Image: Computed tomography is transformed to match surfaces to iSV by pairing tracking system coordinates (Photo courtesy of Dartmouth College).
A novel three-dimensional (3D) optical tracking system provides orthopedic spine surgeons with real-time navigation, like a Google Maps for the body.
Developed by researchers at Dartmouth College (Hanover, NH, USA), the new intraoperative stereovision (iSV) system uses a complex software algorithm and two cameras attached to a surgical microscope in order to produce real-time 3D digitized images for co-registration of the spinal surgical field. The calibrated stereoscopic camera system assists surgeons without any additional radiation or labor-intensive marking of key areas on the patient's spine, providing accurate renderings of where spinal implants, surgical tools, and devices need to go during the procedure.
In a study to define the accuracy of the system, the researchers implanted bone screw fiducials in ten explanted porcine spines, with dorsal soft tissue removed to a variable degree. High-resolution CT scans were then performed. Stereoscopic images were obtained using the iSV, which were then processed, reconstructed, and segmented in a semi-automated manner. Registration of the reconstructed spinal surface with preoperative CT was then performed. Each spine underwent multilevel laminectomy, and target registration error (TRE) was calculated for varying amounts of bone removal.
The results revealed that the overall mean accuracy of iSV registration was 2.21 mm, even when bony anatomy was partially obscured by soft tissues, or if partial midline laminectomy had been performed. The researchers also tested the new iSV system for accuracy and efficiency on pig spines, and are now in the process of converting it into a handheld "wand" that the surgeon can pass over the surgical area. The study was published on March 6, 2018, in Operative Neurosurgery.
“MRIs and CT scans help surgeons identify spine problems, like compressed vertebrae or herniated disks, but finding a clear path to those problem areas is not always as straightforward. Tissue and bone not only stand in the way, they can also move during spinal surgery,” said study co-author professor of biomedical engineering Keith Paulsen, PhD. “Stereovision offers a promising means of registering an open, dorsal spinal surgical field. By rendering images real-time, with a simple handheld tool, we believe we can make surgeries safer and less costly in the future.”
Stereovision is the process of extracting 3D information from multiple 2D views of a scene. It is used in applications such as advanced driver assistance systems (ADAS) and robotic navigation, where it is used to estimate the actual distance or range of objects of interest. The 3D information can be obtained from a pair of images--also known as a stereo pair--by estimating the relative depth of points in the scene. The stereo images are rectified to simplify matching, so that a corresponding point in one image can be found in the other image.