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Towards real-time registration of ultrasound and CT in computer aided orthopaedic surgery applications Brounstein, Anna B Marie


Pelvic fractures are serious injuries that are most commonly caused by motor vehicle accidents and affect people of all ages. Surgeries to realign the pelvis and fix the bone fragments with screws have inherent risks and rely on cumbersome intra-operative radioscopic imaging methods. Ultrasound (US) is emerging as a desirable imaging modality to replace fluoroscopy as an intra-operative tool for pelvic fracture surgery because it is safe, portable and inexpensive. Despite the many advantages of US, it suffers from speckle noise, a limited field of view and a low signal-to-noise ratio. Therefore, we must find a way to efficiently process and utilize ultrasound data so that it can be used to effectively visualize bone. In the past decade, there has been much research focused on fusing US with pre-operative Computed Tomography (CT) to be used in an intra-operative guidance system; however, current methods are either too slow or not robust enough to use in a clinical setting. We propose a method to automatically extract bone features in US and CT volumes and register them using a fast point-based method. We use local phase features to estimate the bone surfaces from B-mode US volumes. We simplify the bone surface using particle simulation, which we optimize using the hierarchical Barnes-Hut algorithm. To ensure the point cloud best represents the bone surface, we reinforce them with high curvature features. We then represent the point clouds using Gaussian Mixture Models (GMMs) and find the correspondence between them by minimizing a measure of distance between the GMMs. We have validated our proposed algorithm on a phantom pelvis and clinical data acquired from pelvic fracture patients. We demonstrate a registration runtime of 1.4 seconds and registration error of 0.769 mm.

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