| Description |
For many with severe-to-profound hearing loss, a condition in which the cochlea is unable to convert sound vibration into neural information to the brain, the cochlear implant has become the standard treatment. The goal of a cochlear-implant system is to bypass the malfunctioned cochlea and directly stimulate the nerves responsible for hearing through an array of electrodes on a silicone-elastomer carrier. However, the insertion of the electrode arrays can often cause intracochlear damage and eliminate residual hearing. With increased focus on hearing preservation in cochlear implantation, methods to minimize intracochlear damage have become a priority in electrode-array insertions. This dissertation explores the application of magnetic manipulation toward improved cochlear-implant electrode-array insertions. We start with initial 3-to-1 proof-of-concept experiments to demonstrate the feasibility of this approach. Then, to achieve relevancy at clinical scale, lateral-wall-type electrode-array models, used in the clinic, are slightly modified at the tip to include a tiny magnet. Next, a scala-tympani phantom is designed with both simulated cochleostomy and round-window openings to mimic both classes of insertions typically conducted. In particular, this is the first phantom to model a round-window opening and can be used reliably to simulate insertion forces in cadaver cochleae. Electrode arrays are then magnetically guided through these phantoms with a statistically significant (p < 0.05) reduction in insertion forces, and by as much as 50% for some electrode-array models. In particular, guiding the electrode-array tip through the cochlear hook and the basal turn, in the same insertion, was demonstrated for the first time using this technology. All existing methods to guide the electrode array can only be accomplished for the basal turn. Analysis is conducted to determine the optimal size and placement of a magnetic dipole-field source for use in the clinic. Its placement is determined to be consistently lateral to and anterior to the patient’s cochlea. Its size depends on numerous factors including the patient, torque requirements, and registration error. Sensitivity curves summarizing these factors are provided. The volume of the magnetic dipole-field source can be reduced by a factor of 5, on average, by moving it from the modiolar configuration originally proposed to this optimal configuration. We verify that magnetic forces do not pose any appreciable risk to the basilar membrane at the optimal configuration. Although patient-specific optimal configurations are characterized, a one-size-fits-all version is described that may be more practical and carries the benefit of substantial robustness to registration error. |
