Patent Description:
Implantable electrical stimulation systems may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions such as headaches, lower back pain and incontinence.

In many electrical stimulation applications, it is desirable for a stimulation system, typically comprising a therapeutic lead (a lead comprises electrodes and electrical connections), to provide electrical stimulation to one or more precise locations within a body. Typically, stimulation is provided using one or more stimulation electrodes that are configured to transfer electrical pulses to tissue with respect to one or more electrical returns.

US application <CIT> describes a neurostimulation paddle lead carrying a plurality of electrodes comprising at least four columns of electrodes having a spacing between two inner electrode columns less than a spacing between the inner electrode columns and adjacent outer electrode columns. The inner electrode columns may also be longitudinally offset from the outer electrode columns. The methods and neurostimulation systems steer current between the electrodes to modify a medial-lateral electrical field created adjacent spinal cord tissue.

US application <CIT> describes an implantable electrode array, including an organic substrate material configured to be implanted into an in vivo environment and to optionally dissolve after implantation and be absorbed, and an electrode mounted to the organic substrate material and configured to acquire signals generated by the in vivo environment. The electrode array includes a connection pad mounted to the organic substrate, and an MRI-compatible conductive trace formed between the electrode and the connection pad.

<CIT> also describes a system for a neurostimulator coupled to electrodes.

Anatomy and treatment protocols can vary greatly - it is therefore advantageous to provide a stimulation system that can be configured to a high degree. Systems and devices are known which comprise a plurality of electrodes proximate to each other in the lead, allowing one or more electrodes to be selected for use. Some electrodes may be selectable as either stimulation or return electrodes, allowing some tuning of the region of stimulation. The degree of electrical energy, such as voltage, current and/or power may also be varied, to provide some degree of control over the level of stimulation.

It is an object of the invention to provide an improved tissue stimulation system that provides additional configuration possibilities and adjustments.

According to a first aspect of the present disclosure, there is provided a tissue stimulation system comprising an implantable end and a stimulation energy source, the implantable end comprising: an elongated substrate, disposed along a longitudinal axis, the substrate having a first and second surface disposed along substantially parallel transverse planes; one or more stimulation electrodes, comprised in the second surface and configured to transmit energy, in use, to human or animal tissue; and one or more proximal return electrodes, comprised in the first surface or second surface, disposed proximate the one or more stimulation electrodes; the stimulation energy source further comprising: one or more distal return electrodes, disposed distantly from the one or more stimulation electrodes; and a pulse energy controller; the tissue stimulation system further comprising: one or more interconnections between the implantable end and a stimulation energy source, configured and arranged to connect the output of the pulse generator to the one or more stimulation electrodes whereby electrical energy may be transferred, during use, as one or more electrical stimulation pulses to the one or more stimulation electrodes with respect to an electrical return; wherein: the one or more proximal return electrodes are configured as a first part of the electrical return for the one or more stimulation electrodes; and the one or more distal return electrodes are configured as a second part of the electrical return for the one or more stimulation electrodes; the pulse energy controller further comprising a ratio controller, configured and arranged to modify the electrical potential and/or current ratio of the first part to the second part.

By providing an implantable end with one or more proximal return electrodes proximate the one or more stimulation electrodes, a substantially transverse electric field may be provided. It may then provide a more concentrated current density and distribution in directions approximately perpendicular to the longitudinal axis (transversely-oriented electric field). This provides an additional degree of configuration for tissue stimulation systems and devices.

In addition, a potential and/or current ratio controller provides a convenient way to concentrate or diffuse this substantially transverse field in combination with one or more distal return electrodes comprised in the stimulation energy source: when the electrical return is mainly provided by the one or more proximal return electrodes in the implantable end, the electric field is stronger (more local). Alternatively, when the electrical return is mainly provided by the one or more distal return electrodes in the stimulation energy source, the electric field is weaker (more global).

It may be advantageous to configure and arrange the one or more distal return electrodes to be disposed more than <NUM>, preferably more than <NUM>, from the one or more corresponding stimulation electrodes. Additionally or alternatively, it may be advantageous to configure and arrange the one or more proximal return electrodes (<NUM>) to be disposed within less than <NUM>, preferably less than <NUM>, from the one or more corresponding stimulation electrodes.

In this context, corresponding means the one or more stimulation electrodes that are configured, in use, to transmit energy to tissue with respect to at least one distal and at least one proximal return electrodes.

According to a further aspect of the present disclosure, there is provided a tissue stimulation system wherein the one or more proximal return electrodes are elongated along the longitudinal axis.

Having elongated electrodes provides stimulation over extended longitudinal dispositions.

According to another aspect of the present disclosure, there is provided a tissue stimulation system wherein the one or more stimulation electrodes have a first extent along the longitudinal axis, and the one or more proximal return electrodes have a second extent along the longitudinal axis, the second extent being substantially the same or greater than the first extent.

The control over the electric field is preferably provided over at least substantially the same length (extent along the longitudinal axis) as the one or more stimulation electrodes. If the proximal return electrodes are substantially longer (greater extent), they may be operated as a proximal return electrode for more than one stimulation electrodes - so if another stimulation electrode is selected, a further reconfiguration of the electrodes may be avoided. In other words, if a different active stimulation electrode is selected, this typically results in stimulation energy being applied at a different longitudinal disposition. A substantially longer proximal return electrode may provide an electrical return for the currently selected stimulation electrode and the previously selected stimulation electrode.

