Trackerless 3D Ultrasound Stitching for Computer-Assisted Orthopaedic Surgery and Pelvic Fractures

In pelvic fracture surgeries, percutaneous screws must be placed accurately for effective fixation and to prevent damage to surrounding tissue structures (Bates 2010). Fluoroscopy is currently used to image the pelvis to provide guidance, but this produces harmful ionizing radiation and does not allow three-dimensional (3D) visualisation (Gay 1992). Ultrasound offers three-dimensional, non-ionizing, real-time, and inexpensive imaging. It has thus emerged as an alternative to fluoroscopy for intraoperative imaging in computer-assisted orthopaedic surgery (CAOS). However, ultrasound-based surgical guidance is challenging because ultrasound produces inherently noisy images with limited field-of-view. While several techniques have been proposed to improve bone clarity in ultrasound scans (Hacihaliloglu 2009; Quader 2014), there is limited work on enhancing ultrasound’s field-of-view for CAOS. In particular, improving the field-of-view for surgical guidance for pelvic fracture surgeries would be needed to achieve accurate and reliable registration to preoperative data, and accurate screw placement in the pelvis (Keil 2009). In this work, we propose and evaluate the feasibility of a trackerless method for stitching volumetric ultrasound to achieve an extended field-of-view. Previous ultrasound stitching methods have used optical tracking to determine the spatial alignment between volumes (Dalvi 2010; Ni 2009), but these approaches require additional hardware. Our method contributes towards simpler surgical navigation as it does not require tracking equipment.