Abstract:
An implantable wireless lead includes an enclosure, the enclosure housing: one or more electrodes configured to apply one or more electrical pulses to a neural tissue; a first antenna configured to: receive, from a second antenna and through electrical radiative coupling, an input signal containing electrical energy, the second antenna being physically separate from the implantable neural stimulator lead; one or more circuits electrically connected to the first antenna, the circuits configured to: create the one or more electrical pulses suitable for stimulation of the neural tissue using the electrical energy contained in the input signal; and supply the one or more electrical pulses to the one or more electrodes, wherein the enclosure is shaped and arranged for delivery into a subject&#39;s body through an introducer or a needle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT application PCT/US2012/03220, international filing date Apr. 4, 2012, which claims the benefit of U.S. Provisional Patent Application 61/471,496, filed Apr. 4, 2011, which is hereby incorporated by reference in its entirely 
     
    
     TECHNICAL FIELD 
       [0002]    This description is related to implantable neural stimulators. 
       BACKGROUND 
       [0003]    A variety of therapeutic intra-body electrical stimulation techniques can treat neuropathic conditions. These techniques may utilize a subcutaneous battery operated implantable pulse generator (IPG) connected to one or more implantable wired leads. These leads have numerous failure modes, including mechanical dislodgement, impingement of the lead-extension tubing, infection, and uncomfortable irritation from the IPG and extension tubing. Various types of spinal cord stimulation (SCS) leads have been used to provide therapeutic pain relief. These lead configurations often include cylindrical percutaneous leads and paddle lead form factors. Cylindrical percutaneous leads typically have diameters in the range of 1.3 mm and contain a number of circular electrodes used for effectiveness testing during a trial implant period, and in many cases for the permanent implantation. Paddle leads, however, contain electrodes with a greater surface area directionally targeted for control over the excitation of the nerve bundles and may require surgical laminotomy. 
       SUMMARY 
       [0004]    Some embodiments provide an implantable neural stimulator wireless lead. The wireless lead includes: an enclosure; the enclosure housing; a) one or more electrodes configured to apply one or more electrical pulses to a neural tissue; b) a first antenna configured to receive, from a second antenna through electrical radiative coupling, an input signal containing electrical energy, the second antenna being physically separate from the implantable neural stimulator lead; c) one or more circuits electrically connected to the first antenna, the circuits configured to create the one or more electrical pulses suitable for stimulation of the neural tissue using the electrical energy contained in the input signal, and supply the one or more electrical pulses to the one or more electrodes, wherein the enclosure is shaped and arranged for delivery into a subject&#39;s body through an introducer or a needle. 
         [0005]    Embodiments may include one or more features. For example, a portion of the enclosure may leave the electrodes in a non-direct contact with the neural tissue after the lead has been delivered into the subject&#39;s body. The enclosure can be semi-cylindrical in shape and the electrodes may include at least one directional electrode that directs a current path associated with the one or more electrical pulses to a direction that is substantially perpendicular to the neural tissue. The electrodes may include a semi-cylindrical array of electrodes. The electrodes may be made of at least one of: platinum, platinum-iridium, gallium-nitride, titanium-nitride, iridium-oxide, or combinations thereof. The electrodes can include two to sixteen electrodes, each having a longitudinal length between 1.0 and 6.0 mm and a width between 0.4 and 3.0 mm. The electrodes are spaced between 1 mm to 6 mm apart and have a combined surface area of between 0.8 mm 2  to 60.00 mm 2 . 
         [0006]    The lead may be a paddle-style lead. Specifically, the lead can be a paddle lead with a height between 1.3 mm and 2.0 mm, and a width between 2.0 mm and 4.0 mm. The lead can be shaped concavely to secure a lateral position on the neural tissue after the lead has been delivered into the subject&#39;s body. The lateral position may be with regard to a dorsal aspect of the subject&#39;s spinal cord. For example, the lead has a concave profile between 1.0 mm and 1.5 mm, and a concave edge between 0.2 mm and 0.3 mm. 
         [0007]    The lead can be delivered into an epidual space of a subject&#39;s body. The delivery can be through a needle, such as, for example, a tuohy needle, no larger than gauge 14. The lead may be delivered to treat a neural tissue associated with the spinal column. 
         [0008]    The enclosure can further house a lumen to operate a navigating stylet during delivery of the enclosure. The enclosure may further include a distal tip. The distal tip can be rounded with a length of between 0.5 mm and 2.0 mm. The distal tip can also be pointed with a length of between 2.0 and 6.0 mm. The enclosure may have an external coating of bio-compatible polymer, the polymer includes at least one of: polymethymethacrylate (PMMA), polydimethylsiloxane (PDMS), parylene, polyurethance, polytetrafluoroethylene (PTFE), or polycarbonate. The enclosure may further have an external coating of silicone elastomer. The enclosure can further house antenna coupling contacts, the antenna contacts being electrically connected to the antennas and the circuit and configured to couple the antenna with the surrounding tissue. The antenna coupling contacts can include two to eight antenna-coupling pairs. The antenna coupling contacts may be located proximal, relative to the electrodes, in the enclosure. The antenna coupling contacts can each have a longitudinal length of between 1.0 mm and 6.0 mm, and a width of between 1.0 mm to 2.5 mm. The antenna coupling contacts can be spaced between 30 mm and 80 mm apart. At least one of the antennas can be constructed as a conductive trace contained on one of the circuits. At least one of the antennas can be fabricated as a conductive wire connected to one of the circuits. The circuits can be flexible circuits. The flexible circuits are capable of undergoing a bend radius of under 0.5 mm. The flexible circuits can be placed proximal, relative to the electrodes, in the enclosure. The flexible circuits can include a waveform conditioning circuit. 