According to a further aspect of the present disclosure, there is provided a tissue stimulation system wherein the one or more stimulation electrodes are elongated along the longitudinal axis.

By being elongated, stimulation energy may be applied over a plurality of dispositions along the longitudinal axis. This greatly reduces the chance that, after implantation, the electrode is not proximate enough to a stimulation target. Particularly, when the target is a nerve.

According to yet another aspect of the present disclosure, there is provided a tissue stimulation system wherein the one or more proximal return electrode comprises two proximal return electrode regions, electrically connected to each other, the two proximal return electrode regions being disposed on opposing sides of the one or more stimulation electrode.

By providing suitably configured return electrodes with two regions, treatment current density and the position where the highest current densities occur, may be predetermined and/or controlled. In some cases, a very high degree of control may not be possible due to, for example, the nature of the treatment, the system and/or device, the implant site and the individual patient - in such cases, the configuration of the return electrodes may exert a degree of influence on the current density and its distribution.

According to a further aspect of the present disclosure, there is provided a tissue stimulation system wherein the two proximal return electrode regions are two non-contiguous electrode regions, electrically connected to each other; and each return electrode region is separated at least partially along the first transverse axis from the one or more stimulation electrodes by an electrical insulator.

As surface area and relative disposition are among the factors that influence treatment current density and distribution, providing at least two non-contiguous regions may provide a high degree of control. In addition, the shape and proximity to the corresponding stimulation electrode may also provide a degree of control.

According to a further aspect of the present disclosure, there is provided a tissue stimulation system wherein the two proximal return electrode regions are comprised in a substantially contiguous proximal return electrode.

In general, it is advantageous to maximize the tissue contact-area of the one or more return electrodes as this increase the efficiency of energy transfer to the tissue through the one or more stimulation electrodes. In addition, when using a substrate, such as LCP (Liquid Crystal Polymer), which may be easily manipulated using semiconductor processes known to the skilled person, such as deposition, etching and lithography - this means that a high degree of control may be exerted on the shape, dimensions (extent), disposition and electrical, physical & mechanical properties of the return electrode.

According to a still further aspect of the present disclosure, there is provided a tissue stimulation system wherein one or more of the two proximal return electrode regions extend along the first transverse axis (<NUM>) between an edge of the one or more corresponding stimulation electrodes and an edge of the substrate.

In general, it is advantageous to maximize the tissue contact-area of the one or more return electrodes as this increase the efficiency of energy transfer to the tissue through the one or more stimulation electrodes.

According to a still further aspect of the present disclosure, a tissue stimulation system is provided wherein a further proximal return electrode is comprised in the second surface.

The second surface also comprises the one or more stimulation electrodes, so the space available for one or more return electrodes may be limited. There are fewer restrictions regarding the space available on the first surface for the one or more return electrodes. Having one or more proximal return electrode on both surfaces provides a high degree of flexibility for configuration.

According to another aspect of the present disclosure, a tissue stimulation system is provided wherein a plurality of stimulation electrodes is provided, each having one or more corresponding proximal return electrodes.

This allows stimulation to be provided at different positions along the longitudinal axis by predetermining and/or controlling the energy passing through one or more of the electrodes.

According to another further aspect of the present disclosure, there is provided a tissue stimulation system wherein the combined tissue contact-area of the one or more proximal return electrodes and the one or more distal return electrodes is no less than the tissue contact-area of the one or more stimulation electrodes.

Features and advantages of some embodiments of the present invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, and which are not necessarily drawn to scale, wherein:.

In the following detailed description, numerous non-limiting specific details are given to assist in understanding this disclosure.

In general, stimulation systems described herein may comprise a stimulation energy source and an implantable end - the implantable end comprises one or more stimulation electrodes. "Implantable end" means that at least this section of the stimulation system is configured and arranged to be implanted. Optionally, one or more of the remaining sections of the stimulation systems may also be configured and arranged to be implanted.

<FIG> depict longitudinal cross-sections through a first embodiment <NUM> of an implantable end (lead) of a stimulation system <NUM>, <NUM> comprising:.

To clarify the different views, the axes are given nominal directions:.

For example, the elongated substrate <NUM> may comprise an elastomeric implantable end composed of silicone rubber, or another biocompatible, durable polymer such as siloxane polymers, polydimethylsiloxanes, polyurethane, polyether urethane, polyetherurethane urea, polyesterurethane, polyamide, polycarbonate, polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polysulfone, cellulose acetate, polymethylmethacrylate, polyethylene, and polyvinyl acetate. Suitable examples of polymers, including LCP (Liquid Crystal Polymer), are described in "<NPL>), In particular, Table <NUM> is included here as reference, depicting the properties of Polyimide (UBE U-Varnish-S), Parylene C (PCS Parylene C), PDMS (NuSil MED-<NUM>), SU-<NUM> (MicroChem SU-<NUM><NUM> & <NUM> Series), and LCP (Vectra MT1300).

