Patent Publication Number: US-2021170167-A1

Title: Cochlear implants and magnets for use with same

Description:
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 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 Advanced Bionics™ Harmony™ BTE sound processor, the Advanced Bionics™ Naida™ BTE sound processor and the Advanced Bionics™ Neptune™ body worn sound processor. 
     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. 
     One example of a conventional cochlear implant (or “implantable cochlear stimulator”) is the cochlear implant  10  illustrated in  FIGS. 1 and 2 . The cochlear implant  10  includes a flexible housing  12  formed from a silicone elastomer or other suitable material, a processor assembly  14 , a cochlear lead  16  with a flexible body  18  and an electrode array  20 , and an antenna  22  that may be used to receive data and power by way of an external antenna that is associated with, for example, a sound processor unit. A cylindrical positioning magnet  24 , with north and south magnetic dipoles that are aligned in the axial direction of the disk, is located within the housing  12 . The magnet  24  is used to maintain the position of a headpiece transmitter over the antenna  22 . 
     It is sometimes necessary to remove the magnet from the cochlear implant, and then reinsert the magnet, in situ, i.e., with the cochlear implant accessed by way of an incision in the skin. To that end, the positioning magnet  24  is carried within an internal magnet pocket  26  and can be inserted into, and removed from, the housing pocket by way of a magnet aperture  28  that extends through the housing top wall  30 . The magnet  22  is larger than the magnet aperture  28 , i.e., the outer perimeter of the magnet is greater than the perimeter of the magnet aperture. The portion of the top wall  30  between the aperture  28  and the outer edge  32  of the magnet  24  forms a retainer  34  that, absent deformation of the aperture and retainer, prevents the magnet from coming out of the housing  12 . The volume V 1  of the ring of housing material that forms the retainer  34  (which is the same flexible material that forms the remainder of the housing  12 ) is shown with cross-hatching in the cross-section illustrated in  FIG. 2A . During installation and removal, the aperture  28  and retainer  34  are stretched or otherwise deformed so that the magnet  24  can pass through the aperture  28 . 
     The present inventors have determined that conventional cochlear implants are susceptible to improvement. For example, some conventional cochlear implants may not be compatible with magnetic resonance imaging (“MRI”) systems. As illustrated in  FIG. 3 , the implant magnet  24  produces a magnetic field M in a direction that is perpendicular to the patient&#39;s skin and parallel to the 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. 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 magnet  24 . The torque T may be sufficient to deform the retainer  34  and dislodge the implant magnet  24  from the pocket  26  by way of the aperture  28  and/or reverse the magnet. In particular, the present inventors have determined that the volume V 1  of flexible housing material that forms the retainer  34  can be insufficient to resist the torque T on the implant magnet  24 . 
     One proposed solution involves surgically removing the implant magnet  24  prior to an MRI procedure and then surgically replacing the implant magnet thereafter. The present inventors have determined that a solution which allows an MRI procedure to be performed without magnet removal/replacement surgery, but which also permits magnet removal/replacement if otherwise necessary, would be desirable. 
     SUMMARY 
     A cochlear implant in accordance with one of the present inventions includes a cochlear lead, a housing including a magnet pocket and a magnet aperture, a magnet, located within the magnet pocket, having a top surface adjacent to the magnet aperture that defines a top magnet outer perimeter and a bottom surface adjacent to the bottom wall that defines a bottom magnet outer perimeter that is greater than the top magnet outer perimeter, an antenna within the housing, a stimulation processor within the housing. The present inventions also include systems with such a cochlear implant in combination with a headpiece. 
     A cochlear implant in accordance with one of the present inventions includes a cochlear lead, a flexible housing formed from a first flexible material having a first hardness and including a magnet pocket and a magnet aperture, a magnet with a side surface within the magnet pocket, a flexible buttress located within the flexible housing and adjacent to the side surface of the magnet, the flexible buttress being formed from a second flexible material having a second hardness that is greater than the first hardness, an antenna within the housing, a stimulation processor within the housing. The present inventions also include systems with such a cochlear implant in combination with a headpiece. 
     There are a number of advantages associated with such apparatus. For example, the torque applied to the implant magnet by a strong magnetic field, such as an MRI magnetic field, will not dislodge the implant magnet from the within the housing and/or reverse the magnet. As a result, surgical removal of the cochlear implant magnet prior to an MRI procedure, and then surgical replacement thereafter, is not required. In those instances where removal is required, the present cochlear implants need not preclude such removal and replacement. Additionally, the present cochlear implants prevent the implant magnet from being dislodged and/or reversed without increasing the thickness and volume of the implant or substantially increasing the rigidity of the implant. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Detailed descriptions of the exemplary embodiments will be made with reference to the accompanying drawings. 
