U.S. patent application number 15/568469 was filed with the patent office on 2018-04-26 for cochlear implants having mri-compatible magnet apparatus and associated methods.
The applicant listed for this patent is ADVANCED BIONICS AG, Sung Jin LEE, Jeryle L. WALTER. Invention is credited to Sung Jin Lee, Jeryle L. Walter.
Application Number | 20180110985 15/568469 |
Document ID | / |
Family ID | 53396586 |
Filed Date | 2018-04-26 |
United States Patent
Application |
20180110985 |
Kind Code |
A1 |
Walter; Jeryle L. ; et
al. |
April 26, 2018 |
COCHLEAR IMPLANTS HAVING MRI-COMPATIBLE MAGNET APPARATUS AND
ASSOCIATED METHODS
Abstract
A cochlear implant is disclosed, including a cochlear lead, an
antenna, a stimulation processor, a magnet apparatus, associated
with the antenna, including a case and a plurality of magnetic
material particles within the case that are movable relative to one
another.
Inventors: |
Walter; Jeryle L.;
(Valencia, CA) ; Lee; Sung Jin; (Valencia,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WALTER; Jeryle L.
LEE; Sung Jin
ADVANCED BIONICS AG |
Valencia
Valencia
Staefa |
CA
CA |
US
US
CH |
|
|
Family ID: |
53396586 |
Appl. No.: |
15/568469 |
Filed: |
May 28, 2015 |
PCT Filed: |
May 28, 2015 |
PCT NO: |
PCT/US2015/033040 |
371 Date: |
October 21, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/37229 20130101;
A61N 1/0541 20130101; A61N 1/375 20130101; H04R 2225/67 20130101;
A61N 1/36038 20170801; A61N 1/086 20170801 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/372 20060101 A61N001/372; A61N 1/375 20060101
A61N001/375 |
Claims
1. A cochlear implant, comprising: a cochlear lead including a
plurality of electrodes; an antenna; a stimulation processor
operably connected to the antenna and to the cochlear lead; and a
magnet apparatus, associated with the antenna, including a case and
a plurality of magnetic material particles packed within the case
in such a manner that adjacent magnetic material particles are in
contact with one another and are also movable relative to one
another.
2. A cochlear implant as claimed in claim 1, wherein the magnetic
material particles are rotatable relative to one another.
3. A cochlear implant as claimed in claim 1, wherein the magnetic
material particles are each are free to move from one X-Y-Z
coordinate to another and to rotate in any direction.
4. A cochlear implant as claimed in claim 1, wherein the magnetic
material particles are at least substantially polyhedral in
shape.
5. A cochlear implant as claimed in claim 1, wherein the magnetic
material particles define mesh sizes that range from 50 .mu.m to
500 .mu.m, or from 100 .mu.m to 300 .mu.m, or from 300 .mu.m to 500
.mu.m.
6. A cochlear implant as claimed in claim 1, wherein the magnetic
material particles are formed from a material selected from the
group consisting of neodymium-iron-boron, magnetic material,
isotropic neodymium, anisotropic neodymium, samarium-cobalt.
7. A cochlear implant as claimed in claim 1, wherein the case
comprises a disk-shaped case.
8. A cochlear implant as claimed in claim 1, wherein the case is
formed from a material selected from the group consisting of
paramagnetic metal and plastic.
9. A cochlear implant as claimed in claim 1, further comprising: a
magnetic field focusing shim located within the case.
10. A cochlear implant as claimed in claim 1, wherein the antenna,
the stimulation processor and the magnet apparatus are located
within a flexible housing.
11. A cochlear implant as claimed in claim 1, wherein the magnet
apparatus defines a strength of at least 60-70 gauss measured at a
distance of 1 mm from the case.
12. A cochlear implant as claimed in claim 1, wherein the case has
an internal volume and includes a divider that separates the
internal volume into a plurality of sub-volumes.
