Optimizing the Magnetic Dipole-Field Source for Magnetically Guided Cochlear-Implant Electrode-Array Insertions

Abstract

Magnetic guidance of cochlear-implant electrode arrays during insertion has been demonstrated in vitro to reduce insertion forces, which is believed to be correlated to a reduction in trauma. In those prior studies, the magnetic dipole-field source (MDS) was configured to travel on a path that would be coincident with the cochlea’s modiolar axis, which was an unnecessary constraint that was useful to demonstrate feasibility. In this paper, we determine the optimal configuration (size and location) of a spherical-permanent-magnet MDS needed to accomplish guided insertions with a 100 mT field strength required at the cochlea, and we provide a methodology to perform such an optimization more generally. Based on computed-tomography scans of 30 human subjects, the MDS should be lateral-to and slightly anterior-to the cochlea with an approximate radius (mean and standard deviation across subjects) of 64 mm and 4.5 mm, respectively. We compare these results to the modiolar configuration and find that the volume of the MDS can be reduced by a factor of five with a 43% reduction in its radius by moving it to the optimal location. We conservatively estimate that the magnetic forces generated by the optimal configuration are two orders of magnitude below the threshold needed to puncture the basilar membrane. Although subject-specific optimal configurations are computed in this paper, a one-size-fits-all version with a radius of approximately 75 mm is more robust to registration error and likely more practical. Finally, we explain how to translate the results obtained to an electromagnetic MDS.

A three-dimensional thermal model of the human cochlea for magnetic cochlear implant surgery

“…Magnet size is described in Figure 10 by its characteristic length, defined as the ratio of the magnet volume to its surface area L c = Vmagnet Amagnet . In this paper, four magnet sizes are considered based on reported sizes used in magnetic insertion of cochlear implant EAs [2,39,3,40]. All magnets are assumed to be cylindrical.…”

Translational and Rotational Arrow Cues (TRAC) Navigation Method for Manual Alignment Tasks

“…Many image-guided surgery (IGS) tasks require a clinician to manually position an instrument in space, with respect to a patient, with five or six degrees of freedom (DOF), comprising a 3-DOF position and a 2-DOF or 3-DOF orientation. For example, in our group, we are interested in positioning robotic [4] and magnetic [14] devices in the proper location with respect to a patient's head, based on preoperative CT scans, during robot-assisted cochlear implant surgery. Displaying the current and desired pose of the object on a 2D display (e.g., a computer monitor) is straightforward.…”

Thermal Model of an Omnimagnet for Performance Assessment and Temperature Control

“…An Omnimagnet [1] is a relatively new electromagnetic device that enables remote magnetic manipulation [2] of devices such as medical implants and microrobots. We are particularly interested in its use for robotically assisted insertion of cochlear-implant electrode arrays [3,4,5], in which an Omnimagnet is adjacent to the patient's head during surgery. An Omnimagnet is comprised of three orthogonal nested solenoids with a spherical ferromagnetic core at the center, and is optimized to generate a dipole-like magnetic field in any direction.…”