         [0009]    Some embodiments provide a method of treating neurological pain. The method includes: providing an implantable neural stimulator lead including an enclosure that houses: one or more electrodes; a first antenna configured to receive, from a second antenna and through electrical radiative coupling, an input signal containing electrical energy, the second antenna being physically separate from the implantable neural stimulator lead; one or more flexible circuits electrically connected to the first antenna, the flexible circuits configured to: create the one or more electrical pulses suitable to be applied at the electrodes using the electrical energy contained in the input signal; and supply the one or more electrical pulses to the one or more electrodes, and implanting the neural stimulator lead into a subject&#39;s body through an introducer or a needle. 
         [0010]    Embodiments may include one or more of the following features. For example, a portion of the enclosure may leave the electrodes in a non-direct contact with a neural tissue after the lead has been implanted into the subject&#39;s body. The electrodes can include at least one directional electrode that confines a current path associated with the one or more electrical pulses in a direction substantially perpendicular to the neural tissue. The needle can be a tuohy needle no larger than gauge 14. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  illustrates two wireless paddle leads being implanted through an introducer into the epidural space. 
           [0012]      FIG. 2  illustrates a wireless paddle lead being implanted through an introducer into a human body. 
           [0013]      FIG. 3  illustrates a wireless paddle lead in place against the dura of the spinal cord. 
           [0014]      FIG. 4A  illustrates an example of an introducer. 
           [0015]      FIG. 4B  shows a cross-sectional view of the introducer illustrated in  FIG. 4A . 
           [0016]      FIG. 5A  illustrates another example of an introducer. 
           [0017]      FIG. 5B  shows a cross-sectional view of the introducer illustrated in  FIG. 5A . 
           [0018]      FIG. 6A  illustrates the distal tip of a wireless paddle lead. 
           [0019]      FIG. 6B  shows cross-sectional views of the distal ends of three embodiments of a wireless paddle lead. 
           [0020]      FIGS. 7A and 7B  respectively illustrate the dorsal and ventral sides of an embodiment of a wireless paddle lead. 
           [0021]      FIG. 7C  illustrates the ventral side of another embodiment of the wireless paddle lead. 
           [0022]      FIG. 8  illustrates an embodiment of a cylindrical and a semi-cylindrical wireless lead being placed in the epidural space using a needle. 
           [0023]      FIG. 9  illustrates an example of a cylindrical or semi-cylindrical wireless lead being implanted in the epidural space using a needle. 
           [0024]      FIG. 10  illustrates a cylindrical or semi-cylindrical wireless lead placed against the dura in the spinal column. 
           [0025]      FIG. 11A-11C  illustrate cross-sectional views of a semi-cylindrical lead, a cylindrical lead, and a paddle lead, respectively, while those leads are placed against the dura. 
           [0026]      FIGS. 12A-12B  illustrate perspective and profile views, respectively, of an embodiment of a wireless semi-cylindrical lead. 
           [0027]      FIG. 13A-13C  variously illustrate the electronic components included in two embodiments of the wireless lead. 
           [0028]      FIG. 14A-14B  illustrate a cross-sectional view of a fully cylindrical wireless lead or a semi-cylindrical wireless lead. 
           [0029]      FIG. 14C  illustrates a cross-sectional view towards the distal end of a semi-cylindrical wireless lead. 
           [0030]      FIG. 15  illustrates an embodiment of a cylindrical wireless lead. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Spinal cord stimulation may treat chronic neuropathic pain, especially low back pain and radiculopathy, vascular insufficiency in the feet or hands, angina, and more. In various implementations, a neural stimulation system can send electrical stimulation to targeted nerve tissue with neither cables nor inductive coupling to power the passive implanted stimulator. This can be used to treat pain or a variety of other modalities. The targeted nerve tissues may be, for example, in the spinal column including the spinothalamic tracts, dorsal horn, dorsal root ganglia, dorsal roots, dorsal column fibers, and peripheral nerves bundles leaving the dorsal column or brainstem, as well as any cranial nerves, abdominal, thoracic, or trigeminal ganglia nerves, nerve bundles of the cerebral cortex, deep brain and any sensory or motor nerves. 
         [0032]    The neural stimulation system can include an implantable lead that includes an enclosure that houses one or more conductive antennas (for example, dipole or patch antennas), internal circuitry for frequency waveform and electrical energy rectification, and one or more electrode pads allowing for neural stimulation of tissue. The neural stimulation system may receive microwave energy from an external source. The implantable lead may be 1.3 mm diameter or smaller. Particular implementations of the circuitry, antennas and pads are described in PCT Application PCT/US2012/023029, which is incorporated herein by reference. 