13. A method, comprising the step of: in response to the
application of a magnetic field defining a magnetic field direction
to an implantable cochlear stimulator including an antenna and a
magnet apparatus, associated with the antenna, having a case and a
plurality of magnetic material particles packed within the case in
the absence of a carrier and with adjacent magnetic material
particles in contact with one another, allowing the magnetic field
to rotate the magnetic material particles in any direction,
relative to the case, into magnetic alignment with the magnetic
field.
14. A method as claimed in claim 13, wherein the magnetic field has
a magnetic flux density of at least 1.5 Tesla.
15. A method as claimed in claim 13, wherein the magnetic field
comprises a MRI magnetic field.
16. A method as claimed in claim 13, wherein the step of allowing
the magnetic field to rotate the magnetic material particles
comprises allowing the magnetic field to rotate the magnetic
material particles in any direction, relative to the case and
relative to one another, into magnetic alignment with the magnetic
field.
17. A method as claimed in claim 13, wherein the step of allowing
the magnetic field to rotate the magnetic material particles
comprises allowing the magnetic field to move from one X-Y-Z
coordinate to another and to rotate in any direction relative to
the case and relative to one another into magnetic alignment with
the magnetic field.
18. A method as claimed in claim 13, wherein the magnetic material
particles are at least substantially polyhedral in shape.
19. A method as claimed in claim 13, wherein the magnetic material
particles define mesh sizes that range from 50 .mu.m to 500 .mu.m,
or from 100 .mu.m to 300 .mu.m, or from 300 .mu.m to 500 .mu.m.
20. A method as claimed in claim 13, further comprising the step
of: in response to movement of the implantable cochlear stimulator
within the magnetic field subsequent to the magnetic material
particles having been rotated into alignment with the magnetic
field, allowing the magnetic field to further rotate the magnetic
material particles in any direction, relative to the case, back
into magnetic alignment with the magnetic field.
21. A method as claimed in claim 13, wherein the magnet apparatus
defines a strength of at least 60-70 gauss measured at a distance
of 1 mm from the case.
22. A system, comprising a cochlear implant as claimed in claim 1;
and a headpiece including an antenna, and a headpiece magnet
apparatus associated with the antenna; wherein the cochlear implant
magnet apparatus and the headpiece magnet apparatus are
respectively configured such that a pull force is defined there
between that is equal to about 2.2.+-.0.1 N when the cochlear
implant magnet apparatus and the headpiece magnet apparatus are
separated by a distance of 3 mm.
23. A system as claimed in claim 22, wherein the headpiece magnet
apparatus includes a magnetic field focusing shim.
24. A system as claimed in claim 22, wherein the headpiece magnet
apparatus includes a plurality of magnets.
Description
BACKGROUND
1. Field
[0001] The present disclosure relates generally to the implantable
portion of implantable cochlear stimulation (or "ICS") systems.
2. Description of the Related Art
[0002] 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.TM.
Harmony.TM. BTE sound processor, the Advanced Bionics.TM. Naida.TM.
BTE sound processor and the Advanced Bionics.TM. Neptune.TM. body
worn sound processor.
[0003] 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.
[0004] The present inventors have determined that conventional
cochlear implants are susceptible to improvement. For example, the
magnets in many conventional cochlear implants are disk-shaped and
have north and south magnetic dipoles that are aligned in the axial
direction of the disk. Such magnets are not compatible with
magnetic resonance imaging ("MRI") systems. In particular, the
cochlear implant 10 illustrated in FIG. 1 includes, among other
things, a housing 12 and a disk-shaped solid block magnet 14.
[0005] The implant magnet produces a magnetic field M in a
direction that is perpendicular to the patient's skin and parallel
to the axis A, and 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 demagnetize
the implant magnet 14 or generate a significant amount of torque T
on the implant magnet 14. The torque T may dislodge the implant
magnet 14 from the pocket within the housing 12, reverse the magnet
14 and/or dislocate the cochlear implant 10, all of which may also
induce tissue damage. One proposed solution involves surgically
removing the implant magnet 14 prior to the MRI procedure and then
surgically replacing the implant magnet thereafter. The present
inventors have determined that a solution which does not involve
surgery would be desirable.