Flexible substrates <NUM> are also preferred as they follow the contours of the underlying anatomical features very closely. Very thin substrates <NUM> have the additional advantage that they have increased flexibility.

Preferably, the flexible substrate <NUM> comprises an LCP, Parylene and/or a Polyimide. LCP's are chemically and biologically stable thermoplastic polymers which allow for hermetic sensor modules having a small size and low moisture penetration.

Advantageously, an LCP may be thermoformed allowing complex shapes to be provided. Very thin and very flat sections of an LCP may be provided. For fine tuning of shapes, a suitable laser may also be used for cutting. For example, LCP substrates <NUM> with thicknesses (extent along the second transverse axis <NUM>) in the range <NUM> microns (um) to <NUM> microns (um) may be used, preferably <NUM> microns (um) to <NUM> microns (um). For example, values of <NUM> (micron), <NUM>, <NUM>, or <NUM> may be provided. Similarly, substrate widths (extent along the first transverse axis <NUM>) of <NUM> to <NUM> may be provided using LCP, for example.

At room temperature, thin LCP films have mechanical properties similar to steel. This is important as implantable substrates <NUM> must be strong enough to be implanted, strong enough to be removed (explanted) and strong enough to follow any movement of the anatomical feature and/or structure against which it is implanted.

LCP belongs to the polymer materials with the lowest permeability for gases and water. LCP's can be bonded to themselves, allowing multilayer constructions with a homogenous structure.

In contrast to LCP's, polyimides are thermoset polymers, which require adhesives for the construction of multilayer substrates. Polyimides are thermoset polymer material with high temperature and flexural endurance.

An LCP may be used, for example, to provide a substrate having multilayers (not depicted) - in other words, several layers of <NUM> (micron) thickness. Electrical interconnections and/or interconnect layers may also be provided by metallization using techniques from the PCB (Printed Circuit Board) industry, such as metallization with a bio-compatible metal such as gold, silver or platinum. Electro-plating may be used. These electrical interconnections and/or interconnect layers may be used to provide electrical energy to any electrodes.

The implantable end of the system <NUM> depicted in <FIG> further comprises:.

"Comprised in the second surface" means that stimulation electrode <NUM> is relatively thin, and attached to the second surface <NUM>. The electrode <NUM> may also be embedded in the second surface <NUM>.

In general, one or more stimulation electrodes <NUM> may be provided. The number, dimensions and/or spacings of the stimulating electrodes <NUM> provided in the implantable end <NUM> may be selected and optimized depending on the treatment - for example, if more than one electrode <NUM> is provided, each electrode <NUM> may provide a separate stimulation effect, a similar stimulation effect or a selection may be made of one or two electrodes <NUM> proximate the tissues where the effect is to be created. The electrodes <NUM> may comprise a conductive material such as gold, silver or platinum, iridium, and/or platinum/iridium alloys and/or oxides.

<FIG> depicts two stimulation electrodes <NUM>, each elongated along the longitudinal axis <NUM>. Although an oval cross-section is suggested in <FIG>, any shape may be used, such a square, rectangular, triangular, polygonal, circular, elliptical, oval, and round. An elongated electrode (or strip electrode) as depicted in <FIG> may also be used.

The implantable end <NUM> of the system <NUM>, <NUM> depicted in <FIG> further comprises:.

The one or more interconnections <NUM> may be disposed between the first <NUM> and second surface <NUM>, comprised in the first surface <NUM>, comprised in the second surface <NUM>, or any combination thereof. In this case, they are depicted as being disposed between the first <NUM> and second surface <NUM>.

They may comprise one or more conductors, such as a metal, formed as required - for example, in one or more conductive: wire, strand, foil, lamina, plate, and/or sheet. They may be a substantially contiguous (one conductor) or comprise a plurality of conductors. In this, they are depicted as three wire-like conductors, encapsulated in the substrate <NUM>, disposed along the longitudinal axis <NUM>, two of which are connected to the two stimulation electrodes <NUM>. The third wire-like conductor is connected to the one proximal return electrode <NUM> (described below in more detail) via a further wire-like conductor, disposed along the second transverse axis <NUM>.

An interconnection <NUM> in the context of this disclosure is not configured or arranged to be, in use, in contact with human or animal tissue. For example, by embedding the one or more interconnections <NUM> in a low conductance or insulating substrate <NUM>, such as LCP. Note that an interconnection <NUM>, may be comprised in the first <NUM> or second surface <NUM> if it rendered low conductance and/or insulating by including one or more layers between the interconnection <NUM> and any human or animal tissue.

Additionally or alternatively, the substrate <NUM> may be a multilayer, comprising one or more electrical interconnection layers to provide the electrode <NUM> with electrical energy. In use, the electrical interconnections are connected to a source of electrical power (not depicted). If an LCP multilayer is used, the thickness (extent of the substrate <NUM> along the second transverse axis <NUM> or the perpendicular distance between the first surface <NUM> and the second surface <NUM>) may be typically approximately <NUM> (micron) in the sections with no electrodes <NUM> or interconnections, <NUM> in the sections with an electrode <NUM>, and <NUM> in the sections with an electrical interconnection <NUM>. If multilayers are used, electrical interconnection layers of <NUM> (micron) may be used, for example.

