Abstract:
An implantable medical device having a concave ceramic housing component; a concave metal housing component attached to the ceramic housing component to form a hermetically sealed enclosure; and an electronic trans-housing magnetic flux component disposed within the enclosure. Another aspect of the invention provides an implantable medical device having a ceramic housing component; a metal housing component; a circumferential sealing member attached to a periphery of the ceramic housing component and to a periphery of the metal housing component to form a hermetically sealed enclosure; and an electronic trans-housing magnetic flux component disposed within the enclosure. Still another aspect of the invention provides an implantable medical device with a first metal housing component; a second metal housing component, the second metal housing component forming an opening; a ceramic housing component disposed in the opening, the first metal housing component, the second metal housing component and the ceramic housing component cooperating to form a hermetically sealed enclosure; and an electronic trans-housing magnetic flux component disposed within the enclosure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/017,504, filed Dec. 28, 2007, which is incorporated in its entirety by reference as if fully set forth herein. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to an electronic medical device for implanting into a living body, and more particularly to the structure and method of manufacture of the device&#39;s outer housing for the purposes of enhancing the device&#39;s transcutaneous electromagnetic coupling to extracorporeal systems for the transfer of energy and/or information via telemetry. Such implantable devices include, without limitation, pacemakers; defibrillators; drug delivery pumps; cochlear implants; brain activity monitoring/stimulation systems (such as for sleep apnea and other sleep disorders, migraine headaches, epilepsy, depression, Alzheimer&#39;s, Parkinson&#39;s Disease, essential tremor, dementia, bipolar spectrum disorders, attention deficit disorder, stroke, cardiac disease, diabetes, cancer, eating disorders, and the like); implantable diagnostic devices used to monitor a patient&#39;s neurological condition, to determine, e.g., the patient&#39;s real-time susceptibility to a seizure for a time period. 
         [0004]    Many implantable medical electronic devices utilize an internal source of electrical energy to power the device electronics for the purposes of, for example, diagnostics and/or therapy. Additionally, many implantable devices require such a significant amount of power that it is necessary to utilize transcutaneous energy transmission (TET) from an extracorporeal source to an implanted receiver which is connected to a rechargeable battery. To date, one of the more efficient recharging means employs an external transmission coil and an internal receiver coil which are inductively coupled. In this TET approach, the external primary transmission coil is energized with alternating current (AC), producing a time varying magnetic field that passes through the patient&#39;s skin and induces a corresponding electromotive force in the internal secondary receiving coil. The voltage induced across the receiving coil may then be rectified and used to power the implanted device and/or charge a battery or other charge storage device. Additionally, many medical electronic devices rely on noninvasive telemetry in order to allow data and control signals to be bi-directionally communicated between the implanted medical device and an external device or system. Such telemetry can be accomplished via a radio frequency (RF) coupled system using a transmitting antenna to a receiving antenna by way of a radiated carrier signal, or by using the power transfer coils for data transmission. 
         [0005]    Electronic circuits and systems that are to be implanted in living organisms are hermetically packaged in a biocompatible material for the purposes of protecting the electronic circuitry from body fluids and protecting the organism from infection or other injury caused by the implanted materials. The most commonly used materials for implantable electronic devices are biocompatible metals, glass, and ceramics. Biocompatible metals include, for example without limitation, titanium, a titanium alloy, stainless steel, cobalt-chromium, platinum, niobium, tantalum, and various other possible alloys. Normally, metal enclosures consist of separate metal parts welded together to insure hermeticity. However, implant enclosures made of conductive metal present difficulties with respect to both transcutaneous energy transmission and telemetry. Specifically, the time varying magnetic charging field induces eddy currents within the metal housing and inhibits the magnetic flux as it passes through the case. With respect to RF telemetry from the implanted device to a receiver external to the patient, the metal case acts as a Faraday cage and tends to limit the rate of information transfer between the implanted device and the external system due to circulating eddy currents that absorb energy from the magnetic field and produce a magnetic field that opposes the incident magnetic field. The magnitude of the eddy currents is approximately proportional to the frequency of the AC magnetic field because the magnitude of the voltage induced within the conductive material is proportional to the time rate of change of magnetic flux as described in Faraday&#39;s Law, E=−dΦ/dt, where E is the induced voltage and Φ is the magnetic flux impinging on the material. The carrier frequency for telemetry is limited by the amount of eddy current attenuation that the system can tolerate. 