SUMMARY
[0006] A cochlear implant in accordance with one of the present
inventions includes a cochlear lead, an antenna, a stimulation
processor, a magnet apparatus, associated with the antenna,
including a case and a plurality of magnetic material particles
within the case that in contact with one another and are movable
relative to one another.
[0007] A method in accordance with one of the present inventions
may be practice in conjunction with an implantable cochlear
stimulator including an antenna and a magnet apparatus, associated
with the antenna, having a case and a plurality of magnetic
material particles within the case that are in contact with one
another. In response to the application of a magnetic field
defining a magnetic field direction to the implantable cochlear
stimulator, the magnetic field is allowed to rotate the magnetic
material particles in any direction, relative to the case, into
magnetic alignment with the magnetic field.
[0008] A system in accordance with one of the present inventions
includes cochlear implant, with a cochlear lead, an antenna, a
stimulation processor, a magnet apparatus, associated with the
antenna, including a case and a plurality of magnetic material
particles within the case that are in contact with one another and
movable relative to one another, and headpiece.
[0009] There are a number of advantages associated with such
apparatus and methods. For example, a strong magnetic field, such
as an MRI magnetic field, will not demagnetize the magnet
apparatus. Nor will it generate a significant amount of torque on
the magnet apparatus and associated cochlear implant. As a result,
surgical removal of the cochlear implant magnet prior to an MRI
procedure, and then surgically replacement thereafter, is not
required.
[0010] 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
[0011] Detailed descriptions of the exemplary embodiments will be
made with reference to the accompanying drawings.
[0012] FIG. 1 is a plan view showing a conventional cochlear
implant in an MRI magnetic field.
[0013] FIG. 2A is a perspective view of an implant magnet apparatus
in accordance with one embodiment of a present invention.
[0014] FIG. 2B is a section view taken along line 2B-2B in FIG.
2A.
[0015] FIG. 2C is a section view of an implant magnet apparatus in
accordance with one embodiment of a present invention.
[0016] FIG. 3A is a section view of an implant magnet apparatus in
accordance with one embodiment of a present invention.
[0017] FIG. 3B is a section view of an implant magnet apparatus in
accordance with one embodiment of a present invention.
[0018] FIG. 3C is a perspective view showing the interior of a
portion of an implant magnet apparatus in accordance with one
embodiment of a present invention.
[0019] FIG. 4A is a magnified view of exemplary magnetic
particles.
[0020] FIG. 4B is a magnified view of exemplary magnetic particles
in a loosely packed state
[0021] FIG. 5A is a perspective view of a plurality of magnetic
particles a loosely packed state prior to being exposed to a
magnetic field.
[0022] FIG. 5B is a perspective view of a plurality of magnetic
particles a loosely packed state after being exposed to a magnetic
field.
[0023] FIG. 6A is a section view of the implant magnet apparatus
illustrated in FIG. 2 prior to being exposed to a magnetic
field.
[0024] FIG. 6B is a section view of the implant magnet apparatus
illustrated in FIG. 2 being exposed to a magnetic field.
[0025] FIG. 7 is a plan, cutaway view showing a cochlear implant in
accordance with one embodiment of a present invention being used in
conjunction with a cochlear implant headpiece.
[0026] FIG. 8 is a plan, cutaway view showing a cochlear implant in
accordance with one embodiment of a present invention being exposed
to an MRI magnetic field.
[0027] FIG. 9 is a plan, cutaway view showing a cochlear implant in
accordance with one embodiment of a present invention being exposed
to an MRI magnetic field.
[0028] FIG. 10 is a plan view of a cochlear implant in accordance
with one embodiment of a present invention.
[0029] FIG. 11 is a block diagram of a cochlear implant system in
accordance with one embodiment of a present invention.
