Factors influencing the photogrammetric determination of the processor position in Cochlear Implant treatment

In Cl treatment, the position and location of the processor are a functionally and esthetically relevant aspect for many patients. Especially with bilat. treatment users want a symmetrical arrangement. A method for photogrammetric positioning of the Cl-coil was validated. Digital photos of a head dummy fitted with a CI processor were taken in 7 tests of 10 runs each and the position of the processor relative to the Frankfurt horizontal and the auditory canal was determined photogrammetrically. The parameters zoom, focus, resolution and rotation were varied and the resulting errors in the position of the coil were compared. Under optimal measurement conditions, the inaccuracy in the determination of the coil position was only 0.98+0.54 mm (mean±standard deviation). Greater image distance or slight defocusing had no negative influence on this. An object distance of only 1 m led to a systematic position error of 3.03±0.61 mm (not significant). When the dummy was rotated around the vertical axis, the measured values scattered significantly more with a standard deviation of 1.81 mm more than with all other measurement conditions. The photogrammetric determination of the coil position on a phantom was successfully qualified. The low measurement error of±1-2 mm is within the desired range. For the best possible results, a rotation of the head from the profile plane must be avoided at all costs and a camera distance of 2-3 m must be maintained. On patients, the error will probably be±3-5 mm due to interfering influences (e.g. hair). These results can be used to minimize measurement errors when examining patients by ensuring that the camera is positioned optimally in accordance with the above-mentioned specifications.