U.S. patent application number 16/852457 was filed with the patent office on 2020-07-30 for cochlear implants and magnets for use with same.
The applicant listed for this patent is ADVANCED BIONICS AG. Invention is credited to Sung Jin Lee, James George Elcoate Smith.
Application Number | 20200238088 16/852457 |
Document ID | 20200238088 / US20200238088 |
Family ID | 1000004765891 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200238088 |
Kind Code |
A1 |
Smith; James George Elcoate ;
et al. |
July 30, 2020 |
COCHLEAR IMPLANTS AND MAGNETS FOR USE WITH SAME
Abstract
A cochlear implant including a cochlear lead, a housing, a
magnet apparatus located within the flexible housing and including
a first partial disk shaped magnet member and a second partial disk
shaped magnet member spaced apart from the first partial disk
shaped magnet member, an antenna within the housing, and a
stimulation processor.
Inventors: |
Smith; James George Elcoate;
(Santa Clarita, CA) ; Lee; Sung Jin; (Valencia,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ADVANCED BIONICS AG |
Staefa |
|
CH |
|
|
Family ID: |
1000004765891 |
Appl. No.: |
16/852457 |
Filed: |
April 18, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15805025 |
Nov 6, 2017 |
10646718 |
|
|
16852457 |
|
|
|
|
62422548 |
Nov 15, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36038 20170801;
A61N 1/3787 20130101; A61N 1/086 20170801; A61N 1/0541 20130101;
A61N 1/375 20130101; A61N 1/08 20130101; A61N 1/37217 20130101 |
International
Class: |
A61N 1/375 20060101
A61N001/375; A61N 1/05 20060101 A61N001/05; A61N 1/08 20060101
A61N001/08; A61N 1/372 20060101 A61N001/372; A61N 1/378 20060101
A61N001/378; A61N 1/36 20060101 A61N001/36 |
Claims
1-10. (canceled)
11. A cochlear implant, comprising: a cochlear lead including a
plurality of electrodes; a flexible housing including a magnet
pocket, a top wall above the magnet pocket that does not include an
opening into the magnet pocket, and a bottom wall below the magnet
pocket that does not include an opening into the magnet pocket; a
magnet apparatus, located within the magnet pocket, including a
magnetic element, which defines an outer surface, a diameter, a
thickness and the diameter to thickness ratio ("DtoT ratio") that
is 2.5 or less, and a hermetically sealed housing that covers the
outer surface of the magnetic element; an antenna within the
housing and adjacent to the magnet pocket; and a stimulation
processor operably connected to the antenna and to the cochlear
lead.
12. A cochlear implant as claimed in claim 11, wherein the magnet
apparatus defines a cylindrical shape.
13. A cochlear implant as claimed in claim 11, wherein the
hermetically sealed housing is 0.2 to 0.3 mm thick.
14. A cochlear implant as claimed in claim 11, wherein the diameter
of the magnetic element is 7.1 mm or less; and the thickness of the
magnetic element is 2.8 mm or more.
15. A cochlear implant as claimed in claim 11, wherein the antenna
and the magnet apparatus are embedded in the flexible housing.
16. A cochlear implant as claimed in claim 11, wherein the
respective configurations of the flexible housing and the magnet
apparatus are such that the magnet apparatus will rotate and
distort the flexible housing in response to the presence of a
magnetic field of at least 1.5 T.
17. A cochlear implant as claimed in claim 11, wherein the DtoT
ratio ranges from 2.5 to 1.9.
18. A system, comprising a cochlear implant as claimed in claim 11;
and a headpiece including an antenna, and a headpiece magnet
associated with the antenna that is attracted to the implant
magnet.
19. A system, comprising a cochlear implant as claimed in claim 11;
a sound processor; and a headpiece, operably connected to the sound
processor, including an antenna, and a headpiece magnet associated
with the antenna that is attracted to the implant magnet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Prov. App. Ser. No.
62/422,548, filed Nov. 15, 2016, which is incorporated herein by
reference.
BACKGROUND
1. Field
[0002] The present disclosure relates generally to the implantable
portion of implantable cochlear stimulation (or "ICS") systems.