[0030] FIG. 12 is a section view showing portions of a system in
accordance with one embodiment of a present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0031] 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.
[0032] As illustrated for example in FIGS. 2A and 2B, an exemplary
magnet apparatus 20 includes magnetic material particles (or
"particles") 22 within the internal volume of a case 24. The
particles 22, which are discussed in greater detail below with
reference to FIGS. 4A-6B, are in contact with one another and are
independently and freely rotatable and otherwise movable relative
to one another and to the case. The particles 22 are free to move
from one X-Y-Z coordinate to another and/or rotate in any
direction. For example, some particles 22 may move linearly and/or
rotate relative to other particles and relative to the case 24,
while the orientation of the case remains the same, when the magnet
apparatus 20 is exposed to an external magnetic field. The magnet
apparatus 20 may be incorporated into a cochlear implant in the
manner described in greater detail below with reference to FIGS.
7-11.
[0033] The case 24 is not limited to any particular configuration,
size or shape. In the illustrated implementation, the case 24
includes a base 26 and a cover 28 that may be secured to base after
the magnetic material particles 22 have been dispensed into the
base. The cover 28 may be secured to the base 26 in such a manner
that a hermetic seal is formed between the cover and the base.
Suitable techniques for securing the cover 28 to the base 26
include, for example, seam welding with a laser welder. With
respect to materials, the case 24 may be formed from biocompatible
paramagnetic metals, such as titanium or titanium alloys, and/or
biocompatible non-magnetic plastics such as 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), while exemplary metal thicknesses may range
from 0.20 mm to 0.25 mm. With respect to size and shape, the case
24 may have an overall size and shape similar to that of
conventional cochlear implant magnets so that the magnet apparatus
20 can be substituted for a conventional magnet in an otherwise
conventional cochlear implant. The exemplary case 24 is disk-shaped
and defines a central axis A. In some implementations, the diameter
that may range from 9 mm to 16 mm and the thickness may range from
1.5 mm to 3.0 mm. The diameter of the case 24 is 12.9 mm, and the
thickness is 2.4 mm, in the illustrated embodiment.
[0034] The magnet apparatus 20 includes an inner surface 30 which,
in this embodiment, is formed by the inner surface of the case 24,
i.e., the inner surfaces of the base 26 and cover 28. A lubricious
layer may be added to the inner surface to improve the movement of
the particles 22 that are adjacent to the inner surface 30. To that
end, and referring to the magnet apparatus 20a illustrated in FIG.
2C, which is otherwise identical to the magnet apparatus 20, a
lubricious layer 32 covers the inner surface 30 of the case 24. The
lubricious layer 32 may be in the form of a specific finish of the
inner surface that reduces friction, as compared to an unfinished
surface, or may be a coating of a lubricious material such as
polytetrafluoroethylene (PTFE), Parylene, or fluorinated ethylene
propylene (FEP). In those instances where the base 26 is formed by
stamping, the finishing process may occur prior to stamping.
[0035] The exemplary magnet apparatus 20b illustrated in FIG. 3A is
substantially similar to magnet apparatus 20 and similar elements
are represented by similar reference numerals. Here, however, a
shim 34 may be inserted into the case 24 to focus the magnetic
field created by the magnetic material particles 22. More
specifically, when the associated cochlear implant is implanted,
the shim 34 (sometimes referred to as a "flux guide") will increase
the flux density and focus the magnetic field toward the patient's
skin and an externally worn headpiece. Although the present shims
are not so limited, the exemplary shim 34 is cup-shaped and may be
about 0.25 mm thick and formed from iron or from a nickel-iron
alloy, referred to as mu-metal, that is composed of approximately
77% nickel, 16% iron, 5% copper and 2% chromium or molybdenum. In
other implementations, a flat disk positioned at the bottom of the
base 26 may be employed.
[0036] Referring to FIG. 3B, the exemplary magnet apparatus 20c is
substantially similar to magnet apparatus 20b in FIG. 3A and
similar elements are represented by similar reference numerals.
