How can intraoperative 3D CT assist surgical robots to complete surgical navigation?

 Surgical robots have high requirements for intraoperative alignment, and it is not enough to rely only on their own navigation and localization functions, which need to be combined with intraoperative 3D CT images to improve the accuracy of navigation.

Unlike spiral CT in the radiology scanning room, intraoperative 3D CT uses cone-beam CT scanning equipment, commonly known as 3D C-arm and O-arm.
How does intraoperative 3D CT assist the surgical robot to accomplish surgical navigation? The following is an example of intraoperative 3D mobile C-arm (PLX C7600) assisted spine surgery to introduce the four processes in the surgical process.

(I) Intraoperative image acquisition
Intraoperative navigation can use CT images or MRI images. In orthopedic surgery, the precision of bony anatomical structures is required to be higher, so the application of intraoperative CT images is more widely used than intraoperative MRI, and the use of mobile intraoperative CT is more popular.
Fluoroscopy-based navigation is similar to CT-based navigation in that multiple intraoperative fluoroscopic images can be uploaded to the workstation for 3D reconstruction. The latest fluoroscopy-based navigation techniques allow real-time reconstruction based on preoperative CT data, thus displaying the true anatomy of the patient intraoperatively.
(Ⅱ) Motion Capture
Surgical navigation requires a motion capture system to track the movement of surgical instruments in space and synchronize the changes in the movement position of surgical instruments on the screen. At present, the commonly used motion capture system for spine surgery navigation is mostly optical tracking technology.
Optical motion capture systems mainly rely on optical cameras to accurately measure the spatial position of an object through triangulation. In order to ensure the accuracy of real-time surgical navigation, the optical camera should be avoided as much as possible during the surgical operation.
Surgical navigation with the help of motion capture system can track the position of surgical instruments in space as well as the trajectory in real time, and can recognize the translation and rotation of surgical instruments in the coordinate system in real time.
(Ⅲ) Image Alignment
Before the start of surgery, the surgical navigation system needs to correlate the anatomical structure of the intraoperative captured images with the actual anatomical structure of the patient, which in turn helps the surgeon to perform image-guided surgery. Image alignment is the process of aligning and integrating the coordinate system of the captured images with the navigation tracking system to provide a “map” for surgical navigation.
Taking the Perlove spine surgery navigation system as an example, it automatically completes the image coordinate establishment and system coordinate alignment by tracking the three-dimensional acquisition trajectory of the C-arm in a way that is not affected by the quality of the image. Compared with scale alignment, the accuracy of trajectory alignment is higher, with fewer operation steps and high system operation efficiency.

(Ⅳ) Image visualization
Once the image alignment is complete, the surgical navigation system displays the virtual images of the surgical instruments overlaid with the 3D images acquired intraoperatively. As the surgeon moves the real surgical instruments, their corresponding virtual images can also be synchronized and moved in real time on the 3D CT image.
By looking at the surgical navigation system’s screen, the surgeon is able to visualize in real time the relative position of the instruments to the anatomical structures of the patient’s surgical site. This information is critical to help the surgeon accurately assess the distance of the surgical instruments from the target surgical site, so that he or she can accurately perform the surgical operation along the pre-planned surgical path.