2. Description of the Related Art
[0003] 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.TM. BTE sound
processor, the Naida.TM. CI Q Series sound processor and the
Neptune.TM. body worn sound processor, which are available from
Advanced Bionics.
[0004] 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.
[0005] 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. The magnet 24 is also relatively thin in conventional cochlear
implants in order to provide a relatively thin implant.
[0006] There are some instances where it is necessary to remove the
magnet from a conventional 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
positioning magnet 24 has a diameter of 10.5 mm and a thickness of
2.2 mm. 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. 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.
[0007] The present inventors have determined that conventional
cochlear implants are susceptible to improvement. For example,
removal and replacement of the implant magnet by way of the
aperture may be required because some conventional cochlear
implants are not 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'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, dislodge the implant magnet 24 from the pocket 26 and
reorient the magnet in the manner illustrated in FIG. 4. In some
instances, the implant magnet 24 may rotate 180 degrees, thereby
reversing the N-S orientation of the magnet. The present inventors
have determined that such reorientation (and reversal) may also
occur if there is no aperture in the flexible housing, and the
magnet is embedded within a closed pocket, due to the softness of
the material (e.g., silicone) used to form the housing.
[0008] Reorientation of the magnet 24 can place significant stress
on the dermis (or "skin"), which cause significant pain. Prior to
rotation (FIG. 3), the distance D1.sub.PA between the skull bone
below the cochlear implant and the skin above the implant is
relatively small, i.e., slightly greater than the thickness of the
implant magnet 24. The distance between the bone and skin greatly
increases to distance D2.sub.PA when the implant magnet 24 rotates
to the orientation illustrated in FIG. 4. In fact, because the
diameter of the magnet 24 is far greater than the thickness, the
difference .DELTA.D.sub.PA is significantly greater than the
original distance D1.sub.PA.
[0009] As alluded to above, magnet rotation may be avoided by
surgically removing the magnet prior to the MRI procedure. However,
in addition to the issues associated with the removal/replacement
surgery, the presence of the magnet aperture 28 can lead to the
formation of biofilm and can allow ingress of bacteria and
microbes. Accordingly, the present inventors have determined that a
solution which allows an MRI procedure to be performed without
magnet removal/replacement surgery, thereby eliminating the need
for the magnet aperture, would be desirable.
SUMMARY
[0010] A cochlear implant in accordance with one of the present
inventions includes a cochlear lead, a housing, a magnet apparatus,
located within the flexible housing, including a first partial disk
shaped magnet member and a second partial disk shaped magnet member
spaced apart from the first partial disk shaped magnet member, an
antenna within the housing, and a stimulation processor. The
present inventions also include systems with such a cochlear
implant in combination with a headpiece, as well as systems with
such a cochlear implant in combination with both a headpiece and a
sound processor.
[0011] A cochlear implant in accordance with one of the present
inventions includes a cochlear lead including a plurality of
electrodes, a flexible housing including a magnet pocket, a top
wall above the magnet pocket that does not include an opening into
the magnet pocket, and a bottom wall below the magnet pocket that
does not include an opening into the magnet pocket, a magnetic
element, located within the magnet pocket, that defines a diameter,
a thickness and the diameter to thickness ratio ("DtoT ratio") that
is 2.5 or less, an antenna within the housing, and a stimulation
processor. The present inventions also include systems with such a
cochlear implant in combination with a headpiece, as well as
systems with such a cochlear implant in combination with both a
headpiece and a sound processor.
[0012] There are a number of advantages associated with such
apparatus and systems. For example, when torque applied to the
magnet apparatus by a strong magnetic field rotates the magnet
apparatus, the increase in distance between the bone and skin (as
well as the associated stress on the dermis and pain) will be far
less than that associated with a conventional cochlear implant. As
a result, surgical removal of the cochlear implant magnet prior to
an MRI procedure, and then surgical replacement thereafter, is not
required and the magnet aperture may be omitted.
[0013] 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
[0014] Detailed descriptions of the exemplary embodiments will be
made with reference to the accompanying drawings.
