thin and flexible medical devices like catheters are percutaneously inserted into the blood vessels. Time-action analysis has shown that the navigation of the medical devices from the access to the destination site is inefficient, thereby increasing the inherent risks and costs of endovascular interventions. A new steerable catheter with two deflectable segments may benefit the procedure by reducing the number of device exchanges while speeding up the process. The new catheter is designed for navigation to the arteries in the legs. Currently, multiple selective catheters are used consuctively to first cross the aortic bifurcation and then navigate down the leg. The new steerable catheter is designed to three commonly used selective catheters. A handle is also designed to actuate the two deflectable segments. A prototype is built and experimentally evaluated. The catheter has the required axial and rotational stiffness, but lacks the required bending elasticity. The deflectable segments can successfully be actuated into the desired geometries. However, the bending elasticity must be improved before conclusive evidence can be found that the catheter can replace the selected conventional catheters. Experiments within a vascular model show promising initial results.

At Mechatronics in Medicine (MiM) Laboratory of Imperial College London, a neurosurgical steerable flexible probe ( STING) that is used to access deep brain lesions through curved trajectories is currently being developed. The focus of my research project is mainly on trajectory planning of the flexible probe i.e. investigation on how to increase efficiency and performance of the trajectory planning. Some experiments have been thoroughly done to measure the performance of a well known sampling based path planning method, Reachability-Guided Rapidly-exploring Random Tree (RG-RRT). The first step to improve the performance was to migrate from MATLAB to Python-C++ which yielded 12-13 times performance speedup. Besides taking a close look at the software implementation details, the second step was to improve the algorithm by implementing a waypoint cache and exploiting some parallelization techniques. The parallelization techniques cover multi-core CPU (OR parallel, AND parallel, OR+AND parallel and Manager-Worker) and GPGPU techniques. At the end of my research project, RG-RRT with waypoint cache was experimentally able to reach 4 times performance speedup, while parallelization on multi-core CPU with AND parallel technique has shown the most significant result by obtaining approximately 5 times performance speedup. The other parallelization, which was done through the use of an NVIDIA CUDA-enabled GPU, has successfully obtained 10 times performance speedup. Despite its higher rate of performance speedup, later it was shown that GPGPU technique suffers the most from inefficiency due to I/O bottleneck that is caused by device-host memory transfer.

This thesis explores the possibilities of design optimization techniques for designing shape memory alloy structures. Shape memory alloys are materials which, after deformation, can recover their initial shape when heated. This effect can be used for actuation. Emerging applications for shape memory alloys are e.g. miniaturized medical instruments with embedded actuation, as well as microsystem components. However, designing effective shape memory alloy structures is a challenging task, due to the complex material behavior and the close relationship between geometry, electrical, thermal and mechanical properties of the structure. In this thesis, various approaches are developed to combine optimization algorithms with computational modeling of shape memory alloy structures. The focus is on the shape memory behavior of NiTi alloys that exhibit the R-phase/austenite transformation. Dedicated computationally efficient constitutive models are formulated to capture this behavior and predict the performance of designs. The considered optimization approaches include deterministic shape optimization, shape optimization under bounded-but-unknown uncertainty, gradient-based shape optimization and topology optimization. Together they provide a collection of efficient and systematic techniques to generate well-performing designs. Their applicability and effectiveness is evaluated by application to design studies of realistic complexity, involving the design of miniature grippers and steerable catheters. The developed design optimization techniques are expected to be of great use for the design of future instruments and devices that utilize shape memory alloy actuation.

Objective The integrated visualization of cardiac MRI during a ventricular tachycardia (VT) mapping and ablation procedure would provide improved catheter guidance and tissue assessment. We developed a system for and explored the added value of simultan o s visualization of intracardiac voltage measurements and MRI-derived myocardial scar information during VT ablation procedures. Method We propose the use of a synchronized 3D and 2D view. In 3D, the catheter will be guided optimally by assessing 3D scar characteristics and its relation to the ventricular anatomy. In 2D, a detailed assessment of the tissue can be made. We developed several 3D visualization techniques, including volume rendering of the scar and myocardial surfaces colored according to the voltage measurements. We also visualized context structures in the heart. For the 2D view, we proposed showing three adjacent slices simultaneously. To link the 3D with the 2D view, we added a linking plane and linking contours; the slice level shown in the 2D view is indicated in the 3D view. Results We evaluated our method via a case study during which we simulated the visual environment of an ablation procedure. The MRI-based volume rendering of scar tissue and the linking between the 3D and 2D views were both positively received. However, the visualization of the voltage measurements was found to be hard to interpret, partly due to the perceptually suitable but non-standard colormap. Conclusions Based on this study, we can conclude that our approach of displaying MRI data and integrating it with voltage measurements has potential to improve VT ablation procedures.

This article illustrates the opportunities that combining computational modeling and systematic design optimization techniques offer to facilitate the design process of shape memory alloy (SMA) structures. Focus is on shape memory behavior due to the R-phase transformation in Ni-Ti, for which a dedicated constitutive model is formulated. In this paper, efficient topology and shape optimization procedures for the design of SMA devices are described. In order to achieve fast convergence to optimized designs, sensitivity information is computed to allow the use of gradient-based optimization algorithms. The effectiveness of the various optimization procedures is illustrated by numerical examples, including the design of a miniature SMA gripper and a steerable SMA active catheter. It is shown that design optimization enables designers of SMA structures to systematically enhance the performance of SMA devices for a variety of applications.