         [0006]    It is necessary to transmit significant amounts of power through the device case in order to recharge the device battery in a reasonable period of time. The implanted induction charging system typically uses a two-winding transformer with a non-ferrous (air) core. The energy transfer efficiency is approximately proportional to the number of turns in the transformer windings and the rate of change (frequency) of the alternating current, as follows: 
         [0000]    
       
      
       e 
       2 
       =M di 
       1 
       /dt+L 
       2  
       di 
       2 
       /dt  
      
     
         [0007]    Where e 2  is the voltage induced across the secondary winding, M is the mutual inductance of the primary and secondary windings, L 2  is the inductance of the secondary winding and di 1 /dt and di 2 /dt are the time rate of change (frequency) of the primary and secondary currents. 
         [0008]    Because the physical size of the implanted device limits the size and, hence, the inductance (L 2 ) of the receiving coil within the device, it is desirable to operate the inductive coupling system at the highest possible frequency in order to obtain the maximum coupling efficiency and energy transfer. Raising the operating frequency, however, increases the eddy current losses, so that the overall induction system efficiency is severely reduced. Additionally, such induced eddy currents create unwanted heat within the implantable enclosure. 
         [0009]    A number of approaches have been proposed to address the limitations of induced eddy currents upon a metallic medical device enclosure with respect to TET and telemetry systems: 
         [0010]    Ceramic Sleeve with a Metal Header. One approach is to utilize a deep drawn ceramic sleeve forming the majority of the enclosure body. The sleeve has a closed end, an open end for receiving electronic components and a metallic header for closing the open end (see U.S. Pat. No. 4,991,582.) Such a device, when implanted, has ceramic distal, proximal and side walls (relative to the skin) and an extracorporeal charging and/or telemetry device. This approach has, however, primarily been limited to small medical device enclosures (e.g., cochlear implants) due to the weight of the ceramic material. For larger devices such as an implantable pulse generator, the weight of the ceramic sleeve becomes a significant limitation due to the overall weight of the enclosure given the amount of ceramic used, the relatively large density of the ceramic, and the required large wall thickness (see also U.S. Pat. No. 6,411,854). 
         [0011]    Polymer Casing. Another approach is to avoid using both metal (problematic due to eddy currents) and ceramic (problematic due to weight) in favor of a biocompatible polymer material for the outer enclosure. This approach attempts to use epoxy to encapsulate the receiving coil, antenna, and a secondary enclosure and provide a hermetically sealed sub-housing for the system electronics. The polymer and/or epoxy material does not, however, provide for a true hermetic seal, as eventually body fluids migrate through the material and degrade the receiving coil and antenna. 
         [0012]    External Coil. In order to circumvent the problem of the metal housing material reducing the efficiency of the TET induction system efficiency, some devices have opted to place the receiving induction coil on the outside of the metal housing. This approach, however, increases both the size of the implant, the complexity of the surgical implant process, and the complexity of the device given the necessity for additional hermetic electrical feed-through connections between the secondary coil and the internal electronic circuitry. Additionally, the external coil would still have to be a biocompatible material as with the polymer casing approach above. 
         [0013]    Thin Metal Window. U.S. Pat. No. 7,174,212 presents an approach for increasing the efficiency of high speed/high carrier frequency telemetry via the use of (1) a metallic housing having a thin metal telemetry window having a thickness on the order of 0.005 inches and/or (2) a metal alloy (e.g., titanium alloy) window having reduced electrical conductivity parameters. However, as the window material still is made of an electrically conductive material (although reduced in thickness), this solution is non-ideal as an RF telemetry signal and/or a magnetic field will still induce eddy currents thereby reducing the efficiency of the telemetry link. 