         [0033]    In various embodiments, the implantable lead is powered wirelessly (and therefore does not require a wired connection) and contains the circuitry necessary to receive the pulse instructions from a source external to the body. For example, various embodiments employ internal dipole (or other) antenna configuration(s) to receive RF power through electrical radiative coupling. This can allow such leads to produce electrical currents capable of stimulating nerve bundles without a physical connection to an implantable pulse generator (IPG) or use of an inductive coil. This can be advantageous relative to designs that employ inductive coils to receive RF power through inductive coupling and then transfer the received power to a large IPG device for recharging, particularly since the the large IPG device for recharging can be as large as 100 mm by 70 mm. 
         [0034]    Furthermore, the electrical radiative coupling mechanism (for example, a dipole antenna) can be utilized to improve the form factor of a wireless lead and allow for miniature diameters, as small as 30 microns. For example, some implementations of the wireless lead, such as those discussed in association with  FIGS. 7-15 , can have diameters of less than 1.3 mm, and as small as 500 microns while still providing the same functionality as wired spinal cord stimulation leads. 
         [0035]    Electrical radiative coupling also allows for the transmission and reception of energy at greater depths with less degradation in efficiency than inductive coil techniques. This can provide an advantage over devices that employ inductive coupling since the efficiency of such implants is highly dependent on the distance separating the external transmitter coil and the implanted receiver coil. 
         [0036]    Various embodiments can also include distinct advantages over wired leads in regards to ease of insertion, cross connections, elimination of extension wires, and no requirement for an implantable pulse generator in order to administer a chronic therapy. Various implementations also may have an associated lower overall cost compared to existing implantable neural modulation systems due to the elimination of the implantable pulse generator, and this may lead to wider adoption of neural modulation therapy for patients as well as reduction in overall cost to the healthcare system. 
         [0037]      FIG. 1  illustrates two wireless paddle leads  200  (described in more detail below) being implanted through an extended-width introducer  202  into the epidural space. A lead  200  may be advanced and guided into the epidural space utilizing the extension tubing  201  with a handle for manipulating the lead  200 . The introducer  202  has an entry point  100  above lumbar spinal column  103  (shown in  FIG. 2 ). Once the introducer  202  is removed, the wireless paddle lead  200  can be anchored in place subcutaneously at entry point  100 . Thereafter, extension tubing  201  may remain implanted and may run from the skin placement to the wireless paddle leads  200 . 
         [0038]    In some embodiments, the tubing  201  contains a lumen for a stylet (otherwise referred to as an “injector lead wire,” a “guide-wire,” a “navigation wire,” or “a steer wire”), which can be used for placing the lead  200 . The stylet may be made of metal and can provide steerability strength during implantation of the wireless paddle lead  200 . After the wireless paddle lead  200  has been successfully deployed, the metal stylet may be removed. As will be discussed in association with  FIG. 7C , this lumen, or other lumens in tubing  201 , can be used to also house electronic circuitry. 
         [0039]      FIG. 2  illustrates a wireless paddle lead  200  being placed through an introducer  202  typically in the lumbar region in between the L1 and L2 vertebrae. For example, the introducer  202  may be inserted through a small incision in the skin  105  and in between the vertebrae  103 . In certain other embodiments, multiple wireless paddle leads  200 , wireless cylindrical leads  400  (as will be discussed in association with  FIGS. 8-15 ) and wireless semi-cylindrical leads  300  (as will be discussed in association with  FIGS. 8-15 ) can be inserted through the same channel of introducer  202 . Wireless paddle leads  200 , cylindrical leads  400  or semi-cylindrical leads  300  for spinal cord stimulation applications can then be implanted and placed against the dura  104  of the spinal column  102 , as described in association with  FIG. 3  below. 
         [0040]    In certain embodiments, wireless paddle leads  200 , cylindrical leads  400  or semi-cylindrical leads  300  may be adapted to be located within the epidural space of the spinal column, near or on the dura of the spinal column, in tissue in close proximity to the spinal column, in tissue located near the dorsal horn, dorsal root ganglia, dorsal roots, dorsal column fibers and/or peripheral nerve bundles leaving the dorsal column of the spine. 
         [0041]    In certain embodiments, wireless paddle leads  200 , cylindrical leads  400  or semi-cylindrical leads  300  can be adapted to be placed and secured to stimulate nerves leaving the spinal column for the treatment of a variety of conditions, such as, for example, pain, angina, peripheral vascular disease, gastrointestinal disorders. In other embodiments, wireless paddle leads  200  can be adapted to treat other conditions via neural stimulation of nerve bundles emanating from the spine. “Spinal cord tissue” and “nerve bundles emanating from the spine” generally refer to, without limitation, the nerve bundles ranging from spinal column levels C1 to L5, dorsal horn, dorsal root ganglia, dorsal roots, dorsal column fibers and peripheral nerve bundles leaving the dorsal column. 
         [0042]      FIG. 3  illustrates a wireless paddle lead  200  in place against the dura  104  of the spinal cord after being implanted into the human body for spinal cord stimulation applications. The small incision at the skin  105  can be stitched with a suture or sterile strip after placement of the anchoring mechanism  106 . Wireless paddle leads shown here may have electrodes that confine the current path in a direction generally perpendicular to the dura, as will be discussed in association with  FIG. 11C . This directionality may be desirable to zero in on a target particular tissue and to reduce electrical charges for efficacious stimulation. 