[0015] FIG. 1 is a plan view of a conventional cochlear
implant.
[0016] FIG. 2 is a section view taken along line 2-2 in FIG. 1.
[0017] FIG. 3 is a section view showing the conventional cochlear
implant as an MRI magnetic field is being applied.
[0018] FIG. 4 is a section view showing the result of the
application of the MRI magnetic field to the conventional cochlear
implant.
[0019] FIG. 5 is a plan view of a cochlear implant in accordance
with one embodiment of a present invention.
[0020] FIG. 6 is a section view taken along line 6-6 in FIG. 5.
[0021] FIG. 7 is a portion of FIG. 6 with the magnet apparatus
removed.
[0022] FIG. 8 is a perspective view of a portion of the cochlear
implant illustrated in FIG. 5.
[0023] FIG. 9 is a section view taken along line 9-9 in FIG. 8.
[0024] FIG. 10 is a section view of the cochlear implant
illustrated in FIG. 5 prior to the application of a MRI magnetic
field.
[0025] FIG. 11 is a section view showing the result of the
application of the MRI magnetic field to the cochlear implant
illustrated in FIG. 10.
[0026] FIG. 12 is a section view of a cochlear implant in
accordance with one embodiment of a present invention.
[0027] FIG. 13 is a perspective view of a portion of the cochlear
implant illustrated in FIG. 12.
[0028] FIG. 14 is a section view taken along line 14-14 in FIG.
13.
[0029] FIG. 15 is a partial section view of a cochlear implant in
accordance with one embodiment of a present invention.
[0030] FIG. 16 is a side view of a portion of the cochlear implant
illustrated in FIG. 15.
[0031] FIG. 17 is a perspective view of a portion of the cochlear
implant illustrated in FIG. 15.
[0032] FIG. 18 is a side view of a portion of the cochlear implant
illustrated in FIG. 15 in a partially rotated state.
[0033] FIG. 19 is a side view of a portion of the cochlear implant
illustrated in FIG. 15 in a partially rotated state.
[0034] FIG. 20 is a section view of a cochlear implant in
accordance with one embodiment of a present invention.
[0035] FIG. 21 is a side view of a portion of the cochlear implant
illustrated in FIG. 20.
[0036] FIG. 22 is a plan view of a portion of the cochlear implant
illustrated in
[0037] FIG. 20.
[0038] FIG. 23 is a section view showing the result of an
application of a MRI magnetic field to the cochlear implant
illustrated in FIG. 20.
[0039] FIG. 24 is a block diagram of a cochlear implant system in
accordance with one embodiment of a present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0040] 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.
[0041] One example of a cochlear implant (or "implantable cochlear
stimulator") in accordance with the present inventions is the
cochlear implant 100 illustrated in FIGS. 5-9. Referring first to
FIG. 5, the exemplary cochlear implant 100 includes a resilient
flexible housing 102 formed from a silicone elastomer or other
suitable material (e.g., with a hardness from 50 to 70 Shore A), 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 apparatus 124 is located within
an antenna portion 125 of the housing 102. The magnet apparatus
124, which is used to maintain the position of a headpiece
transmitter over the antenna 108, is centered relative to the
antenna 108.
[0042] Turning to FIGS. 6-9, the exemplary magnet apparatus 124
includes first and second magnet portions 126a and 126b which have
complementary shapes that together define the overall shape of the
magnet apparatus. In the illustrated implementation, the magnet
apparatus 124 has an overall frustoconical shape with a circular
(or substantially circular) bottom and a circular (or substantially
circular) top. The first and second magnet portions 126a and 126b
each have a partial disk shape and, to that end, have respective
partial disk shaped top surfaces 128a and 128b, partial disk shaped
bottom surfaces 130a and 130b, outer side surfaces 132a and 132b,
and inner side surfaces 134a and 134b that face one another. As
used herein, a "partial disk shaped" includes an arcuate edge of
about 180 degrees (i.e., 180 degree.+-.5%) and a non-arcuate edge
that extends from one end of the arcuate edge to the other. In a
cross-section extending through the inner side surface 134a and
134b, the first magnet portion 126a has parallelogram shape (with
rounded corners) and the second magnet portion 126b has a trapezoid
shape (with rounded corners). The first and second magnet portions
126a and 126b also have the same N-S orientation.