In the context of this disclosure, proximal is used to describe proximity to the one or more stimulation electrodes <NUM>, comprised in the implantable end <NUM>.

The one or more proximal return (or ground) electrodes <NUM> are configured to provide, in use, a corresponding electrical return for one or more stimulation electrodes <NUM>. In other words, the electrical return <NUM> closes the electrical circuit. Any suitable configuration and arrangement may be provided. Additionally or alternatively, one or more return (ground) electrodes may be provided proximate the one or more electrodes stimulation electrodes <NUM>, at the implantable end <NUM> of the system <NUM>, <NUM>.

In some descriptions of conventional stimulation devices, the return electrode may be referred to as an anode. Traditionally, this has been provided via the housing of an IPG (Implantable Pulse Generator). Stimulation electrodes may similarly be referred to as cathodes.

The one or more proximal return electrodes <NUM> may comprise a conductive material such as gold, silver, platinum, iridium, and/or platinum/iridium alloys and/or oxides.

Alternatively, the depicted proximal return electrode <NUM> may be functionally described as follows: it comprises two proximal return electrode regions 400a, 400b, electrically connected to each other, the two proximal return electrode regions 400a, 400b being disposed on opposing sides of the one or more stimulation electrode <NUM>. In other words, if the device <NUM> was viewed in a transverse cross-section <NUM>, <NUM> (substantially parallel to the first <NUM> and second <NUM> substantially planar transverse surfaces), the main regions 400a, 400b of the proximal return electrode <NUM> that influence the stimulation current density are disposed directly "above" the one or more stimulation electrodes <NUM> (but further along the second transverse axis <NUM>). In other words, at substantially the same disposition along the first transverse axis <NUM> as the one or more stimulation electrodes <NUM>. The regions 400a, 400b are disposed along the first transverse axis <NUM> approximately proximate (and approximately parallel to) opposing edges of the substrate <NUM>.

The two proximal return electrode <NUM> regions a, b are comprised in a substantially contiguous proximal return electrode <NUM>.

An end (or lead) <NUM> suitable for implanting may comprise, for example, <NUM> stimulation electrodes over a length of <NUM>. Each stimulation electrode may have dimensions in the order of <NUM> to <NUM> along the longitudinal axis <NUM> and <NUM> to <NUM> along the first transverse axis <NUM>, so approximately <NUM> to <NUM> square mm (mm<NUM>). If a strip of <NUM> wide (extent along the first transverse axis <NUM>) is provided as a return electrode, then a length (extent along the longitudinal axis <NUM>) <NUM> to <NUM> also provides a tissue contact-area of <NUM> to <NUM> square mm (mm<NUM>).

<FIG> depicts a view of the second surface <NUM> of the implantable end <NUM> depicted in <FIG>. In other words, the second surface <NUM> is depicted in the plane of the paper, lying along the longitudinal axis <NUM> (depicted from bottom to top) and in the first transverse axis <NUM> (depicted from left to right). The second transverse axis <NUM> extends into the page. This is the view facing the animal or human tissue which is stimulated (in use). The first surface <NUM> is not depicted in <FIG>, but lies at a higher position along the second transverse axis <NUM> (into the page), and is also substantially parallel to the plane of the drawing.

The substrate <NUM> extends along the first transverse axis <NUM> (considered the width of the implantable end <NUM> of the stimulation device) between two extents.

The implantable end <NUM> of the device may be implanted by first creating a tunnel and/or using an implantation tool.

The one or more proximal return electrodes <NUM> are depicted in <FIG>, but not in <FIG>.

After implantation of the implantable end <NUM> of the system <NUM>, <NUM>, a source of stimulation energy may be configured and arranged to provide, in use, electrical energy to the one or more stimulation electrodes <NUM> with respect to the electrical return applied to the one or more return electrodes <NUM>.

By providing one or more proximal return electrodes proximate the one or more stimulation electrodes at substantially the same longitudinal disposition, a substantially transverse electric field may be provided. It may then provide a more concentrated current density and distribution in directions approximately perpendicular to the longitudinal axis (transversely-oriented electric field). This provides an additional degree of configuration for stimulation systems and devices.

<FIG> depict longitudinal cross-sections through an example of a stimulation energy source <NUM>, suitable for use with any of the implantable ends described in this disclosure, including the first example <NUM> depicted in <FIG>. Optionally, the stimulation energy source <NUM> may be configured and arranged to be implantable.

In this example, they are assumed to be comprised in the same substrate <NUM>. The stimulation energy source <NUM> comprises analogous features to those depicted in <FIG>:
the implantable end <NUM> comprises the same features as depicted in <FIG>:.

The dimensions of the substrate <NUM> (extent along the first transverse axis <NUM> or width, extent along the second transverse axis <NUM> or thickness) at the implantable <NUM> and energy source <NUM> ends are depicted as approximately the same. It is convenient if the device <NUM>, <NUM> comprises the same substrate <NUM>, allowing it to be made from a single piece of material - this is advantageous if the implantable end <NUM> of the device is substantially completely implanted as this may reduce the risk of fluid ingress into the device.

The stimulation energy source <NUM> further comprises:.