Here, however, a lubricious layer 32 covers the inner surface 30b
of the magnet apparatus 20c. The inner surface 30b is formed by the
inner surfaces of the cover 28 and the shim 34. The lubricious
layer 32 may be formed in the manner discussed above with reference
to FIG. 2C. In those instances where the shim 34 is formed by
stamping, the finishing process may occur prior to stamping.
[0037] The exemplary magnet apparatus 20d illustrated in FIG. 3C is
substantially similar to magnet apparatus 20 in FIG. 2A and similar
elements are represented by similar reference numerals. Here,
however, a divider 36 is located within the internal volume of case
24 (shown with the cover 28 removed). The divider 36, which may
include one or more walls 38 that extend from the bottom of the
case 24 to the top, separates the internal volume into a plurality
of sub-volumes 40 and facilitates an even distribution of the
magnetic material particles 22 within case 24 by limiting particle
migration. The even distribution of the magnetic material particles
22 provided by the divider 36 results in proper alignment of the
magnet apparatus 20 with the associated headpiece magnet or magnet
apparatus, which in turn results in proper alignment of the implant
antenna with the headpiece antenna. Although the exemplary divider
36 is X-shaped and divides the volume into four sub-volumes 40, any
suitable configuration and number of sub-volumes may be employed.
Other exemplary divider shapes include, but are not limited to, an
asterisk shape and a honey-comb shape. Suitable divider materials
include, but are not limited to, plastics such as PEEK and PTFE and
metals such as iron, titanium and mu-metal. A divider, such as
exemplary divider 36, may also be positioned within the other
magnet apparatus described herein, including magnet apparatus 20b
and magnet apparatus 20c.
[0038] Turning to FIGS. 4A and 4B, and although the present
magnetic material particles are not limited to any particular shape
unless so specified in a particular claim, the exemplary magnetic
material particles 22 are 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 herein may also be employed. The magnetic
material particles 22 may be formed from any suitable magnetic
material. Such materials include, but are not limited to,
neodymium-iron-boron ("Nd.sub.2Fe.sub.14B") magnetic material,
isotropic neodymium, anisotropic neodymium, samarium-cobalt
("Sm.sub.2Co.sub.17"). The at least substantially polyhedral shapes
illustrated in FIGS. 4A and 4B are the fractured pieces of a larger
magnet that are created by a magnet crushing process. The present
particles may have a mesh size that ranges from 50 .mu.m to 500
.mu.m, or from 100 .mu.m to 300 .mu.m, or from 300 .mu.m to 500
.mu.m, and the shape and size may vary from particle to particle.
The particles 22, which are not suspended in liquid or any other
carrier, may be packed loosely and pressed with a slight force of,
for example, 100 kPa (0.14 psi) in order to insure that adjacent
particles will be in contact with one another (FIG. 4B), yet will
also be independently movable and movable relative to one another.
To that end, and referring to FIGS. 5A and 5B, three exemplary
particles 22-1, 22-2 and 22-3 are shown in both arbitrary
orientations prior to being exposed to a magnetic field (FIG. 5A)
and after they have been aligned with a magnetic field (FIG. 5B).
The reorientation-related movement of the particles 22-1, 22-2 and
22-3, which varies from one particle to another, may entail
rotation about, and/or movement in the direction of, the X-axis,
the Y-axis, and/or the Z-axis, and any and all combinations
thereof.