         [0014]    Machined Grooves in Metal Casing. U.S. Pat. No. 5,913,881 presents an approach for increasing the efficiency of high speed/high carrier frequency telemetry by creating grooved recesses arranged on either or both sides of the implanted housing wall to reduce the overall thickness of the wall and to create discontinuities along the wall surface in order to reduce the conductivity of the metal housing wall, thereby decreasing the induced eddy currents and providing increased telemetry efficiency. 
         [0015]    Other hermetic housings for implantable medical devices are described in U.S. Pat. No. 4,785,827 and U.S. Pat. No. 5,876,424. 
         [0016]    Improved medical device structures and methods of manufacture are needed to overcome at least the shortcomings stated above. 
       SUMMARY OF THE INVENTION 
       [0017]    Described herein is a hermetically sealed implantable medical device housing having a construction permitting for efficient magnetic coupling and RF telemetry via a non-metal housing free path from the implantable device electronics to the remote charging and telemetry unit while also being relatively light weight. Additionally, this housing design allows for increased manufacturing efficiency and a more mechanically stable/robust housing to mount the internal electronic and mechanical components. 
         [0018]    One aspect provides an implantable medical device having a first housing component comprising a first material mated to a second housing component comprising a second material. The first housing component may be a ceramic housing component (formed, e.g., from zirconium oxide, aluminum oxide and/or boron nitride), and the second housing component may be a metal housing component (formed, e.g., from platinum, niobium, titanium, tantalum and/or alloys of these metals) attached to the ceramic housing component to form a hermetically sealed enclosure. An electronic trans-housing magnetic flux component may be disposed within the enclosure. In some embodiments, the electronic trans-housing magnetic flux component includes a telemetry transmission coil, and in some embodiments, the electronic trans-housing magnetic flux component includes an magnetic flux energy receiver coil. Some embodiments also have a metal weld ring brazed onto the ceramic housing component and welded onto the metal housing component. The ceramic housing component may have a wall thickness between about 0.06 inches and about 0.30 inches, and the metal housing component may have a wall thickness between about 0.01 inches and about 0.10 inches. In some embodiments, the implant may also have an electrode connector within the enclosure communicating with an opening in the metal housing component; and a ceramic component surrounding the opening. 
         [0019]    Another aspect provides an implantable medical device having a ceramic housing component (formed, e.g., from zirconium oxide, aluminum oxide and/or boron nitride); a metal housing component (formed, e.g., from platinum, niobium, titanium, tantalum and/or alloys of these metals); a circumferential sealing member attached to a periphery of the ceramic housing component and to a periphery of the metal housing component to form a hermetically sealed enclosure; and an electronic trans-housing magnetic flux component disposed within the enclosure. In some embodiments, the electronic trans-housing magnetic flux component includes a telemetry transmission coil, and in some embodiments, the electronic trans-housing magnetic flux component includes an magnetic flux energy receiver coil. The ceramic housing component may have a wall thickness between about 0.06 inches and about 0.30 inches, and the metal housing component may have a wall thickness between about 0.01 inches and about 0.10 inches. In some embodiments, the implant may also have an electrode connector disposed within the metal housing component, the electrode connector having a sealable opening communicating with the enclosure. The electrode connector may be made of ceramic. 
         [0020]    Still another aspect provides an implantable medical device having a first metal housing component (formed, e.g., from platinum, niobium, titanium, tantalum and/or alloys of these metals); a second metal housing component, the second metal housing component forming an opening; a ceramic housing component (formed, e.g., from zirconium oxide, aluminum oxide and/or boron nitride) disposed in the opening, the first metal housing component, the second metal housing component and the ceramic housing component cooperating to form a hermetically sealed enclosure; and an electronic trans-housing magnetic flux component disposed within the enclosure. In some embodiments, the electronic trans-housing magnetic flux component includes a telemetry transmission coil, and in some embodiments, the electronic trans-housing magnetic flux component includes an magnetic flux energy receiver coil. The ceramic housing component may have a wall thickness between about 0.06 inches and about 0.30 inches, and the first metal housing component may have a wall thickness between about 0.01 inches and about 0.10 inches. In some embodiments, the implant may also have an electrode connector disposed within the first metal housing component, the electrode connector having a sealable opening communicating with the enclosure. The electrode connector may be made of ceramic. 
