CA also plays an important role in intraoperative assistance. Representative examples of CA in intraoperative assistance, or surgical navigation are provided in this section.
Tracking of the positions and the orientations of an endoscope and a forceps is vital during interventions. There are two methods for tracking an endoscopic camera: (a) sensor-based tracking and (b) image-based tracking. A positional tracker is mostly used in surgical navigation because it is quite robust. Image-based tracking uses preoperative and intraoperative images to track an endoscope.
An optical or electromagnetic tracking system is typically utilized in surgical navigation (Fig. 4.17). These positional tracking systems give position and orientation in their coordinate system S. To generate a virtual laparoscopic view corresponding to a current real endoscopic view from preoperative CT images, it is necessary to obtain the transformation matrix representing the relationship between two coordinate systems C(s) and C(c), where C(s) and C(c) show the coordinate systems of the sensor and the preoperative coordinate systems, respectively. When the position of known
Fig. 4.17 Laparoscopic surgery navigation using an optical positional sensor (Courtesy by Dr. Yuichiro Hayashi)
- 4 Applied Technologies and Systems
points p; in C(s) and C(c) is measured, the transformation matrix between the two coordinates are obtained by solving the following equation:
where p(s) and p(c) are locations of ;th known point, which are measured on CT images and on the patient. Anatomical landmarks or fiducial landmarks attached to a patient’s body are utilized. To obtain T, we need three points if we consider only rotation and translation. If we obtain T*, we transform an endoscope position or a forceps position by T* and generate a surgical assistance image.