Optical tracking of a microscope for image-guided intranasal sinus surgery

The objective of this study was to examine the effects of optical and track ing properties on the accuracy of an optically locatable operating microsco pe. The intraoperative arrangement was based on experimental results obtain ed from a skull model, Measurements were taken from 24 patients undergoing intranasal microscopic sinus surgery for various disorders. Two major group s of influencing factors were determined from measurements on the model: 1) optical properties of the microscope, such as the method of focal point ad justment, focal length, and-magnification of the lens; and 2) tracking prop erties of the microscope, such as the distance of the digitizer to the trac ked object, the number of reference infrared light-emitting diodes (IR-LEDs ), and the area circumscribed by these IR-LEDs. Patient measurements showed an overall spatial error of 2.39 +/- 1.15 mm with a laser-supported adjust ment of the focal point of the microscope. Although the associated 95th per centile was at 4.36 mm, such a value is encouraging for further development of microscopically navigable systems. it must be noted that the noninvasiv e patient-to-image registration was performed on the basis of a computed to mographic image with a slice distance of 2 mm.