[0039] The magnetic material density ratio within the case 24, i.e.
the ratio of the total volume of magnetic material particles to the
total volume within the case 24, may be at least 70%, i.e., there
is no more than 30% free space within the case. This ratio allows
the present magnet apparatuses 20-20d to be essentially the same
size and shape as a conventional disk-shaped permanent magnet in a
cochlear implant when combined with an appropriate headpiece. With
respect to the density of the magnetic material particles, the
density may range, in the exemplary context of
neodymium-iron-boron, from 2.75 g/cm.sup.3 (30% free space) to 3.94
g/cm.sup.3 (fully packed and pressed with a force of 100 kPa). Free
space percentages that are larger than 30% may be employed in those
instances where the magnet apparatus is larger. The magnetic
strength of the of the exemplary magnet apparatus 20b, which
includes the particles 22 within the case 24 and a shim 34, is
about 60-70 gauss measured at a distance of 1 mm from the case on
the axis A. The pull force between a cochlear implant including the
magnet apparatus 20 and a cochlear implant headpiece (e.g.,
headpiece 300 in FIG. 11), including headpieces that have one or
more magnets therein, at a distance of 3 mm may be about 2.2.+-.0.1
N. The 3 mm distance corresponds to the distance (or "air gap")
between the implant magnet apparatus and the headpiece magnet (or
magnet apparatus) during pull force testing, and the pull force
will be different at other testing distances. Various headpiece
magnet apparatus configurations which, when combined with an
implant magnet apparatus in a system that includes both a cochlear
implant and a cochlear implant headpiece, and where the pull force
between the headpiece magnet apparatus and the implant magnet
apparatus is about 2.2.+-.0.1 N, are discussed below with reference
to FIG. 12.
[0040] It should also be noted that the use of significantly larger
magnetic elements within the case in place of the magnetic material
particles will decrease the magnetic material density (due to air
gaps between the magnetic elements) and prevent magnet apparatus
which have cases of the sizes and shapes disclosed herein from
achieving the desired level of magnetic strength. Similarly, the
use of ferrofluids, which include nano-sized particles dispersed
and suspended within a fluid, in place of the magnetic material
particles would also necessitate the use of a case that is larger
than a conventional cochlear implant magnet to achieve the desired
level of magnetic strength.
[0041] For ease of illustration purposes on only, the non-spherical
particles may be represented in the manner shown in FIGS. 6A and
6B. The north pole N of each particle 22 is black (or grey) and the
south pole S is white. The respective N-S orientations of the
particles 22 will vary from one particle to the next, with the
particles being magnetically attracted to one other in arbitrary
directions, after the particles have been dispensed into the case
24. The particles 22 will remain in their random angular
orientations until they are reoriented by a magnetic field in the
manner described below. Such reorientation is possible because the
particles 22 are independently movable relative to one another in
any and all directions. Relative movement of the particles 22 may
entail rotation about the X-axis, or rotation about the Y-axis, or
rotation about the Z-axis, and/or any and all combinations thereof,
and/or non-rotational movement in the X-direction, or the
Y-direction, or the Z-direction, and/or any and all combinations
thereof.
[0042] An external magnetic field may be used to reorient the
magnetic material particles 22 within the case 24 to establish the
desired N-S orientation of magnet apparatuses 20-20d. Such
reorientation may be performed before or after the magnet
apparatuses 20-20d are incorporated into a cochlear implant. To
that end, and referring to FIG. 6B, the magnet apparatus may be
exposed to the magnetic field M of the magnet 32. With the
exception of those particles 22 that were by chance already aligned
with the magnetic field M, the particles 22 will rotate into
alignment with the magnetic field M (e.g., from the orientation
illustrated in FIG. 6A to the orientation illustrated in FIG. 6B),
thereby establishing the intended N-S orientation of the magnet
apparatus 20. Here, the intended N-S orientation is parallel to the
central axis A of the disk-shaped magnet apparatus 20.
[0043] The magnet apparatus 20 (or 20a-20d) may form part of a
cochlear implant in a cochlear implant system that also includes a
sound processor and a headpiece. One example of such a cochlear
implant system is the system 50, which is described in greater
detail below with reference to FIGS. 10 and 11, and which includes
a cochlear implant 100 and a headpiece 300. As illustrated for
example in FIG. 7, the implanted headpiece 100 includes the magnet
apparatus 20. The N-S orientation of the magnet apparatus 20 is the
same as the orientation illustrated in FIG. 6. The headpiece 300,
which includes a magnet apparatus 310 with the same N-S
orientation, may be held in place by virtue of the attraction
between the magnet apparatus 20 and the magnet apparatus 310. The
central axis A of the magnet apparatus 20 is perpendicular to the
patient's skin and parallel to the magnetic field M. Communication
between the headpiece 300 and cochlear implant 100 may then occur
in conventional fashion.
