IMPROVED AND SIMPLIFIED METHODS FOR SPECIFYING POSITIONS OF THE ELECTRODE BANDS OF A COCHLEAR IMPLANT ARRAY

Objective: To develop techniques for measuring the positions of the in dividual electrodes of a multiple channel cochlear implant and for est imating associated characteristic frequencies. Background: Information concerning the positions of the individual electrodes of a cochlear i mplant array is important for analyzing speech perception or psychophy sical data and for optimizing speech-processing strategies. This study presents two techniques for obtaining such information from postopera tive plain film radiographs. Methods: A template spiral shape, derived from analysis of the radiographs of 30 cochlear implant patients, is used to obtain measurements of the angular positions of the electrode bands within scala tympani. A research technique measures angular posi tions and estimates characteristic frequencies for all electrode bands but requires that the positions of two cochlear landmarks and all ele ctrode bands be digitized. A clinical technique provides similar angle and frequency estimates but requires a minimum of information to be e xtracted visually from the radiograph. The lateral positions of the ba nds are estimated, in the research technique, using mean outer and inn er wall functions obtained from 11 Silastic molds of scala tympani. Re sults: The mean position of the implanted array relative to the mean s cala tympani outer wall function was consistent with published histolo gic observations of implanted temporal bones. Measured angles did not vary greatly with experimenter or with rotation of the cochlea relativ e to the radiographic beam by up to 20 degrees. Conclusions: The techn iques described allow, principally, measurement of the longitudinal po sitions of the bands of a cochlear implant in scala tympani and estima tion of corresponding characteristic frequencies.