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UBC Theses and Dissertations

Novel stand-off pads for ultrasound-CT registration and elastography Kingma, Raoul Jacob


Laparoscopic surgery has many advantages including reduced patient mor- bidity and improved recovery times, but has the drawback of a very limited eld of view. Thus improvements in image guidance in laparoscopic surgery are highly desirable, especially in highly technical operations such as robot- ically assisted laparoscopic partial nephrectomies (RALPN). In RALPN, image guidance can be enhanced by bringing pre-operative computed tomography (CT) and intra-operative ultrasound images into the surgeon's eld of view, depicting underlying anatomy. Multiple tracking and registration steps with inherent trade-o s of accuracy and convenience are normally required to display the images in the camera view. In this thesis, a new tracker-less method is developed for the step of registering pre-operative 3D CT to pre-operative 3D ultrasound which uses a novel ducial stand-o pad. The pad contains ducial markers visible in both modalities which are matched to obtain the registration parameters. The ducial stand-o pad is tested in a controlled phantom study to determine registration accuracy and in a small clinical study to determine clinical feasibility. The ducial stand- o pad is capable of similar registration accuracies to incumbent approaches without the need for external tracking equipment, and is easily integrated into medical imaging protocols. A second enhancement of RALPN image guidance is the integration of ultrasound elastography to display mechanical properties of the tissue. Elas- tography has been in development for over two decades, but further improve- ments are required to improve quantitative estimations of tissue properties. In this thesis, a stand-o pad is used as a method of measuring ultrasound transducer contact force distributions, which will allow force measurements to be used in solving for local tissue elasticities. Forces are obtained by measuring displacements in the stand-o pad and converting them to forces using a nite element model. The accuracy of displacement estimates is tested, and the force computation process is validated. As well, a force measurement system is implemented for use with a three-dimensional linear array transducer. The results show that this is a feasible force measurement method, providing approximately 10% error in force measurements.

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