         [0043]      FIG. 4A  illustrates an example of an introducer  214  that can fit in between two vertebrae without the need for a surgical laminotomy or removal of any bone tissue. The introducer  214  includes a handle  212  for use by the medical staff during the insertion procedure. The width of each handle can be between about 8 mm and about 15 mm. The length of each handle can be between about 10 mm and about 18 mm. The thickness of the handle may be between about 2.5 mm and about 6 mm. The introducer  214  has an inner channel  215  that can house, for example, two wireless paddle leads  200  placed one at a time, sequentially through the same introducer channel. As illustrated, the example wireless paddle lead  200  can have a flat tip. 
         [0044]      FIG. 4B  shows a cross-sectional view of the introducer illustrated in  FIG. 4A . This cross-sectional view may also be known as a profile view. 
         [0045]      FIG. 5A  illustrates another example introducer  214  that can fit through the vertebrae without the need for a surgical laminotomy or removal of any bone tissue. The introducer  214  includes a handle  212  for use by the medical staff during the insertion procedure. The introducer  214  has an inner channel  217  that can house, for example, two slim factor wireless paddle leads  220  placed one on top of the other. The two slim factor wireless paddle leads  220  can be stacked vertically in the inner channel  217  at the same time. As illustrated, the example wireless paddle lead  220  can have a pointed tip  219  that aids in directing the paddle lead through the tight epidural space of a smaller patient. The example wireless paddle lead  220  can also have a flat tip that aids in laying the electrode columns parallel with the spine from a fluoroscopic view or rounded tip that aids in both laying the electrode columns parallel with the spine and in directing the paddle lead through the epidural space. 
         [0046]      FIG. 5B  shows a cross-sectional view of the introducer illustrated in  FIG. 5A . This cross-sectional view may also be known as a profile view. 
         [0047]      FIG. 6A  illustrates the distal tip of a wireless paddle lead  200 . The wireless paddle lead  200  may include, for example, four electrodes  203  and the spacers between the electrodes. The wireless paddle lead  200  can include between two to sixteen electrodes  203  located on the distal end of the lead (not shown). The distal tip may have a height of between about 1.3 mm and about 2.0 mm, and a width between about 2.0 mm and about 4.0 mm. The electrodes  203  may have a longitudinal length between about 1.0 mm and about 6.0 mm from the distal tip toward the proximal tip and a width of between about 0.4 mm and about 3.0 mm. The total electrode surface area of the lead  200  may be between about 0.8 mm 2  and about 60.0 mm 2 . The spacing between the electrodes  203  may be between about 1 mm and about 6 mm from distal to proximal. 
         [0048]    The various leads described herein may include anywhere from one to sixteen electrodes, any of which can be designated by the programmer as either a cathode or an anode. For example, electrodes  203  can include multiple cathodes coupled to the targeted tissue as well as at least one anode. The electrode array can receive electrical stimulation waveform pulses ranging from 0 to 10V peak amplitude at a pulse width reaching up to a maximum of 1 millisecond. The polarity of the electrodes can produce various volume conduction distributions from the cathodes to the anodes to inhibit or excite surrounding nerve tissue, which may include A-δ and/or primary or secondary c-fiber afferents. To minimize electrode impedance, the electrodes may be made of a conductive, corrosion resistant, biocompatible material such as, for example, platinum, platinum-iridium, gallium-nitride, titanium-nitride, or iridium-oxide. 
         [0049]    Excluding the electrodes  203 , which are coupled to the surrounding tissue, the remaining portions of the wireless lead embodiments described herein may be insulated from surrounding body tissue partially or totally by an external coating layer of biocompatible dielectric material with a low dielectric constant. Materials with rigidity similar to that of tissue can be used to reduce the risk of migration and the development of fibrous scar tissue. Such fibrous scar tissue can increase electrode-tissue impedance. If the electrode-tissue impedance can be kept low, less energy may be consumed to achieve stimulation of the targeted tissues. 
         [0050]    In certain embodiments, the wireless paddle lead  200  can have a rounded tip  211  at the distal end. Rounded tip  211  can be a non-conductive tip. Rounded tip  211  can have a length of between 0.5 mm and 2.0 mm, and a smooth finish for navigating the lead through the epidural space. 
         [0051]    In certain embodiments, the wireless paddle lead  200  can have a pointed tip  219  at the distal end. Pointed tip  219  can be a non-conductive tip. Pointed tip  219  can have a length of between about 2.0 mm and about 6.0 mm. Pointed tip  219  can enhance the steering capability when the wireless paddle  200  is being deployed. 
         [0052]      FIG. 6B  shows the cross-sectional views of the distal end of three embodiments of a wireless paddle lead. For example, in certain embodiments, the wireless paddle lead  200  may be a slim factor wireless paddle lead  220 . As illustrated in  FIG. 6B , the slim factor wireless paddle lead  220  can be thinner than a regular wireless paddle lead  221 . For example, slim-factor wireless paddle lead may be between about 1.0 mm and about 1.3 mm in height, which can allow multiple slim-factor wireless paddle leads to be implanted simultaneously or sequentially through an introducer  214 . For example, in certain embodiments, wireless paddle leads  200  may be a slim-factor concave wireless paddle lead  207  having a concave profile of between about 1.0 mm and 1.5 mm, concave edges of about 0.2 mm by about 0.3 mm. The concave profile may refer to the height of the slim-factor concave wireless paddle lead  207 . The concave edge may refer to the dimension of the concave shape corner the slim-factor concave wireless paddle lead  207 . The slim factor concave wireless paddle lead  207  may be placed as close as possible to the dorsal spinal column. 