In the context of this disclosure, distal is used to describe proximity to the pulse energy controller <NUM>, comprised in the stimulation energy source <NUM> and/or close to the energy source <NUM>.

Preferably, the one or more distal return electrodes <NUM> that are to be actively used are comprised in a section of the device that is configured and arranged to be implantable. In addition, during use, the active one or more distal return electrodes <NUM> are preferably implanted so that they may provide a corresponding electrical return for the implanted one or more stimulation electrodes <NUM> that are active.

The one or more distal return electrodes <NUM> may comprise a conductive material such as gold, silver, platinum, iridium, and/or platinum/iridium alloys and/or oxides.

The functions comprised in the pulse energy controller <NUM>, the separation into functional units, and the components used in each functional unit may be any suitable mix to perform the required functions. In terms of the invention, during stimulation operation, the pulse energy controller <NUM> transfers electrical energy to one or more stimulation electrodes <NUM> as one or more electrical stimulation pulses.

The one or more proximal return electrodes <NUM> are configured as a first part of the electrical return <NUM>, <NUM> for the one or more stimulation electrodes <NUM>; and the one or more distal return electrodes <NUM> are configured as a second part of the electrical return <NUM>, <NUM> for the one or more stimulation electrodes <NUM>.

So the electrical return comprises the first part, proximate the one or more stimulation electrodes <NUM> and the second part, distant from (distal) one or more stimulation electrodes.

The pulse energy controller <NUM> further comprising a ratio controller, configured and arranged to modify the electrical ratio of the first part (proximal) of the electrical return to the second part (distal). The ratio controller provides a convenient way to concentrate or diffuse the substantially transverse <NUM>, <NUM> electric field.

The proximal : distal ratio may vary between <NUM> : <NUM> and <NUM> : <NUM>. Expressed in percentages, this is <NUM>% : <NUM>% to <NUM>% : <NUM>%. When one of the parts of the electrical returns is approximately <NUM>, it is substantially disabled and very similar to the situation where those types of electrodes are not connected (or are disconnected).

At <NUM> : <NUM>, the electric field is stronger (more localized in the regions close to the stimulation electrodes). At <NUM> : <NUM>, the electric field is weaker (more global, and distributed through the tissue between the proximal return electrodes <NUM> and the distal electrodes <NUM>).

Stimulation electrodes <NUM>, such as those depicted in <FIG>, may have, for example, a dimension along the longitudinal axis <NUM> (a longitudinal extent) in the order of <NUM> to <NUM>, with a pitch of <NUM> to <NUM> along the longitudinal axis.

An active proximal return electrode <NUM> is most preferably disposed at substantially the same longitudinal disposition as the corresponding active one or more stimulation electrodes <NUM>.

Although less preferred, an active return electrode <NUM> may also be considered proximal if it is disposed within a distance of one stimulation electrode longitudinal extent (for example, <NUM> to <NUM>) from the corresponding active one or more stimulation electrodes <NUM>.

Although even less preferred, an active return electrode <NUM> may also be considered proximal if it is disposed within a distance of two stimulation electrode longitudinal extents (for example, <NUM> to <NUM>) from the corresponding active one or more stimulation electrodes <NUM>.

An active return electrode <NUM> may be considered distal if it is more than three stimulation electrode longitudinal extent (for example, <NUM> to <NUM>) from the corresponding one or more active stimulation electrodes <NUM>.

<CIT> describes more than one return electrodes at different distances from one or more corresponding stimulation electrode. However, in the terms of the invention, these are proximal return electrodes comprised in the implantable end or paddle. It does not describe the combined use of a distal return electrode, comprised in the stimulation energy source, together with a proximal electrode using a predetermined ratio.

<FIG> depicts a simplified electrical diagram of the electrical energy paths through the patient body.

The electrical energy is provided as stimulation pulses from an energy source <NUM> comprised in the pulse energy controller <NUM>. The stimulation pulses are provided to one or more stimulation electrodes <NUM>. Two main paths of stimulation current are created through the patient body:.

As depicted in <FIG>, the ratio controller may be implemented using:.

By coupling together the variable adjustments of the proximal variable resistor <NUM> and the distal variable resistor <NUM>, an increase in one of the resistance values may cause a decrease in resistance of the other, and vice-versa.

Additionally or alternatively, a fixed resistor may be used in one of the paths adjust the ranges of ratio's that may be controlled in this way.

One proximal path <NUM>, <NUM>, <NUM> is depicted in <FIG> - optionally, if more than one active proximal return electrode <NUM> is provided, more than one proximal path <NUM>, <NUM>, <NUM> may also be provided. They may be configured for operation together (in other words, more than one proximal return electrodes <NUM> connected electrically to the same proximal variable resistor <NUM>) or they may be configured to be operated separately (in other words, more than one proximal return electrodes <NUM> connected electrically to more than one proximal variable resistor <NUM>). If configured to be operated separately, the ratio's between different proximal paths may be adjusted - this may be advantageous as it may create a more complex distribution of field densities.

