CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT App. Ser. No. PCT/US2017/033757, filed May 22, 2017.

BACKGROUND

1. Field

The present disclosure relates generally to the implantable portion of implantable cochlear stimulation (or “ICS”) systems.

2. Description of the Related Art

ICS systems are used to help the profoundly deaf perceive a sensation of sound by directly exciting the intact auditory nerve with controlled impulses of electrical current. Ambient sound pressure waves are picked up by an externally worn microphone and converted to electrical signals. The electrical signals, in turn, are processed by a sound processor, converted to a pulse sequence having varying pulse widths, rates and/or amplitudes, and transmitted to an implanted receiver circuit of the ICS system. The implanted receiver circuit is connected to an implantable electrode array that has been inserted into the cochlea of the inner ear, and electrical stimulation current is applied to varying electrode combinations to create a perception of sound. The electrode array may, alternatively, be directly inserted into the cochlear nerve without residing in the cochlea. A representative ICS system is disclosed in U.S. Pat. No. 5,824,022, which is entitled “Cochlear Stimulation System Employing Behind-The-Ear Sound processor With Remote Control” and incorporated herein by reference in its entirety. Examples of commercially available ICS sound processors include, but are not limited to, the Harmony™ BTE sound processor, the Naida™ CI Q Series sound processor and the Neptune™ body worn sound processor, which are available from Advanced Bionics.

As alluded to above, some ICS systems include an implantable cochlear stimulator (or “cochlear implant”), a sound processor unit (e.g., a body worn processor or behind-the-ear processor), and a microphone that is part of, or is in communication with, the sound processor unit. The cochlear implant communicates with the sound processor unit and, some ICS systems include a headpiece that is in communication with both the sound processor unit and the cochlear implant. The headpiece communicates with the cochlear implant by way of a transmitter (e.g., an antenna) on the headpiece and a receiver (e.g., an antenna) on the implant. Optimum communication is achieved when the transmitter and the receiver are aligned with one another. To that end, the headpiece and the cochlear implant may include respective positioning magnets that are attracted to one another, and that maintain the position of the headpiece transmitter over the implant receiver. The implant magnet may, for example, be located within a pocket in the cochlear implant housing. To that end, the headpiece and the cochlear implant may include respective positioning magnets that are attracted to one another, and that maintain the position of the headpiece transmitter over the implant receiver. The implant magnet may, for example, be located within a pocket in the cochlear implant housing. The skin and subcutaneous tissue that separates the headpiece magnet and implant magnet is sometimes referred to as the “skin flap,” which is frequently 3 mm to 10 mm thick.

The magnitude of the retention force between the headpiece magnet and implant magnet is an important aspect of an ICS system. If the force is too low, the headpiece will not remain in place on the head during typical activities. If, on the other hand, the force is too high, the pressure on the skin flap can result is discomfort and tissue necrosis. The magnitude of the retention force is dictated by the strength of the magnets and the distance between the magnets, which is a function of the thickness of the skin flap. The strength of the headpiece magnet is frequently selected during the post-implantation headpiece fitting processes.

One example of a conventional cochlear implant (or “implantable cochlear stimulator”) is the cochlear implant10illustrated inFIGS. 1 and 2. The cochlear implant10includes a flexible housing12formed from a silicone elastomer or other suitable material (e.g., with a hardness from 50 to 70 Shore A), a processor assembly14, a cochlear lead16with a flexible body18and an electrode array20, and an antenna22that may be used to receive data and power by way of an external antenna that is associated with, for example, a sound processor unit. The antenna22is located within an antenna portion24of the housing12. A cylindrical positioning magnet26, with north and south magnetic dipoles that are aligned in the axial direction of the disk, is located within the housing magnet pocket28. The positioning magnet26is used to maintain the position of a headpiece transmitter over the antenna22.

Some conventional cochlear implants are not compatible with magnetic resonance imaging (“MRI”) systems. As illustrated inFIG. 3, the implant positioning magnet26produces a magnetic field M in a direction that is perpendicular to the patient's skin and parallel to the central axis A. This magnetic field direction is not aligned with, and may be perpendicular to (as shown), the direction of the MRI magnetic field B when the patient is within the MRI system. The misalignment of the interacting magnetic fields M and B is problematic for a number of reasons. The dominant MRI magnetic field B (typically 1.5 Tesla or more) may generate a significant amount of torque T on the implant magnet26. The torque T may be sufficient to deform the housing12and cause reorientation of the implant magnet. Reorientation of the magnet26can place significant stress on the dermis (or “skin”), which cause significant pain. In some instances, the implant magnet26may rotate 180 degrees, thereby reversing the N—S orientation of the magnet.

