Lt. Cohen et al., IMPROVED AND SIMPLIFIED METHODS FOR SPECIFYING POSITIONS OF THE ELECTRODE BANDS OF A COCHLEAR IMPLANT ARRAY, The American journal of otology, 17(6), 1996, pp. 859-865
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.