One distal path <NUM>, <NUM>, <NUM> is depicted in <FIG> - optionally, if more than one active distal return electrode <NUM> is provided, more than one distal path <NUM>, <NUM>, <NUM> may also be provided. They may be configured for operation together (in other words, more than one distal return electrodes <NUM> connected electrically to the same distal variable resistor <NUM>) or they may be configured to be operated separately (in other words, more than one distal return electrodes <NUM> connected electrically to more than one distal variable resistor <NUM>). If configured to be operated separately, the ratio's between different distal paths may be adjusted - this may be advantageous as it may create a more complex distribution of field densities.

The variable resistors <NUM>, <NUM> may be linear. One or both may be non-linear. One or both may be logarithmic. Additionally or alternatively, any non-linear or logarithmic behavior may be modified by adapting a user interface to make the adjustments seem more linear to the user. If a digital control system is used, then any required behavior may be provided.

The resistance of human tissue is typically in the range <NUM> kOhm to <NUM> kOhm. Human tissue is highly conductive. The resistance of the paths is less affected by the length of the path through tissue, and affected to a higher degree by the tissue contact area of the electrodes <NUM>, <NUM>.

With pulses of <NUM> (<NUM> microseconds), typical values are:.

<FIG> depicts an alternative simplified electrical diagram of the electrical energy paths through the patient body.

It is the same as the circuit in <FIG>, except for the use of a rheostat <NUM> instead of the variable resistors <NUM> and <NUM>). One end of the rheostat <NUM> is electrically connected to the proximal return electrode <NUM>, and the other side of the rheostat <NUM> is connected to the distal return electrode <NUM>. The tap (or slider) is connected to the electrical return of the pulse energy source <NUM>.

By moving the tap (or slider), an increase in one of the path resistance values is provided at the same time as a decrease in resistance of the other path, and vice-versa.

Variable resistors and/or rheostats <NUM>, <NUM>, <NUM> may result in unwanted heat generation in the pulse energy controller <NUM>.

Alternatively or additionally, a time multiplexer may be used to control the amount of time that each return path <NUM>, <NUM> and <NUM>, <NUM> is connected to the energy source. Such a configuration and arrangement reduces heat generation in the pulse energy controller <NUM>. The longer that a path is connected within a particular period of time, the larger its contribution electrical return. For example:.

Variable resistors <NUM>, <NUM> may also be used in combination with time multiplexer.

Alternatively or additionally, a plurality of (more than one) distal return paths <NUM>, <NUM> may be provided by providing more than one distal return electrodes <NUM>. When the tissue contact area of the return electrodes is maximised, the resistance <NUM> through the patient tissue is mainly determined by the tissue contact surface area of the one or more distal return electrodes <NUM>.

Alternatively or additionally, a plurality of (more than one) proximal return paths <NUM>, <NUM> may be provided by providing more than one proximal return electrodes <NUM>. When the tissue contact area of the return electrodes is maximised, the resistance <NUM> through the patient tissue is mainly determined by the tissue contact surface area of the one or more proximal return electrodes <NUM>.

Alternatively or additionally, the pulse energy controller <NUM> may comprise switches which may switch one or more of the plurality of return paths <NUM>, <NUM> and/or <NUM>, <NUM> into or out of the electrical return circuit to the energy source <NUM>. The time multiplexer described above may be further configured and arranged to switch between the plurality of return paths.

Additionally or alternatively, the one or more return electrodes <NUM>, <NUM> may be increase or reduced in tissue contact area to predetermine the tissue contact area, which may influence the resistance of the return path <NUM>, <NUM> through the body.

Additionally or alternatively, resistive elements may be comprised in the pulse energy controller <NUM>, the one or more interconnections <NUM>, the one or more return electrode <NUM>, <NUM> to predetermine differences in resistance between the return paths <NUM>, <NUM> and <NUM>, <NUM>.

<FIG> depict examples of how the electric field may be configured to vary the strength of the field close to the electrodes. <FIG> depict transverse cross-sections in the plane comprising the first transverse axis <NUM> and the second transverse axis <NUM> through a modified version of the electrodes depicted in <FIG>. As viewed, the longitudinal axis <NUM> is perpendicular to the plane of the drawing (or the plane of the paper), and the direction is emerging. In other words, the transverse cross-section is viewed from an implantable end <NUM> looking towards an energy source <NUM> end.

One or more proximal return electrodes <NUM> are provided, comprised in the first surface <NUM>. One or more stimulation electrodes <NUM> are provided, comprised in the second surface <NUM>.

A corresponding proximal return electrode <NUM> and a stimulation electrode <NUM> are depicted. The proximal return electrode <NUM> is configured as a return (for example, a ground or 0V) for the stimulation electrode <NUM> - if a positive voltage is applied to stimulation electrode <NUM>, an electric field may be provided, in use, in the region between the stimulation electrode <NUM> and the proximal return electrode <NUM>. Examples of lines of equipotential 570a to 570f are also depicted - the first equipotential 570a approximately coincides with the edges of the transverse extent <NUM> of the proximal return electrode <NUM>. This is approximately the same potential as the proximal return electrode <NUM>, here (for example) ground or 0V.

The last equipotential 570f approximately coincides with the edges of the transverse extent <NUM> of the stimulation electrode <NUM>. This is approximately the same potential as the stimulation electrode <NUM>.

