Registration of preoperative CT to intraoperative ultrasound via a statistical wrist model for scaphoid fracture fixation


Scaphoid fracture is the most probable outcome of wrist injury and it often occurs due to sudden fall on an outstretched arm. To fix an acute non-displaced fracture, a volar percutaneous surgical procedure is highly recommended as it provides faster healing and better biomechanical outcome to the recovered wrist. Conventionally, this surgical procedure is performed under X-ray based fluoroscopic guidance, where surgeons need to mentally determine a trajectory of the drilling path based on a series of 2D projection images. In addition to challenges associated with mapping 2D information to a 3D space, the process involves exposure to ionizing radiation. Ultrasound (US) has been suggested as an alternate; US has many advantages including its non-ionizing nature and real-time 3D acquisition capability. US images are, however, difficult to interpret as they are often corrupted by significant amounts of noise or artifact, in addition, the appearance of the bone surfaces in an US image contains only a limited view of the true surfaces. In this thesis, I propose techniques to enable ultrasound guidance in scaphoid fracture fixation by augmenting intraoperative US images with preoperative computed tomography (CT) images via a statistical anatomical model of the wrist. One of the major contributions is the development of a multi-object statistical wrist shape+scale+pose model from a group of subjects at wide range of wrist positions. The developed model is then used to register with the preoperative CT to obtain the shapes and sizes of the wrist bones. The intraoperative procedure starts with a novel US bone enhancement technique that takes advantage of an adaptive wavelet filter bank to accurately highlight the bone responses in US. The improved bone enhancement in turn enables a registration of the statistical pose model to intraoperative US to estimate the optimal scaphoid screw axis for guiding the surgical procedure. In addition to this sequential registration technique, I propose a joint registration technique that allows a simultaneous fusion of the US and CT data for an improved registration output. We conduct a cadaver experiment to determine the accuracy of the registration process, and compare the results with the ground truth.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

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