         FIG. 1  is a plan view of a conventional cochlear implant. 
         FIG. 2  is a section view taken along line  2 - 2  in  FIG. 1 . 
         FIG. 2A  is an enlarged view of a portion of  FIG. 2 . 
         FIG. 3  is a side view showing a conventional cochlear implant in an MRI magnetic field. 
         FIG. 4  is a plan view of a cochlear implant in accordance with one embodiment of a present invention. 
         FIG. 5  is a section view taken along line  5 - 5  in  FIG. 4 . 
         FIG. 5A  is an enlarged view of a portion of  FIG. 5 . 
         FIG. 6  is a perspective view of a magnet in accordance with one embodiment of a present invention. 
         FIG. 7  is a side view of the magnet illustrated in  FIG. 6 . 
         FIG. 8  is the section view illustrated in  FIG. 5  with the magnet removed. 
         FIG. 9  is a section view of a cochlear implant in accordance with one embodiment of a present invention. 
         FIG. 9A  is an enlarged view of a portion of  FIG. 9 . 
         FIG. 10  is a section view of a flexible magnet buttress in accordance with one embodiment of a present invention. 
         FIG. 11  is a perspective view of the flexible magnet buttress illustrated in  FIG. 10 . 
         FIG. 12  is a block diagram of a cochlear implant system in accordance with one embodiment of a present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The following is a detailed description of the best presently known modes of carrying out the inventions. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the inventions. 
     One example of a cochlear implant (or “implantable cochlear stimulator”) in accordance with the present inventions is the cochlear implant  100  illustrated in  FIGS. 4-8 . Referring first to  FIG. 4 , the exemplary cochlear implant  100  includes a resilient flexible housing  102  formed from a silicone elastomer or other suitable material, a processor assembly  104 , a cochlear lead  106 , and an antenna  108  that 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 cochlear lead  106  may include a flexible body  110 , an electrode array  112  at one end of the flexible body  102 , and a plurality of wires (not shown) that extend through the flexible body from the electrodes  114  (e.g., platinum electrodes) in the array  112  to the other end of the flexible body. The exemplary antenna  108  is a coil antenna with one or more loops (or “turns”), and three loops are shown in the illustrated embodiment. The exemplary processor assembly  104 , which is connected to the electrode array  112  and antenna  108 , includes a printed circuit board  116  with a stimulation processor  118  that is located within a hermetically sealed case  120 . The stimulation processor  118  converts stimulation data into stimulation signals that stimulate the electrodes  114  of the electrode array  112 . The hermetically sealed case  120  is located within a processor portion  122  of the housing  102 . A positioning magnet  124  is located within an antenna portion  126  of the housing  102 . The magnet  124 , which is used to maintain the position of a headpiece transmitter over the antenna  108 , is centered relative to the antenna  108 . 
     Turning to  FIG. 5 , the exemplary housing antenna portion  126  includes a magnet pocket  128  which is surrounded by a bottom wall  130  that is located under the magnet pocket (in the illustrated orientation), a top wall  132  that is located above the magnet pocket (in the illustrated orientation) and a side wall  134  that is lateral of, and extends around, the magnet pocket. During use, the housing bottom wall  130  faces the patient&#39;s skull and the outer surface of the bottom wall defines a portion of the bottom surface of the cochlear implant  100 , which is the surface of the cochlear implant that faces the patient&#39;s skull. The magnet  124  can be inserted into, and removed from, the magnet pocket  128  by way of a magnet aperture  136  that extends through the housing top wall  132 . The magnet  124  is larger than the magnet aperture  136  and portions of the top wall  132  and side wall  134  between the magnet aperture  136  and the side surface of the magnet  124  form a retainer  138 . 