Between the first 570a and last 570f equipotential lines, intermediate equipotential lines 570b to 570e are depicted - the distance between the equipotential lines <NUM> increases linearly over the distance "around" the substrate from the transverse edge <NUM> of the proximal return electrode <NUM> to the transverse edge <NUM> of the stimulation electrode <NUM>.

For example, if 5V is applied to the stimulation electrode <NUM>, and the proximal return electrode <NUM> is configured as ground (0V), then the approximate potential at each equipotential line <NUM> is 570a at 0V, 570b at 1V, 570c at 2V, 570d at 3V, 570e at 4V and 570f at 5V.

The transverse disposition <NUM> of the stimulation electrode <NUM> and the proximal return electrode <NUM> are approximately the same, providing a substantially symmetrical electrical field.

The extent along the first transverse axis <NUM> (width) of the corresponding return <NUM> and stimulation <NUM> electrodes is larger in <FIG> than in <FIG>. The first equipotential 570a is substantially disposed at the transverse edge <NUM> of the proximal return electrode <NUM> and the last equipotential 570f is substantially disposed at the transverse edge <NUM> of the stimulation electrode <NUM>. The electrical field is provided between these two edges, "around" the substrate - the disposition difference along the first transverse axis <NUM> and/or the second transverse axis <NUM> determine the derivative of the potential over the distance - the closer the edges, the more local (the stronger) the electric field.

In addition, although not depicted in <FIG>, the relative disposition along the longitudinal axis <NUM> of the edges also determine the longitudinal disposition of the electric field.

Although depicted as substantially symmetrical, the transverse positions of the proximal return <NUM> and stimulation <NUM> electrodes may be asymmetrical to provide a more asymmetrical electric field.

As depicted, the transverse extent <NUM> of the proximal return electrode <NUM> is less than the transverse extent <NUM> of the substrate. By making the transverse extents <NUM> more similar and optionally equal, the first equipotential 570a then approximately coincides with the edges of the transverse extent <NUM> of the substrate.

The devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may further comprise one or more (conventional) stimulation electrodes not having a corresponding proximal return electrode.

Any of the proximal return electrode configurations <NUM>, <NUM>, <NUM>, <NUM> disclosed herein may be combined with any of the stimulation electrode configurations <NUM>, <NUM> disclosed.

From <CIT>, it is known to operate a stimulation device using a combination of return electrodes at different separations from the one or more stimulation electrodes. Although, substantially transverse fields may be created, as depicted in FIG. <NUM> and explained in the corresponding part of the description, the device requires two implantable electrode ends to create a substantially transverse field. This is because the proximal return electrode is not at substantially the same longitudinal disposition in the implantable end as the corresponding stimulation electrode - the lead comprises a sequence of electrodes, some of which may be configured as return electrodes, which creates a substantially longitudinal field. In addition, the return electrode (or anode) may be provided via the housing of the Implantable Pulse Generator (IPG).

In the embodiments described in this disclosure, the use of an elongated substrate <NUM> with stimulation electrodes at substantially the same longitudinal disposition as the one or more proximal return electrodes means that a substantially transverse field may be created using only one lead. When using implanted leads (implantable ends comprising one or more electrodes), a reduction in the number of leads is advantageous.

This may be provided by a tissue stimulation system <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprising:.

the stimulation system further comprising:.

In addition, in the embodiments in this disclosure, the geometric relationships between the one or more stimulation electrodes may be predetermined to a high degree, and are less dependent on the dispositions after implantation. Instead of relying on a distal return electrode that is at least tens of centimeters away (in <CIT>, use is made of the IPG housing), the embodiments in this disclosure use one or more distal return electrodes <NUM> more than three stimulation electrode longitudinal extents (for example, <NUM> to <NUM>) from the corresponding one or more active stimulation electrodes <NUM>. This may improve control of the field density. Additionally, it may also reduce energy loss through the return paths.

As the resistance is mainly dependent on the tissue contact areas of the return electrodes <NUM>, <NUM>, the embodiments in this disclosure may provide return path resistances which may be predetermined to a high degree.

<FIG> depict a second embodiment of an implantable end <NUM>. It is the same as the first embodiment <NUM>, depicted in <FIG> except:.

Similar to the return electrode <NUM> depicted in <FIG>, the longitudinal <NUM> extent of the electrode regions 401a, 401b in <FIG> are approximately the same as the longitudinal <NUM> extent of the corresponding one or more stimulation electrodes <NUM>.

The electrode regions 401a, 401b are least partially disposed along the first transverse axis <NUM> on opposite sides of the lower stimulation electrode <NUM>. In other words, if the device <NUM> was viewed in a transverse cross-section <NUM>, <NUM> (substantially parallel to the first <NUM> and second <NUM> substantially planar transverse surfaces), the regions 401a, 401b of the proximal return electrode <NUM> that influence the stimulation current density are disposed directly "above" (further along the second transverse axis <NUM>) the transverse edges of the one or more stimulation electrode <NUM>.

<FIG> depict a third embodiment of an implantable end <NUM>. It is the same as the second embodiment <NUM>, depicted in <FIG> except:.