         [0021]    Still another embodiment provides a clamshell type of housing having a pair of confronting concave components which when mated together form a perimeter parting line. This line forms a plane, which when implanted in the human body lies approximately parallel to the coronal plane. The distal concave component (relative to the patient&#39;s skin) is made of a biocompatible metal while the proximal concave component is made of a ceramic thereby allowing magnetic flux to pass through the proximal implant side to the extracorporeal charging device and/or telemetry unit. 
         [0022]    In yet another embodiment, a metallic enclosure is constructed having a ceramic window located on the proximal implant side relative to the patient skin and lies approximately parallel to the coronal plane in the human body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0024]      FIG. 1  is an exploded perspective view of an implantable medical device according to an embodiment of the invention. 
           [0025]      FIG. 2  is an exploded perspective view of an implantable medical device according to another embodiment of the invention. 
           [0026]      FIG. 3  is an exploded perspective view of an implantable medical device according to yet another embodiment of the invention. 
           [0027]      FIG. 4  shows the implantable medical device of  FIGS. 1 ,  2  or  3  implanted in a patient. 
           [0028]      FIG. 5  shows a cross-sectional view of an implanted medical device within a patient relative to the coronal plane of the patient. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1  is an exploded perspective view of a hermetically sealed implantable medical device according to one embodiment of the invention. The medical device housing includes ceramic housing component  10  which is made of ceramic material such as, for example without limitation, zirconium oxide, yttrium stabilized zirconium oxide, aluminum oxide, boron nitride, or other suitable material. When implanted, ceramic component  10  is disposed proximate the patient&#39;s skin, i.e., it is disposed between the portion of the patient&#39;s skin where an extracorporeal charging and/or telecommunication device will be positioned and the implanted trans-housing magnetic flux component(s), such as an implanted telemetry coil or battery charger coil (see e.g.,  FIG. 5 ). The ceramic proximal housing component  10  therefore allows magnetic flux associated with inductive charging and/or radio frequency/inductive telemetry to efficiently pass through the hermetically sealed enclosure proximal face without inducing eddy currents. 
         [0030]    In some embodiments the ceramic housing component has a wall thickness between about 0.03 inches and about 0.30 inches, and in some particular embodiments between about 0.06 inches and about 0.30 inches. 
         [0031]    The implantable medical device also includes metal housing component  80  made of a biocompatible metal (such as platinum, niobium, titanium, tantalum, or an alloys of one or more of these metals) that cooperates with the ceramic housing component  10  to form a hermetic enclosure. In this embodiment, metal housing component  80  is attached to ceramic housing component  10  with weld ring  20  which is brazed onto the ceramic housing component and welded onto the metal housing component using techniques known in the art. Weld ring  20  is made of a biocompatible metal material such as, for example without limitation, platinum, niobium, titanium and tantalum, or any alloy of one or more of these metals. When implanted, metal housing component  80  is oriented distal to the portion of the implanted trans-housing magnetic flux component(s), i.e., not between the portion of the patient&#39;s skin where an extracorporeal charging and/or telecommunication device will be positioned and the implanted trans-housing magnetic flux component(s) (see e.g.,  FIG. 5 ). 
         [0032]    In some embodiments the metal housing component has a wall thickness between about 0.01 inches and about 0.10 inches. 
         [0033]    In this embodiment, ceramic plate  90  is brazed within an opening in the metal housing component  80  to allow implanted diagnostic and/or therapeutic electrodes to be connected into the hermetically sealed enclosure. Plate  90  has sealable ferrule connectors  92  through which electrode leads may pass from the enclosure to the exterior of the implant housing. Metal header  100  is used to support and cover the electrode feed-through ferrule connectors  92 . Header  100  has one or more openings  102  which are configured to allow electrical leads to pass through the header from the enclosure to the exterior of the housing. When attached, header  100  cooperates with metal housing component  80  to complete the enclosure formed by the housing. Plate  90  may be formed from other biocompatible non-conductive materials as well. 
