DETERMINATION OF THE POSITION OF NUCLEUS COCHLEAR IMPLANT ELECTRODES IN THE INNER-EAR

Accurate determination of intracochlear electrode position in patients with cochlear implants could provide a basis for detecting migration of the implant and could aid in the selection of stimulation parameter s for sound processor programming. New computer algorithms for submill imeter resolution and 3-D reconstruction from spiral computed tomograp hic (CT) scans now make it possible to accurately determine the positi on of implanted electrodes within the cochlear canal. The accuracy of these algorithms was tested using an electrode array placed in a phant om model. Measurements of electrode length and interelectrode distance from spiral CT scan reconstructions were in close agreement with thos e stereo microscopy. Although apparent electrode width was increased o n CT scans due to partial volume averaging, a correction factor was de veloped for measurements from conventional radiographs and an expanded CT absorption value scale added to detect the presence of platinum el ectrodes and wires. The length of the cochlear canal was calculated fr om preoperative spiral CT scans for one patient, and the length of ins ertion of the electrode array was calculated from her postoperative sp iral CT scans. The cross-sectional position of electrodes in relation to the outer bony wall and modiolus was measured and plotted as a func tion of distance with the electrode width correction applied.