[0043] The exemplary first and second magnet portions 126a and 126b
are respectively located within magnet pockets 136a and 136b in the
housing antenna portion 125 which, in their unstressed states, have
sizes and shapes corresponding to those of the first and second
magnet portions. In the illustrated implementation, the magnet
portions 126a and 126b are embedded within the housing 102 such
that, when the cochlear implant 100 is in its flat state (FIG. 6)
without any rotation of the magnet portions 126a and 126b, the
magnet portions are in contact with the resilient material that
forms the housing and there are no gaps between the magnet portions
and the inner surfaces of the magnet pockets. In particular, the
magnet pockets 136a and 136b are surrounded by, and defined by, a
bottom wall 138 that is located under the magnet pockets (in the
illustrated orientation), a top wall 140 that is located above the
magnet pockets (in the illustrated orientation), a side wall 142
that is lateral of, and extends around, the magnet pockets and a
divider wall 144 that is located between the magnet pockets as well
as between the magnet portions 126a and 126b. There are no openings
in the bottom wall 138 or the top wall 140 for removal of the
magnet apparatus 124. It should also be noted that the silicone
elastomer (or other suitable resilient material) is stiff enough to
maintain the magnet portions 126a and 126b in the illustrated
orientation, in the absence of a strong external magnet filed,
despite the N-N and S-S polar alignment of the magnet portions. The
resilient material will, however, allow the magnet portions 126a
and 126b to rotate in the manner described below with reference to
FIGS. 10 and 11 when exposed to a MRI magnetic field. In some
instances, a lubricious coating may be applied to the exterior of
the magnet portions 126a and 126b to reduce the friction between
magnet portions and the housing 102, thereby reducing torque.
Suitable lubricious coatings include hydrophilic hydrogel and
diamond-like carbon, both of which would significantly reduce
friction and are biocompatible.
[0044] Although the present inventions are not so limited, the
magnet portions 126a and 126b of the exemplary magnet apparatus 124
include respective magnetic elements 146a and 146b (FIG. 6) formed
from a ferromagnetic material (e.g., N35 grade neodymium) and thin
hermetically sealed housings 148a and 148b formed from, for
example, biocompatible metals and/or plastics.
[0045] 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 the overall size of the magnet
apparatus 124, the top diameter may be about 10.6 to 12.6 mm, the
bottom diameter may be about 12.3 to 14.3 mm, and the thickness T
(FIG. 9) may be about 2.2 to 3.0 mm. So configured, the width of
the magnet portions 126a and 126b, i.e. the dimension perpendicular
to the thickness T and to the axis of rotation AR, may be about 5.9
to 6.2 mm. The divider wall 144 adds about 1.0 mm to the diameters
in the direction perpendicular to the wall.
[0046] Reorientation of the magnet portions 126a and 126b of the
exemplary magnet apparatus 124 causes significantly less stress on
the dermis and, accordingly, less pain than conventional implant
magnets. Such rotation may be imparted by an MRI magnetic field.
Prior to rotation when the cochlear implant is in the flat state
(FIG. 10), the distance D1 between the skull bone below the
cochlear implant and the skin above the implant is relatively
small. This distance is approximately the same as distance
D1.sub.PA (FIG. 3) of the conventional cochlear implant. The
distance between the bone and skin increases only slightly by
difference .DELTA.D to distance D2 when the implant magnet portions
126a and 126b rotate separately about their own axis of rotation AR
(FIG. 9) to the orientation illustrated in FIG. 11, which shows the
exemplary cochlear implant in a distended state. Such rotation also
causes the portions of the housing 102 that define the magnet
pockets 136a and 136b (as well as the pockets themselves) to
stretch and distort. The resilience of the housing material will
typically drive the implant magnet portions 126a and 126b to their
flat-state orientations when the MRI magnetic field is removed. In
some instances, however, the clinician may need to press on the
skin over the magnet apparatus to drive the magnet portions back to
their flat-state orientations.
