Abstract:
An implantable system and method for deep brain stimulation (DBS) treatments. The implantable system is sufficiently small and self-contained to enable implantation of the entire system within the brain, or optionally within the brain and the surrounding tissue. The system comprises an implantable inductor on which a voltage is induced when subjected to an electromagnetic field, and an implantable device comprising a housing, stimulating elements at an exterior surface of the housing, and electronics within the housing and electrically connected to the implantable inductor. The electronics produces a brain-stimulating current from the voltage induced on the implantable inductor and then delivers the brain-stimulating current to the stimulating elements. Deep brain stimulation is performed by subjecting the inductor to an electromagnetic field to induce a voltage on the inductor that powers the electronics to produce and deliver the brain-stimulating current to the stimulating elements.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/999,397, filed Oct. 18, 2007, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to systems, devices and methods for a medical treatment known as deep brain stimulation (DBS). More particularly, the present invention relates to a miniature implantable DBS device capable of being entirely implanted within the brain and optionally the surrounding tissue. 
         [0003]    DBS methods are used to stimulate the brain with electrical impulses to treat a variety of brain conditions and diseases, including but not limited to depression, Parkinson, stroke, essential tremor, dystonia, and tremor due to multiple sclerosis. DBS involves surgically implanting electrodes within the brain and then operating the electrodes to deliver electrical impulses capable of blocking certain activities in the brain, and particularly abnormal activity believed to cause undesirable conditions and symptoms. Programming of the deep brain stimulation treatment is easy and painless, and can offer patients relief from tremors, rigidity, slowness of movement, and stiffness, and may treat balance problems associated with their conditions. The level and duration of stimulation can be adjusted as a patient&#39;s condition changes over time. 
         [0004]    DBS devices typically comprise a very thin insulated wire lead terminated with four electrode contacts. The lead is routed out of the skull through a small opening and connected to an extension wire subcutaneously routed along the head, neck, and shoulder to an impulse generator or other suitable neurostimulator device implanted under the skin, for example, in the chest area. As such, conventional DBS procedures and devices require two surgical procedures: a surgical procedure to implant the electrodes within the brain, and a second surgical procedure to implant the neurostimulator device in the chest. 
         [0005]    The success of DBS is directly related to finding the specific area in the brain for stimulation. Consequently, during the brain surgery portion of the procedure the patient is only given a local anesthetic to numb the area to be operated on, and the patient remains awake and alert so that the surgeon can talk to the patient to ensure the proper areas of the brain are identified for stimulation. While the patient&#39;s head is immobilized with a special frame, two holes are drilled in the skull and, guided by imaging techniques, the surgeon implants electrodes to precisely targeted areas on each side of the brain. A neurologist and a neurosurgeon usually decide whether to target one of two areas commonly stimulated by DBS: either the subthalamic nucleus (STN) or the internal globus pallidus (GPi). These structures are deep within the brain and involved in motor control, and stimulation of these areas appears to block the signals that cause the disabling motor symptoms of the disease. 
         [0006]    After the electrodes have been properly placed, the second surgical procedure is performed by which the surgeon implants the neurostimulator in the patient&#39;s chest, and the extension wire is routed beneath the patient&#39;s skin and connected to the electrode leads and the neurostimulator. Depending on the type of neurostimulator selected, two neurostimulators may be implanted to control symptoms affecting both sides of the body. Implantation of the neurostimulator is usually performed while the patient is under general anesthesia. Deep brain stimulation patients are often in the hospital for several days, and stimulation is usually initiated for the first time within a few weeks after implantation. The neurostimulator, which is usually battery powered, is programmed from outside the body to deliver a prescribed and usually continuous dosage of electrical impulses customized to the individual. 
         [0007]    Because deep brain stimulation involves brain surgery, it can be appreciated that DBS procedures entail certain risks. The neurostimulator can also pose undesirable risks and side effects, due in part to the size of the neurostimulator. For example, an existing commercial unit used to control Parkinson&#39;s disease symptoms is about 7.5 cm wide and 1.3 cm thick, and contains a small battery and computer chip. Finally, there can be inconveniences associated with deep brain stimulation, including battery replacement and hardware malfunctions. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The present invention provides an implantable system and method suitable for DBS treatments. The implantable DBS system is sufficiently small and self-contained to enable implantation of the entire DBS system within the brain, or optionally within the brain and the surrounding tissue. The DBS system can be implanted by a simple outpatient procedure, and therefore avoids the prior requirement for placing a patient under general anesthesia. 
