2D/3D Shape Model Registration with X-ray Images for Patient-Specific Spine Geometry Reconstruction.

The use of preoperative CT and intraoperative fluoroscopic-guided surgical robotic assistance for spinal disease treatment has gained significant attention among surgeons. However, the intraoperative robotic systems lack guidance based on three-dimensional anatomical structures, rendering them unusable when there is a mismatch between preoperative CT and intraoperative fluoroscopy. Additionally, the continuous X-ray imaging during fluoroscopy exposes the patient to significant radiation risks. This paper proposes a 2D/3D registration method to reconstruct 3D patient spine geometry from frontal-view X-ray images. Our aim is to combine this method with intraoperative robotic assistance for spine procedures, enabling three-dimensional spatial navigation for the robotic system and reducing patient radiation exposure. By utilizing 45 frontal-view X-ray images of patients with scoliosis, we trained a 3D trunk anatomy SSM specific to scoliosis. For the registration, a 2D registration-back projection strategy was employed, which first generates the simulated X-ray projection image of the 3D SSM, then non-rigidly registers the projection image with the patient X-ray image, and finally back-project the 2D registration into 3D to guide the shape deformation of the 3D SSM. This approach was evaluated using X-ray images of 10 scoliosis patients. The results demonstrate the ability to reconstruct the anatomical structure and curvature of the spine in X-ray images. The registration accuracy of the SSM was assessed by visualizing the alignment between the registered model and X-ray images, as well as calculating the average distance between the vertebral disc center points of the model and expert-annotated anatomical landmarks in the patient’s X-rays. The average distance between the registered model’s vertebral disc centers and the patient’s X-ray anatomical positions was 11.38 mm. The registered model exhibited a high degree of alignment with the curvature of the spine in X-ray images.