Real-time intracochlear imaging of automated cochlear implant insertions in whole decalcified cadaver cochleas using ultrasound

Objectives: This study aimed to determine the feasibility of combining high-frequency ultrasound imaging, automated insertion, and force sensing to yield more information about cochlear implant insertion dynamics. Methods: An apparatus was developed combining these aspects along with software to control implant and imaging probe positions. Decalcified unfixed human cochleas were implanted at various speeds, insertion sites, and implant models while imaging near the implant tip throughout insertion and recording force data from the cochlea mounting stage. Ultrasound video data were also captured. Results: The basilarmembrane (BM)was frequently penetrated by the implant in either the mid-basal or lower middle turn. Measurements were also performed of apical BM motion in response to upstream implant movement at varying insertion speeds. Increasing insertion speed resulted in greater BM displacement. Discussion: Multiple insertions per cochlea increase the volume of data per specimen while also reducing variability due to differences between cochleas. However, to image inside the cochlea with ultrasound, the bone had to be decalcified, which likely had a significant effect upon the response of tissue to contact by the implant. As calcified bone strongly reflects ultrasound, we also found ultrasound imaging to be an excellent method for easily assessing bone decalcification progress. Conclusion: This technique may be very useful for some studies, although the confounding effects of bone decalcification may make results of other studies too difficult to generalize. The approach could be adapted to other real-time imaging modalities, such as optical coherence tomography.