         [0009]    According to a first aspect of the invention, the system comprises an implantable inductor on which a voltage is induced when subjected to an electromagnetic field, and an implantable device comprising a housing, stimulating elements at an exterior surface of the housing, and electronics within the housing and electrically connected to the implantable inductor. The electronics produces a brain-stimulating current from the voltage induced on the implantable inductor and then delivers the brain-stimulating current to the stimulating elements. According to another aspect of the invention, deep brain stimulation is performed by implanting the inductor and device so that the device is within the brain, and then subjecting the inductor to an electromagnetic field to induce a voltage on the inductor that powers the electronics to produce and deliver the brain-stimulating current to the stimulating elements. 
         [0010]    Significant advantages of this invention include the miniature size of the DBS device, simpler delivery and implantation (via an outpatient procedure and/or catheter delivery), and lower risks from the implantation procedure. Other advantages can include batteryless operation, reduced risks associated with side effects, additional functionality (for example, measurement of intracranial pressure (ICP), pH, neuro activities, or other physiological parameters), multiple stimulating probes at the same or different parts of the brain, and wireless communication. 
         [0011]    Other objects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  represents a plan view of deep brain stimulation electrodes arranged on a surface of an implantable device in accordance with an embodiment of this invention. 
           [0013]      FIGS. 2 through 6  represent various embodiments for implantable deep brain stimulation devices in accordance with embodiments of this invention. 
           [0014]      FIGS. 7 and 8  represent examples of intracranial placement of implantable deep brain stimulation devices of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention comprises a miniature implantable device and method for deep brain stimulation. The device contains all elements typically found in existing deep brain stimulation systems, including but not limited to neuro-leads (for example, pads, contacts, electrodes, etc.) and a neurostimulator. In contrast to existing deep brain stimulation systems, the device does not require a separate extension or neurostimulator that must be separately implanted. As such, the miniature integration achieved with the device avoids complications associated with prior art deep brain stimulation systems. The invention will be described in reference to embodiments of the invention depicted in  FIGS. 1 through 8 , in which consistent reference numbers are used to identify functionally similar structures. 
         [0016]      FIG. 1  represents a plan view of an embodiment in which two brain-stimulating elements  12  (neural leads, pads, contacts, electrodes, etc.) are located on an outer surface  14  of a deep brain stimulation (DBS) device  10 . The device  10 , for example, any one of the embodiments shown in  FIGS. 2 through 8 , is capable of generating and delivering an electric current to the stimulating elements  12 , for example, at levels consistent with prior art DBS systems. As shown in  FIGS. 2 through 8 , other electrode configurations can also be utilized and such variations in electrode configurations are intended to be encompassed by this invention. The stimulating elements  12  can be formed on the device surface  14  using a variety of processes, including deposition by electroplating, printing, or another process known in the art. The stimulating elements  12  can be formed to define a small gap therebetween, for example, about 0.1 to about 1000 micrometers. The stimulating elements  12  should be resistant to corrosion in the cerebral spinal fluid (CSF) within and surrounding the brain. For this reason, platinum, palladium, silver, titanium, and iridium alloys and silver oxide are believed to be well suited as materials for the stimulating elements  12 . The stimulating elements  12  can also be passivated with a thin dielectric corrosion resistant layer. 
         [0017]    As evident from  FIGS. 2 and 3 , the stimulating elements  12  may have a variety of configurations, including two-dimensional structures (for example, flat pads or contacts) as shown in  FIG. 2 , and three-dimensional structures (for example, probes, etc.) that protrude from the device surface  14  as shown in  FIG. 3 . The stimulating elements  12  are connected to a coil assembly  22  (with an optional core) and electronics  24  (for example, printed circuit boards (PCBs), application-specific integrated circuits (ASICs), capacitor, diode, and/or other electrical components) within the device housing  20 . The device  10  is preferably coupled via the coil assembly  22  to an external readout unit (not shown) capable of wirelessly providing radio frequency (RF) power to the device  10  and its electronics  24 . The device  10  may further include a charge-storing device, such as capacitor or rechargeable battery capable of being charged and then discharged to provide the desired electric stimulating pulse. As such, the device  10  may contain a battery or may be batteryless. 
         [0018]    The exterior of the device housing  20  can have a wide variety of configurations, including cylindrical exterior shapes as shown in  FIGS. 2 and 3 , as well as disk and planar exterior shapes. The housing  20  is preferably rigid and may be formed of a discrete component, such as a cylindrical glass tube or a coin-shape container with a hollow interior. Alternatively, the housing  20  may be defined by potting the components of the device  10  together using a suitable biocompatible potting material, such as an epoxy. Depending on its construction, the housing  20  can be made from a variety of other biocompatible materials, including ceramics, polymers, silicone, Parylene, etc. 