One proposed solution to the problems associated with MRI magnetic fields is to provide cochlear implants with a magnet aperture that allows the magnet to be removed from the cochlear implant, and then reinserted into the cochlear implant, in situ, i.e., with the cochlear implant accessed by way of an incision in the skin. The present inventors haves determined that removal and reinsertion can be problematic because some patients will have many MRI procedures during their lifetimes, and repeated surgeries can result in skin necrosis at the implant site.

More recently, magnet apparatus that are compatible with MRI systems have been developed for use in cochlear implants. Various examples of an MRI-compatible magnet apparatus are disclosed in WO2016/190886 and WO2016/191429, which are incorporated herein by reference in their entireties. The magnet apparatus30illustrated inFIGS. 4 and 5, which may be incorporated into the cochlear implant10in place of the magnet26, includes a case32, with base34and a cover36, and magnetic material particles (or “particles”)38within the internal volume of the case32.

The particles38are independently and freely rotatable and otherwise movable relative to one another and to the case32, and are free to move from one X-Y-Z coordinate to another and/or rotate in any direction. For example, some particles38may move linearly and/or rotate relative to other particles and relative to the case32, while the orientation of the case remains the same, when the magnet apparatus30is exposed to an external magnetic field. Although not limited to any particular shape, the magnetic material particles38may be spherical or may be non-spherical, polyhedral shapes or at least substantially polyhedral shapes, i.e., multi-sided shapes that are regular or irregular, symmetric or asymmetric, with or without smooth side surfaces, and with or without straight edges, that will permit the particles to rotate relative to one another when loosely packed. Any three-dimensional shapes that permit the movement described above may also be employed. The magnetic material particles38may be formed from materials that include, but are not limited to, neodymium-iron-boron (“Nd2Fe14B”) magnetic material, isotropic neodymium, anisotropic neodymium, samarium-cobalt (“Sm2Co17”). An external magnetic field may be used to reorient the magnetic material particles38within the case32such that the N—S orientations of the particles are the same (i.e., the particles are “aligned”). For example, the magnet apparatus30may be positioned adjacent to a magnet (e.g., a rare-earth magnet) that creates a magnetic field of 1.5 Tesla or more to reorient the magnetic material particles38. This alignment establishes the desired N—S orientation of the magnet apparatuses30(e.g., parallel to the central axis A). Such reorientation may be performed before or after the magnet apparatus30is incorporated into a cochlear implant and prior to the implant being implanted into the patient.

Although magnetic material particle-based MRI-compatible magnet apparatus are an advance in the art, the present inventors have determined that the magnetic material particles may become misaligned (i.e., no longer aligned with one another and/or in their desired N—S orientation) subsequent to being exposed to a relatively strong MRI magnetic field B (e.g., 3.0 Tesla or more). The misalignment reduces the attraction strength of the magnet apparatus and, accordingly, impairs the ability of the magnet apparatus to maintain the position of a headpiece transmitter over the cochlear implant antenna.

SUMMARY

A particle alignment method in accordance with at least one of the present inventions includes the step of positioning a cochlear implant, which is implanted within a patient's head and which includes a magnet apparatus with a central axis and magnetic material particles, at a location outside of the scanning area of an MRI system, adjacent to the MRI system, and within the MRI magnetic field in such a manner that the central axis of the magnet apparatus is at least substantially parallel to the MRI magnetic field.

A particle alignment indication kit in accordance with at least one of the present inventions includes a location identification template including a template magnet and at least one aperture and an alignment gauge including a gauge magnet and an at least substantially transparent member associated with the gauge magnet.

A method in accordance with at least one of the present inventions includes the steps of, prior to an MRI procedure where the patient is placed into a scanning area of an MRI system that includes an MRI magnet that creates an MRI magnetic field, placing a location identification template on the patient's head and over the magnet apparatus of an implanted cochlear implant and making at least one mark on the patient's head based on the position of the location identification template, removing the location identification template from the patient's head after the at least one mark has been made and prior to the MRI procedure, and after the MRI procedure, placing an alignment gauge on the patient's head and over the magnet apparatus and determining whether or not the magnetic material particles of the magnet apparatus are in the pre-MRI orientation by observing the position of the at least one mark on the patient's head relative to the alignment gauge.

There are a number of advantages associated with such apparatus and methods. By way of example, but not limitation, at least some of the present inventions may be used to determine whether or not the magnetic material particles in an MRI-compatible magnet apparatus are in their desired N—S orientation. At least some of the present inventions may be used to return magnetic material particles in an MRI-compatible magnet apparatus to their desired N—S orientation after an MRI procedure has been performed.

The above described and many other features of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

