Motivation

Each year, over a quarter million spinal fusion surgeries are performed in the United States and more than twenty thousands in Canada. Spinal fusion surgeries are used to treat degenerative disc disease (DDD), spinal stenosis, scoliosis, tumours, vertebral instabilities and fractures. These surgeries require the implantation of pedicle screws in many vertebral segments to help stabilize the vertebrae. However, due to the complexity and variability of the anatomy in the vertebral regions and the incomplete exposure of the vertebral surface, pedicle screw insertion failure rates are as high as 20–30% when using traditional anatomy-guided techniques.

To achieve higher accuracy and reduce the rate of failure, image-guided surgery (IGS) systems are now used to guide many surgeons in spine surgeries. The resulting benefits are numerous, including lower surgical risk, decrease in postoperative complications, more confidence for the surgical procedures and better postoperative functions. A critical step in spine IGS systems is to register patient anatomy to preoperative images. The registration is classically performed manually by identifying anatomical landmarks on both the patient and the preoperative computed tomography (CT) image. However, manual registration is time consuming and invasive. We propose to use intra-operative ultrasound as an imaging tool to collect patient anatomical information during surgery.

The advantages of using intra-operative ultrasound over the current practice of manual registration or fluroscopy based navigation are that the anesthesia time, the risks of infection, and the occupational radiation exposure to surgeons can all be reduced. In addition, if ultrasound images are acquired percutaneously (scanned on the skin), our technique will enable navigation for minimally-invasive surgeries. Ultrasound based spine IGS requires an image registration of intra-operative ultrasound to pre-operative CT images, so that the spatial relationship between the patient spine anatomy and the his/her spine CT images can be obtained. Our current goal is to develop an efficient and robust technique to register vertebral ultrasound to CT to enable the automated and non-invasive registration of patient anatomy to pre-operative CT and surgical plans.