Image guided transorbital endoscopic procedures

Abstract

Endoscopic orbital procedures are hindered by both the difficulty in differentiating between orbital structures and the loss of orbital landmarks during these procedures. These difficulties are due to the orbital fat that obstructs direct vision of the orbital structures. Image guidance can address these problems because real time image and physical space tracking information can be provided to the surgeons during the orbital procedure to help in the delivery of therapy to the orbit. Image guidance requires an image-space to physical-space registration and tracking in physical-space with a localizer. To effectively use a magnetic localizer for transorbital guidance, the error metrics must be characterized so that expected guidance errors can be determined. After characterizing the magnetic tracker, the registration of the physical-space to image-space needs to be addressed. Since the target in this research is the optic nerve, a structure which can be anywhere in the retroorbital pyramid, a new form of fiducial placement is created. In this method the retroorbital pyramid was sampled and a fiducial placement which minimized TRE throughout the possible location of the optic nerve head was determined. After characterizing the magnetic localizer and determining an optimal fiducial placement for the task of optic nerve drug delivery, the performance of the system had to be tested. An experimental protocol which allowed performance quantification in an application mimicking manner was developed. Performance metrics from that protocol were gathered on a number of surgeons.