[0047] It should be noted here that for a given rotational
magnitude (e.g., about 75 degrees in FIGS. 4 and 11), the distances
.DELTA.D and D2 (FIG. 11) associated with the implant magnet
portions 126a and 126b are considerably less than the distances
.DELTA.D.sub.PA and D2.sub.PA (FIG. 4) of the conventional cochlear
implant magnet 24. This difference stems from the fact that the
width W of the magnet portions 126a and 126b is far smaller than
the diameter of the convention disk-shaped magnet 24.
[0048] The present magnet assembles (and associated magnet
portions) are not limited to the configuration illustrated in FIGS.
5-11. To that end, the exemplary cochlear implant 200 illustrated
in FIGS. 12-14 is identical to the implant 100 but for the magnet
apparatus 224 and slightly differently shaped pockets 236a and 236b
in housing 202. The magnet apparatus 224 has an overall cylindrical
disk shape (as opposed to a frustoconical disk shape) defined by
partial disk shaped magnet portions 226a and 226b. The magnet
portions 226a and 226b are identical to one another and each
include a partial disk shaped top surface 228, a partial disk
shaped bottom surface 230, an outer side surface 232, and an inner
side surface 234. In a cross-section perpendicular to the inner
side surfaces 234, the magnet portions have a rectangular shape
(with rounded corners). The magnet portions 226a and 226b also each
include a magnetic element 246 and a thin hermetically sealed
housing 248 formed from the materials described above. When exposed
to an MRI magnetic field, the magnet apparatus 224 will behave in
the manner described above with reference to FIGS. 10 and 11.
[0049] Turning to FIGS. 15-17, the exemplary cochlear implant 300
is similar to cochlear implant 200 and similar elements are
represented by similar reference numerals. Here, however, the
magnet apparatus 324 includes two partial disk shaped magnet
portions 226a and 226b that are tethered to one another in a manner
that allows magnet portions 226a and 226b to rotate, but limits the
rotation to a predetermined amount. The housing 302 includes a
single magnet pocket 336 to accommodate tethered arrangement. In
the illustrated implementation, the magnet portions 226a and 226b
are tethered to one another with a flexible strap 350. The flexible
strap 350 includes end portions 352a and 352b, which are
respectively secured to the magnet portions 226a and 226b, and an
intermediate portion 354 that is not secured to either magnet
portion. For example, the end portions 352a and 352b may be secured
to the bottom surfaces 230 of the magnet portions 226a and 226b
with an adhesive or other suitable instrumentality. The end
portions 352a and 352b are not secured to any other surfaces. In
other implementations, the end portions 352a and 352b may be
secured to more than one surface of one or both of the magnet
portions 226a and 226b and/or may be secured to different surfaces
(or sets of surfaces) on the magnet portions 226a and 226b.
Suitable materials for the flexible strap 250 include, but are not
limited to, a nylon cloth strap or Kapton.RTM. (polyimide film)
tape, including those with reinforcing fibers (e.g., Kevlar.RTM. or
polyethylene fibers). It should also be noted here that the housing
302 may be formed in two steps, with a bottom cap overmolded onto
the remainder of the housing (and formed from the same material as
the remainder of the housing) after the tethered magnet portions
226a and 226b have been inserted into the pocket 336.
[0050] Although the amount of allowed rotation may vary from one
implementation to another, the flexible strap 350 in the
illustrated implementation allows the magnet portions 226a and 226b
to rotate up to approximately 135 degrees form the flat-state
orientation illustrated in FIGS. 15-17 in response to the presence
of an MRI magnetic field. The magnet portions 226a and 226b may,
for example, rotate to the orientation illustrated in FIG. 18 in
some instances. Rotation beyond the orientation illustrated in FIG.
19 is, however, prevented by the strap 250. As a result, an MRI
magnetic field will not cause the N-S orientations of the magnet
portions 226a and 226b to be completely reversed.