         [0053]    In certain embodiments, at least one additional wireless lead may be placed in parallel or offset with the initial wireless lead. In some embodiments, the wireless leads may be activated sequentially. In other embodiments, wireless leads can be activated simultaneously. 
         [0054]      FIGS. 7A and 7B  respectively illustrate the dorsal and ventral sides of an implementation of a wireless paddle lead  200 . For example, electrodes  203  and between two to eight antenna coupling contacts  222  may be placed on different sides of the wireless paddle lead  200 . As discussed in association with  FIG. 6A , two to sixteen electrodes  203  can be located on the distal end and embedded into the electrically insulative material  205  of the wireless lead  200 . 
         [0055]    For example, antenna  208  may be coupled to tissue through the antenna coupling contacts  222  located on the ventral side of the wireless paddle lead  200 . The antenna can be, for example, a dipole antenna. Some embodiments may have only one dipole antenna, other embodiments may have multiple antennas of any given length. For example, without limitation, some embodiments may have between two and ten dipole antennas, while other embodiments can have more than ten dipole antennas or more than twenty dipole antennas. In some embodiments, a dipole antenna can range from about 100 microns to about 10 cm in length. In other embodiments, an antenna can consist of any linear dipole configuration ranging from about 20 microns to about 3 mm in thickness. The antenna  208  may also be a folded dipole antenna instead of straight dipole antenna. 
         [0056]    Antenna  208  may be configured to receive RF energy from exterior antennas. RF wave propagation energy is divided into two regions, the radiative region and the reactive region. The radiative region is within 2D 2 /λ and the radiated power varies with distance from the antenna. For a short dipole antenna, the reactive component is approximately λ/2π. The induced field for antennas placed in biological tissue is a function of body geometry, tissue properties, and the exposure conditions. The efficiency of the RF waveform inside a lossy media, such as body tissue, is attenuated by the tissue as it propagates. To increase the power efficiency of a small antenna in lossy matter, the dipole antenna configuration can be optimized at high frequencies to minimize losses, such as, for example, from about 800 MHz to 5.8 GHz or greater. 
         [0057]    The antenna coupling contacts  222  in certain embodiments may have a longitudinal length between about 1.0 mm and about 6.0 mm from the distal tip toward the proximal tip and a width of between about 1.0 mm to about 2.5 mm. The spacing between the antenna coupling contacts  222  may be between about 30 mm and about 80 mm. The antenna coupling contracts  222  may improve the efficiency of the radiative coupling between internal antenna  208  and the antenna(s) (not depicted) located externally to the body. The antenna coupling contracts  222  may be made of noncorrosive metals, such as, for example, platinum, platinum-iridium, gallium-nitride, titanium-nitride, or iridium-oxide. 
         [0058]    Antenna coupling contacts  222  may be connected by conducting wires  210  to the antenna(s)  208  and the waveform conditioning circuit  209 . Waveform conditioning circuitry  209  may include, for example electronic components such as, for example diodes, resistors and capacitors. Waveform conditioning circuitry  209  can use the incoming energy to provide a stimulation waveform to the electrodes for excitation of nerve tissue. In some embodiments, frequencies from about 800 MHz to about 5.8 GHz may be received by the implanted antenna  208 . The stimulating waveform released into the tissue from electrodes  203  is rectified to provide waveforms at lower frequencies, e.g., at typically from about 5 Hz to about 1000 Hz. 
         [0059]    Waveform conditioning circuitry  209  is configured to rectify the waveform signal received by implanted antenna  208 . Waveform conditioning circuitry  209  may also have charge balance microelectronics to prevent the corrosion of the electrodes. To minimize reflection of the energy back from the electrodes into the circuitry, waveform-conditioning circuitry  209  may include isolation circuits to block high frequency signals. 
         [0060]      FIG. 7C  illustrates the ventral side of another embodiment of a wireless paddle lead  200 , in which the implanted antenna  208  is separated from the distal end  205  of wireless paddle lead  200 . In some embodiments, the implanted antenna  208  may be placed remotely from the distal end  205  of the wireless paddle lead  200  and inside a lumen in extension tubing  201  within the lead body. In some embodiments, the implanted antenna  208  may be the extension line of one of the antenna coupling contacts  304 . In some embodiments, antenna coupling contacts  304  may be located proximal to the electrodes  203 . Antennas  208  may be further connected to the waveform conditioning circuitry  209  via shielded wiring  210 . The waveform conditioning circuitry  209  may be directly wired to the electrodes  203  (located on the ventral side). 
