Intraoperative tracked ultrasound imaging for resolving deformations during spine surgery

Purpose. Conventional image-guided spine surgery relies on surgical trackers for real-time localization of instruments with respect to pre- or intra-operative CT images. These solutions, however, are susceptible to anatomical deformations that may occur due to patient repositioning or imparted changes during surgery. This work presents an approach that uses intraoperative tracked ultrasound (US) imaging to provide real-time verification and recovery of surgical tracking accuracy following spinal deformations. Methods. The approach combines deep-learning segmentation of the posterior vertebral cortices with a multi-step point-to- surface registration that maps reconstructed US features to the 3D CT image. The method was trained on co-registered CT and US images from 5 cadaveric specimens and validated on 2 separate specimens. The geometric accuracy of the registrations was quantified over target regions covering potential pedicle screw entry points. Results. The study confirmed the optimal level for the confidence threshold of the network output and evaluated the minimum required scan length. Vertebrae with simulated displacements were registered with 1.7 ± 0.3 mm of error. The results were robust for up to 50 mm of initial displacement. Conclusions. The solution offers a fast (real-time), portable (small device footprint), and safe (no ionizing radiation) method of tracking anatomical change during surgery. Work currently underway includes implementation of a prototype system for real-time use and evaluation of the surgical workflow with respect to factors including acquisition time, scan extent (number of vertebrae), and scan planes/trajectories.