     As the strength of a conventional retainer (e.g., retainer  34  in  FIG. 2 ) may be insufficient to prevent a conventional magnet from being dislodged during an MRI procedure, the present implant housing  102  and magnet  124  are configured so as to increase the volume of material that defines the retainer  138 , as compared to the conventional retainer in an otherwise identical cochlear implant, without increasing the thickness and volume of the implant. To that end, and referring to  FIGS. 6-8 , the exemplary magnet  124  has a top surface  140 , a bottom surface  142 , and a side surface  144  between the top and bottom surfaces. The perimeter P MT  of the top surface  140  is less than the perimeter P MB  of the bottom surface  142 . In the illustrated implementation, the magnet  124  has a frustoconical shape and, accordingly, the top and bottom surface perimeters P MT  and P MB  are circular and the diameter D MT  of the top surface  140  is less than the diameter D MB  of the bottom surface  142 . The top and bottom corners (or “edges”)  146  and  148  of the exemplary magnet  124  are rounded such that the cross-section is substantially trapezoidal (i.e., trapezoidal but for the rounded corners). The rounded edges ease insertion and removal of the magnet  124  to and from the pocket  128 . The exemplary magnet pocket  128  ( FIG. 8 ), which is similarly shaped, has a top surface  150 , a bottom surface  152 , a side surface  154  between the top and bottom surfaces, and rounded top and bottom corners  156  and  158 . Here too, the perimeter of the top surface  150  is less than the perimeter of the bottom surface  152  and, in the illustrated implementation, the magnet pocket  128  has a frustoconical shape. The top and bottom surface perimeters of the magnet pocket  128  are, therefore, circular and the diameter D PT  of the pocket top surface  150  is less than the diameter D PB  of the bottom surface  122 . 
     Turing to  FIG. 5A , and as compared to the retainer  34 , an additional volume ΔV of material is added to the volume V 1  to form the volume V 2  that defines the retainer  138 . The material in the volume V 2 , which is the same flexible material that forms the remainder of the housing  102 , is shown with both cross-hatching (volume V 1 ) and gray (volume ΔV) in the cross-section illustrated in  FIG. 5A . In the illustrated implementation, the respective configurations of the magnet  124  and the housing pocket  128  results in a retainer material volumetric increase of about 45%, as compared to an otherwise identical implant with a cylindrical magnet in a cylindrical pocket (e.g., the magnet  24  in pocket  26 ) having a diameter equal to the bottom surface diameter of the magnet  124 , without increasing the volume or thickness of the implant. The torque generated by an MRI magnetic field will not dislodge the magnet  124  from the housing  102  and/or reverse the magnet within the housing in the manner described above with reference to  FIGS. 1-3 . Nevertheless, if necessary, the flexibility of the housing material allows the magnet  124  may be removed and replaced in situ. One example of a tool that may be used to remove the magnet  124 , and then replace the magnet, is disclosed in PCT Pub. No. WO2014/164023. 
     Although the present inventions are not so limited, the exemplary magnet  124  includes a magnetic element  160  ( FIGS. 5 and 5A ) or magnetic object of some other shape formed from a ferromagnetic material and a thin hermetically sealed housing  162  formed from, for example, biocompatible metals and/or plastics. Such housing materials may, in some instances, be non-magnetic or paramagnetic. Suitable materials include, but are not limited to, titanium or titanium alloys, polyether ether ketone (PEEK), low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polyamide. In particular, exemplary metals include commercially pure titanium (e.g., Grade 2) and the titanium alloy Ti-6Al-4V (Grade 5). With respect to size and shape, and although the present inventions are not so limited, in some implementations, the bottom magnet diameter D MB  may range from 9 mm to 16 mm, the top magnet diameter D MT  may range from 6 mm to 12 mm, and the thickness may range from 1.5 mm to 3.5 mm. The bottom magnet diameter D MB  of the exemplary magnet  124  is 13.0 mm, the top magnet diameter D MT  is 10.5 mm, and the thickness is 2.2 mm, in the illustrated embodiment. It should be noted, however, that magnet size is a function of the strength of the ferromagnetic material and, as stronger materials become available, the size may be reduced. The dimensions of the magnet pocket  128  may be equal to those of the magnet  124 . 
     Another exemplary cochlear implant is generally represented by reference numeral  100  in  FIGS. 9 and 9A . Cochlear implant  100   a  is substantially similar to cochlear implant  100  and similar elements are represented by similar reference numerals. Here, however, a portion of the material that forms the retainer is harder than the material that forms the remainder of the housing, thereby increasing the strength of the retainer. By way of example, but not limitation, the exemplary housing  102   a  includes antenna portion  126   a  with a buttress  164  that is adjacent to (and in some instances is in contact with) the magnet side wall  144 . The buttress  164  is formed from flexible material that is harder than the material that forms the remainder of the housing  102   a . The buttress  164  forms part of the retainer  138   a  and, as a result, the retainer  138   a  is stiffer than the retainer  138 . Turning to  FIGS. 10 and 11 , the buttress  164  includes a generally annular body  166  with an inner surface  168  having a size and shape that corresponds to the size and shape of the magnet side wall  144 . The perimeter P BT  and diameter D BT  at the top of the inner surface  168  are equal to (or are close to equal to) the perimeter P MT  and the diameter D MT  of the magnet top  140 , and the perimeter P BB  and diameter D BB  of the bottom of the inner surface  168  are equal to (or are close to equal to) the perimeter P MB  and the diameter D MB  of the magnet bottom  144 . The buttress annular body  166  also has outer surface  170  as well as an opening  172  that is adjacent to the magnet aperture  136  and through which the magnet  124  can pass when a tool is used to remove and/or replace the magnet in the manner described in, for example, PCT Pub. No. WO2014/164023. 