[0044] FIG. 8 shows the implanted cochlear implant 100 being
exposed to an MRI magnetic field B. The orientation of the cochlear
implant 100 is such that the central axis A of the magnet apparatus
20 is perpendicular to the MRI magnetic field B. In contrast to the
conventional magnet 14 illustrated in FIG. 1, however, the magnetic
field M of the magnet apparatus 20 is not perpendicular to the MRI
magnetic field B. Instead, the dominant MRI magnetic field B
reorients magnetic material particles 22 relative to the case 24
and to the associated cochlear implant, from the orientation
illustrated in FIG. 7 to the orientation illustrated in FIG. 8,
such that the N-S orientation of the magnet apparatus 20 is
perpendicular to the central axis A and the magnetic field M is
parallel to the MRI magnetic field B.
[0045] There are a variety of advantages associated with such
magnetic field reorientation. For example, the MRI magnetic field B
(typically 1.5 Tesla or more) will not demagnetize the magnet
apparatus 20 or generate a significant amount of torque T on the
magnet apparatus and associated cochlear implant. As a result,
surgical removal of the cochlear implant magnet prior to an MRI
procedure, and then surgically replacement thereafter, is not
required.
[0046] It should also be noted that movement of the patient
relative to the MRI magnetic field B while in the MRI magnetic
field B will also result in reorientation of the magnetic material
particles 22 within the case 24, as is illustrated in FIG. 9. Here,
the N-S orientation of the magnet apparatus 20 neither
perpendicular, nor parallel, to the central axis A and the magnetic
field M remains parallel to the MRI magnetic field B. The ability
of the particles 22 to rotate and move relative to the case 24
about and along the X, Y and Z-axes, as well as any and all
combinations of such rotation and movement (i.e., in any direction,
and any rotational direction, relative to the case and relative to
the remainder of the associated cochlear implant), allows the N-S
orientation of the each particle 22 (and the magnet apparatus 20)
to align itself with an MRI magnetic field B regardless of the
relative orientations of the MRI magnetic field and the magnet
apparatus. As the orientation of one or both of the MRI magnetic
field B and the magnet apparatus 20 changes, the N-S orientation of
the magnet apparatus 20 relative to the case 24 and central axis A
will change so as to maintain the alignment of the N-S orientation
of the magnetic material particles 22 (as well as the magnet
apparatus itself) with the MRI magnetic field.
[0047] After the MRI procedure has been completed, the implanted
magnet apparatus may be exposed to a magnetic field (e.g., with the
magnet 32) to return the particles 22 to their intended N-S
orientation.
[0048] One example of a cochlear implant (or "implantable cochlear
stimulator") including the present magnet apparatus 20 is the
cochlear implant 100 illustrated in FIG. 10. The cochlear implant
100 includes a 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, and a plurality of wires (not shown) that
extend through the flexible body from the electrodes 112a (e.g.,
platinum electrodes) in the array 112 to the other end of the
flexible body. The magnet apparatus 20 is located within a region
encircled by the antenna 108 (e.g., within an internal pocket 102a
defined by the housing 102) and insures that an external antenna
(discussed below) will be properly positioned relative to the
antenna 108. The exemplary processor assembly 104, which is
connected to the electrode array 112 and antenna 108, includes a
printed circuit board 114 with a stimulation processor 114a that is
located within a hermetically sealed case 116. The stimulation
processor 114a converts the stimulation data into stimulation
signals that stimulate the electrodes 112a of the electrode array
112.
[0049] Turning to FIG. 11, the exemplary cochlear implant system 50
includes the cochlear implant 100, a sound processor, such as the
illustrated body worn sound processor 200 or a behind-the-ear sound
processor, and a headpiece 300.