         [0061]    In some embodiments, the wireless leads described herein may have multiple layers. These layers can include, without limitation, encasing material close to the electrodes with a biocompatible compound that elicits minimal scar tissue formation. In addition, layers may include polymers such as, without limitation, polymethymethacrylate (PMMA), polydimethylsiloxane (PDMS), parylene, polyurethane, polytetrafluoroethylene (PTFE), or polycarbonate. Another layer of a material that may be included contains a small relative permeability and low conductivity located above the antennas  208  to allow for optimal coupling with an exterior antenna (not depicted). Yet another layer can comprise a coating of a silicone elastomer to assist in preventing migration of the wireless lead to the surrounding tissue. 
         [0062]      FIGS. 8 and 9  illustrates an example of a wireless cylindrical lead  400  or a wireless semi-cylindrical lead  300  being implanted in the epidural space using needles  301 . Cylindrical wireless leads may also be referred to as circumferential leads, while semi-cylindrical wireless leads may also be referred to as semi-circumferential or semi-elliptical wireless leads. Wireless cylindrical leads  400  or wireless semi-cylindrical leads  300  can be introduced into the body through needle  301 . The needle  301  may be a tuohy needle, 14-Gauge, or smaller (for example, 22 Gauge). Alternatively, the wireless leads  300  and  400  may be introduced into the epidural space through an introducer  202  (see, for example,  FIG. 1 ). Introducers  202  or needle  301  may be inserted through the outer skin of the body through a small incision in the skin  105  and in between the vertebrae  103  at no more than a 45-degree angle, lateral to the spinous processes off the midline, and placed against the dura  104  of the spinal column  102  to lie perpendicularly to the spinal cord. The wireless leads  300  or  400  can contain extension tubings  201  that terminate just under the entry point  100  of the skin. The wireless lead may be guided upwards in the epidural space according to the angle of introducer or needle insertion. After the wireless lead has been placed, a subcutaneous anchor is used to stop vertical and horizontal migration of the wireless lead. 
         [0063]      FIG. 10  illustrates embodiments of a cylindrical wireless lead  300  or semi-cylindrical wireless lead  400  after being implanted. A cylindrical  300  or semi-cylindrical  400  wireless lead may be placed against the dura  104  of the spinal cord and the small incision at the skin  105  is stitched with a suture or sterile strip after placement of the anchoring mechanism  106 . 
         [0064]      FIG. 11A-11C  respectively illustrate the cross-sectional views of the placement of a wireless semi-cylindrical lead  300 , a wireless cylindrical lead  400 , and a wireless paddle lead  200  after successful implantation in relation to the dura  104  of the spinal cord  101 . 
         [0065]      FIG. 11  A shows the placement of a wireless semi-cylindrical lead  300  relative to the dura  104  of the spinal cord  101 . The wireless semi-cylindrical (also referred to as half-circumferential or half-elliptical) lead  300  may have electrodes that are straight, as depicted in  FIG. 12A , or that are concave and half-cylindrical in shape. Semi-cylindrical electrodes can match the shape of the enclosure. The semi-cylindrical shape of the enclosure of lead  300  may help the lead to mechanically conform to the contour of the spinal column  102 . The shape of the enclosure can also assist in targeting the electrical volume conduction inward towards the dura  104 , and avoid radiating energy outwards towards the ligaments, vertebrae and skin (non-excitable tissue). More generally, the conducting field generated by the electrodes is uni-directional in nature because the conducting field culminates mainly in the enclosure and electrode faces are pointed in one direction. By removing the unnecessary emission from over 270 degrees of a cylindrical electrode (see, for example, in  FIGS. 14B and 15 ) radiating towards non-excitable tissue, the semi-cylindrical wireless lead  300  can reduce the amount of energy required for a successful stimulation. Therefore, the benefits of the example semi-cylindrical wireless lead  300  may include the directional delivery of stimulation energy as confined by the shape of the electrode. 
         [0066]      FIG. 11B  shows the placement of a wireless cylindrical lead  400  relative to the dura  104  of the spinal cord  101  after successful implantation. As depicted, the wireless cylindrical lead  400  is placed against dura  104 . 
         [0067]      FIG. 11C  shows the placement of a wireless paddle lead  200  relative to the dura  104  of the spinal cord  101  after successful implantation. As depicted, the wireless paddle lead  200  is placed against dura  104 . Wireless paddle lead  200  may have electrodes that confine the current path in a direction generally perpendicular to the dura. This directionality may be desirable to zero in on a target particular tissue and to reduce electrical charges for efficacious stimulation 
         [0068]      FIGS. 12A and 12B  illustrate perspective and profile views, respectively, of an implementation of a wireless semi-cylindrical lead  300 . The semi-cylindrical lead  300  can have, in certain embodiments between two to sixteen electrodes  203  at the distal end  205 , each with a diameter typically between about 0.8 mm and about 1.4 mm, and concave ventral aspects with bend radiuses typically between about 0.6 mm and about 3.0 mm. The electrodes  203  may have longitudinal lengths between about 1.0 mm and about 6.0 mm from the distal tip towards the proximal tip with widths typically between about 0.4 mm and about 1.0 mm. The total electrode surface area of the wireless lead  300  is typically between about 0.8 mm 2  and about 60.0 mm 2 . The spacing between the electrode contacts is typically between about 1.0 mm and about 6.0 mm. The distal tip of the lead body may be a non-conductive tip that is pointed with a length of between about 0.5 mm and about 2.0 mm, and a smooth finish for navigating the lead through the epidural space. 
