Study on the Image Overlay Approach to AR Navigation System for Transsphenoidal Surgery

In this study, we propose a system for assisting doctors with transsphenoidal surgery by understanding the positions of tumors during surgery. Transsphenoidal surgery requires examining endoscopic images to assess the situation depicted for surgery; determining the positions of tumors and organs is more difficult for transsphenoidal surgeries compared to other more general procedures. Under the proposed system, a three-dimensional (3D) model is created based on the patient’s preoperative MRIs, and a superimposed image is displayed in real time. This system is expected to assist the surgeon in understanding the situation around the operating field.

Markers are used to obtain the data necessary to create an image overlay. The markers are affixed to an operating table and to the end of an endoscope. The patient’s head is held in place during the intraoperative period. The positions of features within the patient’s cranium relative to the operating table marker are obtained through a camera installed on the operating table. The positions of tumors and organs are then estimated from the data obtained and the data from the 3D model created from the patient’s MRIs. The relative position from the marker at the end of the endoscope to the tip of the endoscope is obtained as well, allowing the position of the endoscope tip to be estimated even if the endoscope has been inserted into the body’s interior during the intraoperative period; the tip cannot be seen from the exterior. The relative position of the endoscope tip and the patient’s tumor is calculated, and a 3D model created from the MRI image combined with the current endoscopic image is displayed. The optimum number of simultaneous recognition markers for improving the accuracy of the measurements of the endoscope’s position and orientation was verified, and results of a trial run of the image overlay system conducted using a simplified model were reported.