[0050] 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, as is
discussed below with reference to FIG. 12, 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 apparatus 20 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
antennae. The stimulation processor 114a converts the stimulation
data into stimulation signals that stimulate the electrodes 112a of
the electrode array 112.
[0051] 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.
[0052] Turning to FIG. 12, and as noted above, the respective
configurations of the magnet apparatus 20c (or 20-20b, 20d) in the
cochlear implant 100 and the magnet apparatus 308 in the headpiece
300 create a pull force there between that is about 2.2.+-.0.1 N
with a 3 mm air gap. The magnetic field generated by the magnet
apparatuses 20-20d is weaker than a similarly sized conventional
magnet apparatus that includes a solid block magnet in place of the
magnetic particles 22. The exemplary headpiece 300, on the other
hand, has a magnet apparatus 308 that is configured to generate a
stronger magnetic field than that associated with a conventional
headpiece having a similar configuration. As a result, the present
implant/headpiece system is able to provide the above-described
benefits associated with the movable magnetic particles without
increasing the thickness of the implant magnet and, accordingly,
the thickness of the implant itself, as compared of conventional
implants. The elements of the implant 100 and the headpiece 300
that are not discussed in the context of FIG. 12 have been omitted
from FIG. 12 for the sake of simplicity.
[0053] The exemplary magnet apparatus 308 illustrated in FIG. 12
includes a plurality of solid block magnets 309 and a shim 311. The
strength of the magnetic field associated with the headpiece may be
adjusted by replacing one or two of the magnets with a similarly
sized plastic spacer. In other implementations, a single, thick
magnet may be employed. The magnets 309 are disk-shaped in the
illustrated embodiment, but other shapes may be employed. The shim
311 increases the flux density and focus the magnetic field
associated with the magnets 309 toward the patient's skin and the
internal magnet apparatus 20c. Although the present shims are not
so limited, the exemplary shim 311 is cup-shaped and may be about
1.5 mm thick and formed from iron or mu-metal. In other
implementations, a flat disk positioned above the magnets 309 may
be employed.
[0054] By way of example, but not limitation, the following are
specific examples of the magnet apparatus 308 that will, in
combination with an implant 100 having the internal magnet
apparatus 20c and isotropic neodymium particles 22 with a mesh size
that ranges from 300 .mu.m to 500 .mu.m, provide a pull force of
about 2.2.+-.0.1 N when there is a spacing of about 3 mm between
the external magnet apparatus 308 and the internal magnet apparatus
20c. A magnet apparatus 308 with the shim 311 and three N52 magnets
that are 12.7 mm in diameter and 1.5 mm thick is one example.
Another example is a magnet apparatus 308 with the shim 311 and a
single N52 magnet that is 10.0 mm in diameter and 5.0 mm thick. In
those instances where even more pull force is required, e.g., where
a patient has a relatively thick skin flap, a magnet apparatus 308
with the shim 311 and a single N52 magnet that is 12.7 mm in
diameter and 5.0 mm thick may be employed. It should also be noted
that particles 22 having a mesh size that ranges from 100 .mu.m to
300 .mu.m may be used when the headpiece includes such a magnet
apparatus. In another otherwise identical example, which instead
employs anisotropic neodymium particles 22 with a mesh size that
ranges from 50 .mu.m to 200 .mu.m, the pull force is about
2.4.+-.0.1 N when there is a spacing of about 3 mm and the magnet
apparatus 308 includes two N52 magnets that are 12.7 mm in diameter
and 1.5 mm thick. The pull force at about 3 mm increases to about
3.0.+-.0.1 N when a third N52 magnet (12.7 mm in diameter and 1.5
mm thick) is added to the magnet apparatus 308.
[0055] 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. In some instances, a
lubricant such as vegetable oil may be applied to the particles 22
to reduce friction and improvement movement of the particles
relative to one another. 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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