         [0069]    The wireless semi-cylindrical lead  300  may include between two to eight antenna coupling contacts  304 , as illustrated in association with  FIG. 7C , that are wired to the implanted antenna(s)  208  and the flexible circuits  206  (as illustrated in association with  FIGS. 12 and 13 ). The antenna coupling contacts  304  may be proximal of the electrodes  203 . The antenna coupling pads  304  may have a longitudinal length of between about 1 mm and about 6 mm from the distal tip to the proximal tip. The spacing between the antenna coupling contacts  304  is typically between 30 mm and 80 mm. In some embodiments, small antenna coupling contacts  303 , to be discussed in association with  FIG. 13C , may be used. Antenna coupling contacts  303  may have a diameter between about 0.2 mm and about 0.6 mm. 
         [0070]    Embodiments of wireless leads described herein can have a larger surface area directed towards the dura mater than existing percutaneous leads. This increased surface area can lower the tissue to electrode impedance values and can lead to larger currents for stimulation. 
         [0071]      FIGS. 13A-13C  variously illustrate electronic components included in two different embodiments of the wireless lead, namely, a wireless semi-cylindrical lead  300  and a wireless cylindrical lead  400 . 
         [0072]      FIG. 13A  shows an example wireless lead (e.g. a wireless semi-cylindrical lead  300  or a wireless cylindrical lead  400 ) with extension tubing  201 . The tubing  201  may house electrodes  203 , implanted antenna  208 , waveform conditioning circuitry  209 , and wires  210 . As discussed above in association with  FIGS. 7A-7B , the waveform conditioning circuitry  209  can include components for rectifying the received RF energy and for charge balancing the waveform for tissue stimulation. 
         [0073]    One or more flexible circuits  206  may be used to carry various parts of the electronic components. For instance, the flexible circuits  206  may include the waveform conditioning circuitry  209  and implantable antenna(s)  208 . The flex circuit may also include portions of the wires  210 , which connect the electronics, such as circuitry  209 , to the electrodes  203 . The flexible circuits  206  may be between about 15 mm and about 90 mm long, and about 0.7 mm and about 2.0 mm wide. The total height of the flexible circuit  206  with the waveform conditioning circuitry  209  may be between about 0.2 mm and about 0.4 mm. The flexible circuit  206 , when placed inside of the cylindrical wireless lead  400  may undergo a bend radius under about 0.5 mm. As illustrated in  FIG. 13A , in some embodiments, the flexible circuit  206  may contain a conductive trace to act as an antenna  208 . 
         [0074]      FIG. 13B  shows another example of a wireless lead (e.g. a wireless semi-cylindrical lead  300  and a wireless cylindrical lead  400 ) encapsulated that includes tubing  201 . The tubing houses antenna(s)  208  and the waveform conditioning circuitry  209 , both of which may be formed on a flex circuit  206  similar to the flex circuit described with respect to  FIG. 13A . At least a portion of the wires  210  may be formed on the flex circuit as well. Wires  210  connect, for example, the circuitry  209  to the electrodes (not shown in  FIG. 13B ). Wires  210  also connect the antenna  208  to tissue exposed ring antenna coupling contacts  304 . Tissue exposed ring antenna coupling contacts  304  can be circumferential rings with outer diameter between about 0.8 mm and about 1.4 mm, and longitudinal lengths between about 0.5 mm and about 6.0 mm. 
         [0075]      FIG. 13C  shows yet another example wireless lead (e.g. a wireless semi-cylindrical lead  300  and a wireless cylindrical lead  400 ) with extension tubing  201 . The extension tubing  201  houses antenna(s)  208  and the waveform conditioning circuitry  209 , both of which may be formed on a flex circuit  206  similar to the flex circuit described with respect to  FIG. 13A . At least a portion of the wires  210  may be formed on the flex circuit as well. Wires  210  connect, for example, the circuitry  209  to the electrodes (not shown in  FIG. 13C ). Wires  210  also connect the antenna  208  to tissue exposed small antenna coupling contacts  303 . Tissue exposed small antenna coupling contacts  303  may be made of a conductive cylindrical piece of metal of diameter between about 0.2 mm and about 0.6 mm and thickness of between about 0.2 mm and about 0.6 mm. Tissue exposed small antenna coupling contacts  303  may contact tissue and can be embedded into the electrically insulative material  205 . 
         [0076]      FIG. 14A  illustrates a cross-sectional view of an embodiment of a fully cylindrical wireless lead  400  or a semi-cylindrical wireless lead  300  at a position proximal to the distal tip. The embodiment shown is a multi-lumen extrusion  305  having a center lumen  204  and multiple orbital lumens  306  (for example, one to ten or more). The multi-lumen extrusion  305  may be proximal to the single-lumen extrusion  307 , shown in the right graph, on one wireless lead (for example, a fully cylindrical wireless lead  400  or a semi-cylindrical wireless lead  300 ). The multi-lumen extrusion  305  may act as backbone for guiding the conducting wires  210 , housed in side lumens  306 , and a stylet (as discussed in association with  FIG. 1 ) placed through the center lumen  204 . The multi-lumen plastic extrusion  305  can be made up of between one to ten or more orbital lumens  306 , each with inner diameters of between about 0.1 mm and about 0.6 mm. The multi-lumen plastic extrusion  305  may have an outer diameter of between about 0.8 mm and about 1.4 mm. In certain embodiments, the multi-lumen extrusion  305  may be ablated (i.e., heated to be deformed) to a final outer diameter of between about 0.6 mm and about 0.9 mm which allows the extrusion  305  to connect male to female into a single lumen extrusion  307 , as shown in the right graph. A navigation stylet may be placed inside the inner lumen  204  to guide the wireless lead into the epidural space. The inner lumen  204  maintains a clear channel without obstruction and may be fused with the single lumen extrusion  307  at the interconnection between extrusions  305  and  307  and after the above-mentioned ablation. 