         [0034]    The mechanical and electrical components of the implantable medical device are placed within the enclosure prior to connecting the housing components. In this illustrated embodiment, the medical device components include secondary coil  30  which is used for receiving transcutaneously transferred energy from an extracorporeal primary coil charging device. Exemplary external devices that can be used to transfer energy (and/or data) to the medical device housings described herein can be found in co-pending U.S. patent application Ser. No. 12/180,996, filed Jul. 28, 2008, which is hereby incorporated by reference herein. Coil  30  is shown as a planar winding made from conductive traces on a printed circuit board. Alternative embodiments include discrete wire windings either in a planar geometry or a coil/bobbin geometry. Such discrete wire windings have highly conductive properties and may include silver wire, copper wire, copper magnetic wire, Litz wire, woven wire, gold alloy, or other suitable materials known in the art. Located behind (i.e., distal to) the winding is magnetic flux shield/diverter  40  which serves to provide a lower reluctance magnetic return to the primary coil thereby increasing the transfer of energy as well as shielding implantable electronics  50  from the large magnetic fields. The magnetic material of flux shield  40  generally has a high magnetic permeability, and may be, for example without limitation, ferrite, Metglas® (Metglas Inc, Conway, S.C., U.S.A), Mμ metal (Mμ Shield Co., Manchester, N.H., U.S.A), Wave-X™ (ARC Technologies, Inc. Amesbury, Mass., U.S.A.), or other suitable material. Spacer  35 , which in some embodiments in made of plastic, is disposed between coil  30  and magnetic flux shield/diverter  40  and serves to capture coil  30  and flux diverter  40  and maintain their spacing from electronics  50 . In some embodiments spacer  35  is an internal frame (or chassis) that mechanically locates/protects several of the internal components. Spacer  35  may additionally facilitate manufacturing by offering a basis for a stand-alone subassembly. For example, charge coil  30 , electronic components  50 , and/or other components can be mechanically affixed to spacer element  35  prior to installation inside the titanium-ceramic housing). 
         [0035]    The medical device implant electronics  50  are located on a board located behind (distal to) the magnetic flux shield/diverter  40 . The medical device implant electronics  50  may, e.g., control therapy and/or diagnostic processes of the implant. For example, the implant electronics may include a rectifier and a charging circuit which allows a coupled AC voltage to be converted to a DC voltage in order to charge implantable rechargeable battery  70 . The implant electronics may also include telemetry components to allow data and control signals to be bi-directionally communicated between the implanted medical device and an external device or system. This telemetry may be accomplished via an RF-coupled system using a transmitting antenna to a receiving antenna by way of a radiated carrier signal. Such antenna(s) within the implant may be located on the proximal side or below or above the magnetic shield  40  in order to insure the signals are not attenuated by the magnetic shield. An additional advantage of the distal placement of the metal housing component is the fact that this back conducting plate will enhance the projection of the radiating carrier signal towards the extracorporeal telemetry unit. 
         [0036]    Behind, or distal to, electronics board  50  is compliant liner  60  which houses rechargeable power source  70 . The rechargeable power source can be any of a variety of power sources including a chemically-based battery or a capacitor. Exemplary batteries include, without limitation, Lithium-ion (Li) and Li-polymer batteries which are examples of small and thin batteries. Alternative rechargeable batteries which may be used include, without limitation, lead-acid, Ni-iron, Ni-cadmium, Ni-Metal Hydride, Ni-zinc, Li-iron phosphate, Li-sulfur, Li-Nano Titanate, Zinc bromide, and other rechargeable batteries known in the art. 
         [0037]    In this embodiment, when ceramic housing component  10  and metal housing component  80  are mated together by welding distal metal housing  80  to weld ring  20  and brazing weld ring  20  onto ceramic housing  10 , the parting line between the two enclosure housings forms a plane.  FIG. 5  is a cross-sectional top view showing an exemplary embodiment of implanted medical device  300  in which this plane  302 , once the medical device is implanted in the human body, lies approximately parallel to the coronal plane “CP” of the human body. The proximal housing component  304  (e.g., ceramic housing component) faces outward towards the patient skin  308 , while the distal housing component  306  (e.g., distal housing component) is distal relative to the proximal housing component. External device  310  is positioned adjacent the skin and can transmit energy (and/or receive data) to implanted medical device  300 . In alternative embodiments, the medical device may be implanted within the patient at a location such that the plane formed by the parting line between two housing components is not parallel to the coronal plane. The plane will depend on where the medical device is implanted and for what purpose the medical device is implanted within the patient. 