         [0019]    In  FIGS. 2 and 3 , the DBS device  10  is represented as a sealed cylindrical-shaped capsule having a hollow interior in which the coil assembly  22  and electronics  24  are hermetically enclosed, with only the stimulating elements  12  exposed at the external surface  14  of the housing  20 . The stimulating elements  12  are shown as located at the end of the cylindrical-shaped housing  20 , though it is foreseeable that the stimulating elements  12  could be located elsewhere, for example, along the sides of the housing  20 . The stimulating elements  12  and possibly some of the electronics  24  may be mounted on a substrate, connected together using various methods known in the art, for example, wirebonding, flexible connectors, etc., or potted together using a biocompatible epoxy or any other suitable potting material. The device surface  14  at which the stimulating elements  12  are disposed can be either rigid or flexible substrate material, or a combination (for example, a rigid-flex substrate, where part of the substrate is rigid and another part is flexible). In the case of flexible substrates, various polymers, Parylene, silicone, or other biocompatible flexible material may be used. In the case of rigid substrates, glass, silicon, ceramics, carbides, alloys, metals, hard polymers, Teflon, are some examples, although other types of materials can also be used. In the case of rigid-flex substrates, the rigid and flexible parts may be made from dissimilar material. The stimulating elements  12  themselves, especially three-dimensional stimulating elements  12 , can also either be rigid, flexible, or a combination. For example the stimulating elements  12  can be formed by a flexible three-dimensional element made from polymers, Parylene, silicone, etc., which is partially or fully metallized. The stimulating elements  12  may also have a flexible tip portion connected to a rigid portion connected to the device surface  14 , or alternatively may have a rigid tip portion connected to the surface  14  via a flexible portion. The rigid and flexible portions may be made from similar or dissimilar materials. 
         [0020]    In some cases, it may be desirable to apply additional materials (organic, metal, or biocompatible material) to the exterior of the housing  20  to protect certain regions of the DBS device  10 . For example, a coating may be applied to all but the stimulating elements  12 , or the stimulating elements  12  may be coated with a material that differs from the material applied to the remainder of the housing  20 . Examples of suitable coating materials include polymers, Parylene, silicone, hydrogels, titanium, nitrides, oxides, carbides, silicides, etc. 
         [0021]    The coil assembly  22  can be made using any method known in the art, such as winding a conductor around a ferrite core as represented in  FIGS. 2 through 4  and  8 , depositing (electroplating, sputtering, evaporating, screen printing, etc.) a conductive coil (preferably made from a highly conductive metal such as silver, copper, gold, etc.) on a rigid or flexible substrate  28  as represented in  FIGS. 5 through 7 ), or any other method known to those skilled in the art. As such, the coil assembly  22  can be either flat or three-dimensional (cylindrical, cubic, etc.). An advantage of a flat coil configuration is that it can be easily implanted under the scalp such that the coil assembly  22  lies flat against the skull, as evident from FIG.  7 . 
         [0022]    The operation of the DBS device  10  can make use of a combination of powering and/or charging techniques and devices, including but not limited to wireless powering, one or more rechargeable or primary batteries, one or more capacitors, and/or one or more super capacitors. In a preferred embodiment, the device  10  employs a communication/telepowering scheme based on magnetic telemetry. Such schemes are disclosed in commonly-assigned U.S. Pat. Nos. 6,926,670 and 6,968,734 to Rich et al., whose contents are incorporated herein by reference. With such magnetic telemetry schemes, the device  10  preferably lacks an internal means for powering itself, and therefore lies passive in the absence of an external powering unit. When stimulation is desired, an external readout unit is brought within a suitable range of the device  10 , and an inductor within the readout unit transmits an alternating electromagnetic (RF) field to the coil assembly  22  of the device  10  to induce a voltage capable of powering the device  10 , as well as generate the brain-stimulating current for use by the stimulating elements  12 . When sufficient voltage has been induced in the coil assembly  22 , a supply regulator (rectification) circuitry within the electronics  24  of the device  10  converts the alternating voltage on the coil assembly  22  to a direct voltage that can be used by the electronics  24  as a power supply for signal conversion and communication, as well as deliver current to the stimulating elements  12  at an appropriate level for brain stimulation. At this point the DBS device  10  can be considered alert and may immediately deliver the brain-stimulating current to the elements  12  to initiate deep brain stimulation, or may await further commands from the readout unit prior to initiating deep brain stimulation. The readout unit may transmit either a continuous level of RF power to supply the device  10  with needed energy, or the readout unit may pulse the power allowing temporary storage in a battery or capacitor device within the device  10 . The device  10  may work/stimulate continuously, or may do so periodically. In a periodic stimulation, one embodiment includes one phase for charging one or more charge-storing devices (such as capacitors, rechargeable batteries, etc.) and another phase for stimulating the brain. The charging and stimulating phases of the device operation may overlap. 