         [0077]      FIG. 14B  illustrates a cross-sectional view of another embodiment of a fully cylindrical wireless lead  400  or a semi-cylindrical wireless lead  300  at a position proximal to the distal tip. This embodiment is a single-lumen extrusion  307 , which may have inner diameter of between about 0.3 mm and about 1.4 mm. The single lumen extrusion  307  may be pulled around the outside of, for example, the wireless semi-cylindrical lead  300  and heat formed to match an outer diameter of between about 0.8 mm and about 1.4 mm. The single lumen extrusion  307  can leave sufficient empty space for the flexible circuit  206  to be encapsulated inside. The inner lumen  204  may be offset by a distance indicated by  308  inside the single lumen  307  to provide a gap space for the flexible circuit  206 . Conducting wires  210  from the side lumens  306  may connect to terminal features (not depicted) on the flexible circuit  206 . The gap space inside the single-lumen extrusion  307  between the flexible circuit  206  and inner lumen  204  may be back-filled with a biocompatible polymer to give added rigidity for protecting the flexible circuit components  206  and conducting wires  210 . 
         [0078]      FIG. 14C  illustrates a cross-sectional view towards the distal end of a semi-cylindrical wireless lead  300 . For a semi-cylindrical wireless lead  300 , the concave multi-lumen extrusion  309  may house the conducting wires  210  running from the flex circuit  206  to the electrodes  203 . The concave shape of multi-lumen extrusion  309  may allow semi-cylindrical wireless lead  300  to conform to the curvature of the spinal cord. The bend radius of the concave dorsal aspect is between about 0.6 mm and about 3.0 mm. The concave multi-lumen extrusion  309  may contain between one and ten or more orbital lumens  306  acting as channels for conducting wires and a central lumen  204  for the stylet. The lumens  204  and  306  may have inner diameters of between 0.1 mm and 0.6 mm. The orbital lumens  306  may be drilled into from the dorsal side during manufacturing to create channels to connect the conducting wires  210  to the electrodes  203 . 
         [0079]      FIG. 15  illustrates an example of a fully circumferential wireless lead. The cylindrical wireless lead  400  may have between two and sixteen cylindrical electrodes  203  on its distal end with a diameter between about 0.8 mm and about 1.4 mm for epidural spinal cord stimulation applications. The electrodes  203  may have a longitudinal length of between about 1.0 mm and about 6.0 mm from the distal tip toward the proximal tip. The spacing between the electrode contacts may be between about 1.0 mm and about 6.0 mm. The total electrode surface area of the cylindrical wireless lead body  400  may be between about 1.6 mm 2  and about 60.0 mm 2 . The distal tip of the cylindrical wireless lead body  400  may be a non-conductive tip that is rounded with a length of between about 0.5 mm and about 1.0 mm, with a smooth finish for navigating the lead through the epidural space. Between two to eight tissue exposed ring antenna coupling contacts  304  may be proximal to the electrodes  203 . The tissue exposed circular antenna coupling contacts  304  may have a longitudinal length of between about 1.0 mm and about 6.0 mm from the distal tip toward the proximal tip. The spacing between the tissue-exposed circular antenna coupling contacts  304  may be between about 30 mm and about 80 mm. In certain embodiments, tissue exposed small antenna coupling contacts  303  with a diameter between about 0.2 mm and about 0.6 mm may be used in lieu of the illustrated tissue exposed small antenna coupling contacts  303 . Extension tubing  201 , as discussed in association with  FIGS. 1 ,  7 C,  8  and  9 , can provide an enclosure that houses, for example, flex circuitry  206 . Flex circuitry  206  has been discussed in association with  FIGS. 13A to 13C . Extension tubing  201  may include a center lumen  204 . As discussed in association with  FIG. 14A , a stylet can be placed through center lumen  204  to provide guidance during implantation of lead  400  into, for example, through a lumen in to a human body. 
         [0080]    Various implementations of the technology may allow placement of wireless lead in the epidural space, between the dura mater and arachnoid membranes, or subdurally in the intrathecal space, where significant reactions and scarring would be minimized. Insertion in any of these locations may be done by injecting the device from a smaller gauge needle (e.g., 14 to 22-gauge needle or out of a cannula steered to the proper position by a removable stylet). In some implementations, once in position, no further skin incisions or placement of extensions, receivers or implanted pulse generators are needed. Various implementations of the wireless neural modulation system may have significant advantages due to the small size and lack of extension wires for transfer of energy, allowing placement with minimal trauma and long term effective therapy in places where larger implantable devices could cause more scar tissue and tissue reactions that may affect efficacy and safety. 
         [0081]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.