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L. A. Mawn, N. C. Atuegwu, R. L. Galloway, Jr.; Fiducial Placement for Orbital Endoscopy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4819.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the impact of fiducial placement for accuracy in image guided orbital surgery. We developed a method of orbital endoscopy1 and then married this technique to flexible image guidance.2,3 In this project we compared registration with traditional placement of fiducials to a mathematically optimized periorbital configuration.
A replica of the human skull with a globe and optic nerve within the orbit was created. An endoscope was fitted with a small position and orientation sensor at the tip. An electromagnetic field generator was placed in proximity to the orbital phantom. A mathematical algorithm, simulated annealing, was used to determine optimal fiducial placement. External skin fiducials were placed by both the traditional random method and based on the optimized placement. Preprocedural computed tomographic (CT) images of the phantoms were loaded into both a custom-developed tracking, registration, navigation and rendering software and a commercially available navigation system. The orbital endoscope was then used to reach an optic nerve target with image guidance from the previously acquired CT scan with both fiducial configurations. Target registration error (TRE) was calculated for both the optimized and unoptimized configuration of fiducials.
The CT scan position of the optic nerve within the phantom was accurately determined during the surgical procedure with manageable error. The optimization of fiducial placement reduced the expected TRE by 50% when compared to an unoptimized fiducial placement.
Improved registration results for image guidance were achieved by optimizing fiducial placement. This target registration error minimization method is feasible for in vivo applications. Image guided flexible endoscopy could be advantageous in applying transorbital therapeutics and performing orbital procedures.
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