Relationship Between Electrode-to-Modiolus Distance and Current Levels for Adults With Cochlear Implants

Area of Science:

• Otolaryngology
• Biomedical Engineering
• Neurosurgery

Background:

• Cochlear implant (CI) technology relies on electrical stimulation of the auditory nerve.
• The relationship between electrode proximity to the modiolus and stimulation thresholds has been historically assumed but not formally investigated.
• Understanding this relationship is crucial for optimizing CI programming and patient outcomes.

Purpose of the Study:

• To investigate the correlation between electrode-to-modiolus distance and clinically programmed stimulation levels in cochlear implants.
• To determine if stimulation levels can serve as a proxy for estimating electrode-modiolus geometry.

Main Methods:

• Computed tomography (CT) imaging was used to measure electrode-to-modiolus distance in 137 cochlear-implanted ears across three FDA-approved manufacturers.
• Analysis included 2,365 electrodes, with a focus on precurved arrays.
• Clinical programming data (C/M levels) were converted to charge units for comparison with measured distances.

Main Results:

• Mean modiolar distances were 0.47 mm for perimodiolar electrodes and 1.15 mm for lateral wall electrodes.
• Significant differences in suprathreshold charge values were observed between manufacturers.
• A moderate positive correlation (r = 0.367) was found overall, influenced by manufacturer-specific charge values and array types.
• A weak correlation (r = 0.12) was noted for perimodiolar array electrodes when analyzed separately.

Conclusions:

• Electrode-to-modiolus distance appears to have a minimal contribution to the current required for suprathreshold stimulation in cochlear implants.
• The findings suggest that relying solely on stimulation levels to estimate electrode geometry may be unreliable.
• Further research may be needed to refine CI programming strategies based on individual electrode placement.