     The volume of the buttress  164  may be larger than the volume ΔV created by the configurations of the magnet  124  and magnet pocket  128  (which is shown in gray in  FIG. 9A ), may be the same as the volume ΔV, or may be less than the volume ΔV. In the illustrated implementation, the volume of the buttress  164  is greater than the volume ΔV, and the additional buttress volume further strengthens the area around the magnet pocket  128 . With respect to materials, the buttress  164  may be formed from a silicone elastomer or other suitable flexible material that is harder than the material that forms the remainder of the housing, yet still allows the housing  102   a  to conform to the skull and the magnet to be removed if necessary. In some instances, the buttress material may be from 27% to 63% harder than the housing material. For example, the buttress material may have a hardness that ranges from 70 to 90 Shore A, while the housing material may have a hardness that ranges from 55 to 70 Shore A. The buttress  164  may, for example, be a separately molded structure onto which the remainder of the housing  102   a  is overmolded. 
     As illustrated in  FIG. 12 , the exemplary cochlear implant system  50  includes the cochlear implant  100  (or  100   a ), a sound processor, such as the illustrated body worn sound processor  200  or a behind-the-ear sound processor, and a headpiece  300 . 
     The exemplary body worn sound processor  200  in the exemplary ICS system  50  includes a housing  202  in which and/or on which various components are supported. Such components may include, but are not limited to, sound processor circuitry  204 , a headpiece port  206 , an auxiliary device port  208  for an auxiliary device such as a mobile phone or a music player, a control panel  210 , one or microphones  212 , and a power supply receptacle  214  for a removable battery or other removable power supply  216  (e.g., rechargeable and disposable batteries or other electrochemical cells). The sound processor circuitry  204  converts electrical signals from the microphone  212  into stimulation data. The exemplary headpiece  300  includes a housing  302  and various components, e.g., a RF connector  304 , a microphone  306 , an antenna (or other transmitter)  308  and a positioning magnet apparatus  310 , that are carried by the housing. The magnet apparatus  310  may consist of a single magnet or may consist of one or more magnets and a shim. The headpiece  300  may be connected to the sound processor headpiece port  206  by a cable  312 . The positioning magnet apparatus  310  is attracted to the magnet  124  of the cochlear stimulator  100 , thereby aligning the antenna  308  with the antenna  108 . The stimulation data and, in many instances power, is supplied to the headpiece  300 . The headpiece  300  transcutaneously transmits the stimulation data, and in many instances power, to the cochlear implant  100  by way of a wireless link between the antennas. The stimulation processor  118  converts the stimulation data into stimulation signals that stimulate the electrodes  114  of the electrode array  112 . 
     In at least some implementations, the cable  312  will be configured for forward telemetry and power signals at 49 MHz and back telemetry signals at 10.7 MHz. It should be noted that, in other implementations, communication between a sound processor and a headpiece and/or auxiliary device may be accomplished through wireless communication techniques. Additionally, given the presence of the microphone(s)  212  on the sound processor  200 , the microphone  306  may be also be omitted in some instances. The functionality of the sound processor  200  and headpiece  300  may also be combined into a single head wearable sound processor. Examples of head wearable sound processors are illustrated and described in U.S. Pat. Nos. 8,811,643 and 8,983,102, which are incorporated herein by reference in their entirety. 
     Although the inventions disclosed herein have been described in terms of the preferred embodiments above, numerous modifications and/or additions to the above-described preferred embodiments would be readily apparent to one skilled in the art. By way of example, but not limitation, the inventions include any combination of the elements from the various species and embodiments disclosed in the specification that are not already described. It is intended that the scope of the present inventions extend to all such modifications and/or additions and that the scope of the present inventions is limited solely by the claims set forth below.