[0051] Referring to FIGS. 20-23, the stress on the skin (and
associated pain) may also be reduced by employing particular magnet
diameter to thickness ratios ("D/T ratios"). To that end, the
exemplary cochlear implant 400 illustrated in FIG. 20 is similar to
cochlear implant 300 and similar elements are represented by
similar reference numerals. Here, however, the magnet apparatus 424
is a unitary structure which does not include a pair of magnet
portions. The magnet apparatus 424 has a cylindrical disk shape and
includes a circular top surface 428, a circular bottom surface 430,
and an outer side surface 432, and is formed from a magnetic
element 446 and a thin hermetically sealed housing 448 that covers
the outer surface of, and has the same overall shape as, the
magnetic element. In a cross-section through the diameter, the
magnet apparatus 424 has a rectangular shape (with rounded
corners).
[0052] The exemplary magnetic element 446 may have a DtoT ratio of
2.5 or less. To that end, the exemplary magnetic element 446 has a
diameter DIA of 7.1 mm, a thickness T of 2.8 mm, and a DtoT ratio
of 2.5. In another exemplary embodiment, the magnetic element may
have a diameter DIA of 6.5 mm, a thickness T of 3.5 mm, and a DtoT
ratio of 1.9. In other embodiments, the DtoT ratio may range from
2.5 to 1.9, with magnetic element diameters of 7.1 or less, and
magnet thicknesses of 2.8 or more. The dimensions magnet apparatus
also include the thin housing 448, which adds about 0.2 to 0.3 mm
to the diameters and thicknesses discussed above. For purposes of
comparison, the conventional magnet 24 illustrated in FIGS. 1-4,
which has a diameter of 10.5 mm and a thickness of 2.2 mm, has a
DtoT ratio of 4.8. Suitable material for the magnetic element 446
includes N52 grade neodymium, and suitable materials for the
housing 448 include the housing materials described above.
[0053] Referring to FIG. 23, the magnet apparatus 424 will rotate
in a manner similar to the conventional magnet 24 when exposed to
an MRI magnetic field. However, the distances .DELTA.D and D3
associated with the magnet apparatus 424 are considerably less than
the distances .DELTA.D.sub.PA and D2.sub.PA of the conventional
cochlear implant. This difference stems from the fact that the
diameter of the magnet apparatus 424 is smaller than the diameter
of the convention disk-shaped magnet 24. As a result, reorientation
of the magnet apparatus 424 causes significantly less stress on the
dermis and, accordingly, less pain than the conventional implant
magnet 24.
[0054] As illustrated in FIG. 24, the exemplary cochlear implant
system 50 includes the cochlear implant 100 (or 200 or 300 or 400),
a sound processor, such as the illustrated body worn sound
processor 200 or a behind-the-ear sound processor, and a headpiece
300.
[0055] The exemplary body worn sound processor 500 in the exemplary
ICS system 50 includes a housing 502 in which and/or on which
various components are supported. Such components may include, but
are not limited to, sound processor circuitry 504, a headpiece port
506, an auxiliary device port 508 for an auxiliary device such as a
mobile phone or a music player, a control panel 510, one or
microphones 512, and a power supply receptacle 514 for a removable
battery or other removable power supply 516 (e.g., rechargeable and
disposable batteries or other electrochemical cells). The sound
processor circuitry 504 converts electrical signals from the
microphone 512 into stimulation data. The exemplary headpiece 600
includes a housing 602 and various components, e.g., a RF connector
604, a microphone 606, an antenna (or other transmitter) 608 and a
positioning magnet apparatus 610, that are carried by the housing.
The magnet apparatus 610 may consist of a single magnet or may
consist of one or more magnets and a shim. The headpiece 600 may be
connected to the sound processor headpiece port 506 by a cable 612.
The positioning magnet apparatus 610 is attracted to the magnet
apparatus 124 of the cochlear stimulator 100, thereby aligning the
antenna 608 with the antenna 108. The stimulation data and, in many
instances power, is supplied to the headpiece 600. The headpiece
600 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.
[0056] In at least some implementations, the cable 612 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) 512 on the sound processor 500, the microphone
606 may be also be omitted in some instances. The functionality of
the sound processor 500 and headpiece 600 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.
[0057] 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.
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