         [0023]    As those skilled in magnetic telemetry are aware, a number of modulation schemes are available for transmitting data via magnetic coupling. Particularly suitable schemes include but are not limited to amplitude modulation, frequency modulation, frequency shift keying, phase shift keying, and also spread spectrum techniques. A preferred modulation scheme may be determined by the specifications of an individual application, and is not intended to be limited under this invention. In addition, many technologies exist that allow the device  10  to communicate signals to the readout unit via the coil assembly  22  or a second coil dedicated to signal transmission. Such signals can contain information obtained with the device  10 , such as pressure, flow, pH, CO 2  levels, neuron activities, etc. The device  10  may transmit to the readout unit at any interval in time, delayed or instantaneous, during readout RF transmission or alternately in the absence of readout transmission. 
         [0024]    In view of the above, the readout unit may further include signal reception, signal processing, and transmission circuitry for data analysis and subsequent communication. There are many techniques for construction of the readout coil and processing electronics known to those skilled in the art. The readout unit may interface to a display, computer, or other data logging device. In a preferred embodiment of the invention, the readout unit receives data from the DBS device  10  using the 13.56 MHz ISM band. Two modes of operation can be employed: (1) a data-logging measurement mode with optional data rates of, for example, 1 Hz and below, and (2) a real-time dynamic measurement mode with data rates of, for example, 100 to 500 Hz, for compliance and impulse tests. The readout unit may comprise analog RF front end electronics providing processing and user interface capabilities. A graphical user interface program can be used to control information (e.g., ICP monitor) and created in, for example, the LabVIEW and C visual programming languages. 
         [0025]    The external readout unit can be adapted to perform one or more of the following: remote monitoring of patients, including but not limited to home monitoring; monitoring of patients with telephone-based (or similar method) data and information delivery; monitoring of patients with wireless telephone-based (or similar method) data and information delivery; monitoring of patients with web-based (or similar method) data and information delivery; closed-loop drug delivery to treat diseases; warning systems for critical worsening of diseases and related conditions; portable or ambulatory monitoring or diagnostic systems; battery-operation capability; data storage; reporting global positioning coordinates for emergency applications; communication with other medical devices including but not limited to pacemakers, defibrillator, implantable cardioverter defibrillator, implantable drug delivery systems, non-implantable drug delivery systems, and wireless medical management systems. 
         [0026]      FIG. 4  is similar to  FIGS. 2 and 3 , but show the inclusion of a second element  26 , which may be another sensing element adapted to sense a physiological parameter or an actuating element adapted to physically induce, stimulate, or respond to conditions within the brain or the cerebral spinal fluid. As nonlimiting examples, the DBS device  10  can further incorporate various other miniature sensing elements adapted to detect and/or monitor various physiological parameters of a patient, such as intracranial pressure (ICP), temperature, flow, velocity, vibration, acceleration, and/or measure specific chemistries such as gas content (e.g., O 2  and CO 2 ), and/or may incorporate various miniature actuators, including but not limited to thermal generators, voltage sources, current sources, probes, electrodes, drug delivery pumps, valves, meters, microtools for localized surgical procedures, and radiation emitting sources. Various specific examples of these types of miniature sensors and actuators are known to those skilled in the art, and any one or more of these can be utilized in the DBS device  10  of the present invention if capable of sufficiently small size to permit placement of the DBS device  10  within a catheter for delivery and implantation, or otherwise permit noninvasive surgical implantation. A particular example is to incorporate a pressure sensor into the device  10  for patients with traumatic brain injury to monitor brain pressure and allow for tailoring of the DBS treatment with the device  10 . By measuring different physiologic parameters, the device  10  can use the measured physiologic parameter(s) to control, adjust or manipulate the stimulating function (for example, patter, frequency, location, amplitude, etc.). This approach allows dynamic and smart stimulation and allows the implementation of a closed-loop system. For example, if the second element  26  senses flow, the DBS device  10  can operate with other implanted or non-implanted devices (such as sensors, actuators, valves, etc.) as part of a closed-loop control system which can stimulate, monitor, measure one or more physiological parameter, and perform additional actions all based on feedback from one or more of other units in the closed-loop control system. 