         [0038]    Additionally, the plane formed by the parting line between two housing components is not always generally parallel to the patient&#39;s skin. The plane may be offset at an angle from the general plane of the skin, as long as the medical device enclosure is implanted in such an orientation that an external device can transmit power and/or data through the ceramic housing component (and/or receive data therethrough). 
         [0039]    This configuration provides for a light weight enclosure because the distal concave enclosure housing  80  is made of thin metal. This configuration also provides an enclosure which allows for the efficient transmission of magnetic flux to the extracorporeal charging device and telemetry unit via the proximal ceramic housing component  10 . 
         [0040]    Finally, the medical implant housing of this embodiment has additional advantages over a deep drawn ceramic implant housing having a metallic header. For example, this embodiment provides a simplified manufacturing processes as well as a more robust design. As illustrated in  FIG. 1 , the housing and the electronic and mechanical components are all amenable to top-down assembly processes as compared to the metal header deep drawn ceramic enclosure. Additionally, as the back (i.e., distal) side of the enclosure is metal, electronic and mechanical components can be mounted against the metallic housing component. In the deep drawn ceramic enclosure, on the other hand, all of the mechanical and electronic components are mounted to the metal header which presents a more challenging assembly and creates a long lever in which significant amount of moment of inertia may be created. 
         [0041]      FIG. 2  illustrates an alternative embodiment of the medical device housing shown in  FIG. 1  that reduces or eliminates the concavity of the housing components. Wide metal band  65  around the outer perimeter of the housing spans the distance between the edge of ceramic housing component  10  and metal housing component  85 . Band  65  cooperates with housing components  10 ,  85  and  100  to form a hermetic enclosure for the implant&#39;s components. This embodiment may permit the housing to be lighter due to a reduction in the amount of ceramic used to form the housing. 
         [0042]      FIG. 3  illustrates an alternative embodiment which represents a lighter weight device, in which proximal ceramic housing  10  of  FIG. 1  is replaced with proximal biocompatible metal housing component  110 . A ceramic window  120  is disposed in an opening in the metal housing component  110  which allows for the magnetic flux associated with inductively coupled charging and/or radio frequency telemetry to efficiently pass through the hermetically sealed enclosure proximal face without inducing eddy currents. The ceramic window  120  can be brazed onto the proximal biocompatible metal housing  110  prior to the installation of the implant electronics and hardware  30 ,  40 ,  50 ,  60  and  70 . Next, the proximal metal housing component  110 , which is coupled to ceramic window  120 , and the distal metal housing component  80  are welded together. Many of the other elements of the medical device described in alternative embodiments herein can be incorporated into the embodiment shown in  FIG. 3 . 
         [0043]    When the medical device from  FIG. 3  is implanted in a patient, the proximal metal housing and ceramic window assembly are disposed closer to the skin than the distal housing component (as is proximal portion  304  shown in  FIG. 5 ). 
         [0044]      FIG. 4  illustrates exemplary implantable medical device  208  located in the patient  200 . Electronic lead  206  is attached to the medical device and attached to electrode arrays  204 . In this example the electrode arrays  204  are implanted intracranially and the cable(s)  206  is tunneled beneath the skin through the neck to the implanted medical device  208  that is implanted in a subclavicular cavity of the subject. Note however, that  FIG. 4  is only shown as an example and the medical device implant is not limited to the subclavicular cavity, as it could be also located intracranially or any other place within the body. Similarly, the medical device is not limited to requiring electrodes placement within the intracranial cavity or requiring such electrodes at all. 
         [0045]    An extracorporeal device  210  may be used as described herein to transfer energy and/or information via telemetry to device  208  across the patient&#39;s skin. To that end, device  208  is oriented within the patient so that a ceramic housing component is closer to the skin where extracorporeal device is positioned than is a metal housing component.