         [0027]      FIGS. 5 and 6  represent DBS devices  10  configured so that the housing  20  contains the stimulating elements  12 , electronics  24 , etc., and is adapted for deep implantation within the brain, whereas the coil assembly  22  is fabricated on a flexible or rigid film  28  that can be located remote from the device  10 . The film  28  can be formed of any suitable biocompatible material, and is physically and electrically interconnected with the implantable housing  20  by a cable  30 . The connection provided by the cable  30  may be flexible, rigid, or combination of flexible and rigid. The cable  30  may be coated, potted or covered with a biocompatible material.  FIG. 6  differs from  FIG. 5  by the inclusion of the second element  26 , similar to  FIG. 4 . 
         [0028]      FIGS. 7 and 8  show DBS devices  10  of this invention comprising separate implantable housing and coil subassemblies, similar to  FIGS. 5 and 6 . In  FIG. 8 , the device  10  and its housing  20  are potted or coated, leaving only the stimulating elements  12  (not shown) in contact with the brain environment. The housing  20  is shown as having a conical distal tip to avoid snagging of vessels during insertion into the brain. In addition, the embodiment of  FIG. 8  is provided with a cylindrical-shaped coil assembly  22  similar to the coil assemblies  22  of  FIGS. 2 through 4 . The coil assembly  22  (and any packaging thereof) can be attached to the skull and placed under the scalp, or attached under the skull above the dura mater such that it does not pierce the dura, or placed outside the body (for example, attached on top of the scalp). An advantage of the device configurations of  FIGS. 5 through 8  is the ability for a very small footprint for the implanted portion of the DBS device  10  within the brain, while the bulkier coil assembly  22  is placed at a separate and possibly more favorable location. Other configurations are also foreseeable in which the brain stimulating elements  12  and possibly the electronics  24  of the DBS device  10  define an implantable subassembly, and the remaining components (including the coil assembly  22 , some electronics, and possibly a battery or another charge-storing device) define a second subassembly that is attached at the scalp surface, and the two subassemblies are physically and electrically connected together with the cable  30 . 
         [0029]    Anchoring provisions may be incorporated directly into the housing  20 , or added to the housing  20  by additional assembly steps. For example, the DBS device  10  could be inserted into a molded plastic or metal shell that incorporates anchoring provisions. Various other anchoring features and fasteners known in the art could also be used, including those adapted to attach to the skull or scalp using wires, screws (helical or otherwise), bolts, mesh, stents, springs, stitches, expandable tines, etc. Suitable anchoring mechanisms can also form part of another device with which the device  10  is implanted. For example, in patients with hydrocephalus, the anchoring mechanism can be part of the shunt used for draining the excess fluid. Suitable materials for anchors used with the device  10  include, but not limited to, Nitinol, Teflon, Parylene, polymers and metals. 
         [0030]    According to a particularly desirable aspect of the invention, the device  10  is sufficiently small and self-contained to allow implantation using a surgical procedure or a minimally-invasive outpatient technique. A nonlimiting example of an exterior size for the housing  20  is about one-half centimeter in width/diameter and about one or two centimeters in length. The insertion and placement of the device  10  into the brain can be a relatively simple procedure and done by a trained technician rather than a highly specialized surgeon. This aspect of the invention is an important advantage over existing deep brain stimulation devices that require two surgical procedures: surgery on the brain to implant electrodes, and surgery on the chest under general anesthesia to implant a neurostimulator device. 
         [0031]    In all applications, multiple DBS devices  10  may be used, either in close proximity or in separate locations. The multiple devices  10  may each be a completely separate unit and not share any common elements, or share a common coil assembly  22  or other device component. In some cases, the devices  10  may include or be used with multiple stimulating elements  12  on either the same or multiple different substrates. 
         [0032]    The device  10  can be used in the treatment of many different diseases, including but not limited to cardiovascular disease, depression, Parkinson&#39;s disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS, often referred to as “Lou Gehrig&#39;s disease”) Alzheimer&#39;s, borderline personality, compulsive disorders, addictions, stroke, brain trauma, brain injury, inflammation in the brain, tumors, hydrocephalus, cerebral palsy, essential tremor, coma, mental retardation, dystonia, and tremor due to multiple sclerosis. The device  10  can significantly improve the tailored treatment of many severe diseases as a result of offering an easy to use and relatively low-cost option for performing non-invasive, realtime, detailed and chronic monitoring/stimulation at home, in the doctor&#39;s office, or in the hospital. In addition to the deep brain stimulation, implantable devices similar to the device  10  of this invention could also be used for different internal organs, including but not limited to the heart, kidneys, lungs, bladder, and abdomen. 
         [0033]    While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the device  10  could differ from that shown, and materials and processes other than those noted could be used. Therefore, the scope of the invention is to be limited only by the following claims.