As in <FIG>, this proximal return electrode <NUM> has a longitudinal <NUM> extent which approximates the longitudinal <NUM> extent of the one or more stimulation electrodes <NUM>.

The regions 402a, 402b providing the corresponding proximal electrical return are at approximately the same longitudinal disposition <NUM> as their corresponding one or more stimulation electrodes <NUM>.

Similar to proximal return electrode <NUM> in <FIG>, the two electrode regions 402a, 402b of the proximal return electrode <NUM> are disposed on opposing sides of the one or more stimulation electrode <NUM>. Also each return electrode region 402a, 402b is separated at least partially along the first transverse axis <NUM> from the one or more stimulation electrodes <NUM> by an electrical insulator.

<FIG> depict a longitudinal cross-section through an implantable end of a fourth embodiment <NUM>. It is the same as the third embodiment <NUM>, depicted in <FIG> except:.

As in <FIG>, the proximal return electrode <NUM> comprises comprising two electrode regions 403a, 403b electrically connected to each other, through one or more interconnections <NUM>, and configured to provide, in use, a corresponding electrical return for the stimulation electrode <NUM>.

The two electrode regions 403a, 403b are elongated along the longitudinal axis <NUM>, and disposed on opposing sides of the stimulation electrode <NUM>, each electrode region 403a, 403b being separated from the stimulation electrode <NUM> by an electrical insulator (in this case, a separation between the conducting return electrode 403ab and the conducting stimulation electrode <NUM> which have been applied to a very low conducting (and/or very high resistant) substrate <NUM>. Typically, the separation will be in the range <NUM> to <NUM>. Less than <NUM> may also be used, although it may be necessary to compensate for parasitic capacitance.

In general, one or more stimulation electrodes <NUM> may be provided. The number, dimensions and/or spacings of the stimulating electrodes <NUM> may be selected and optimized depending on the treatment - for example, if more than one electrode <NUM> is provided, each electrode <NUM> may provide a separate stimulation effect, a similar stimulation effect or a selection may be made of one or two electrodes <NUM> proximate the tissues where the effect is to be created. The electrodes <NUM> may comprise a conductive material such as gold, silver, platinum, iridium, and/or platinum/iridium alloys and/or oxides.

Although a rectangular cross-section is suggested in <FIG>, any shape may be used, such a square, rectangular, triangular, polygonal, circular, elliptical, oval, and round. Typically, an elongated electrode <NUM> is used to provide stimulation energy along the entire extent - this is advantageous if the position of nerves to be stimulated is difficult to determine precisely.

In practice, the disposition and path of the nerve pathways vary from person-to-person, and it can happen that after implantation, a stimulation device may not function correctly due to misalignment. However, by using an elongated electrode <NUM>, implanted at a significant angle (in some cases, approximately perpendicular), alignment becomes less critical - there is an increased chance that the elongated electrode <NUM> crosses a point in one or more nerve pathways, and the device <NUM> may be used to stimulate that nerve pathway.

In general, the combined active tissue contact-area of the return electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is preferably equal to or more than the active tissue contact area contact-area of the one or more stimulation electrodes <NUM>, <NUM>. The tissue contact-areas to be considered are not the total contact areas, but the contact areas configured to be active during use - typically, this will be the whole (or a large proportion) of the return electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and one or more stimulation electrodes <NUM>, <NUM>.

The stimulation electrode <NUM> may be selected to provide tissue stimulation at a particular disposition - two or more stimulation electrodes <NUM> may be made active if stimulation over a larger area is required and/or at a disposition between the active electrodes <NUM>.

In general, the ratio between the tissue contact area contact-areas does not need to be determined exactly - they are preferably of a similar order of magnitude. For example, it may be sufficient if the combined active tissue contact area of the one or more return electrodes is equal to or more than <NUM>% to <NUM>% of the active tissue contact area of the one or more stimulation electrodes <NUM>, <NUM>.

An implantable device with an end (or lead) suitable for implant may comprise, for example, <NUM> stimulation electrodes over a length of <NUM>. A stimulation electrode may have dimensions in the order of <NUM> to <NUM> along the longitudinal axis <NUM> and <NUM> to <NUM> along the first transverse axis <NUM>, so approximately <NUM> to <NUM> square mm (mm2). If a strip of <NUM> wide (extent along the first transverse axis <NUM>) is provided as a return electrode, then a length (extent along the longitudinal axis <NUM>) of <NUM> to <NUM> also provides a tissue contact-area of <NUM> to <NUM> square mm (mm2). The electric field is more concentrated between the strip (elongated electrode) and the corresponding stimulation electrode <NUM>, <NUM>.

<FIG> depict examples of nerves that may be stimulated using a suitably configured implantable ends <NUM>, <NUM>, <NUM>, <NUM> to provide neurostimulation to treat, for example, headaches or primary headaches. Providing suitably configured proximal return electrodes <NUM>, means that the stimulation current density in substantially transverse directions <NUM>, <NUM> may be increased, providing an improved stimulation along a longitudinal axis of one or more nerves or nerve branches.

<FIG> depicts the left supraorbital nerve <NUM> and right supraorbital nerve <NUM> which may be electrically stimulated using a suitably configured device. <FIG> depicts the left greater occipital nerve <NUM> and right greater occipital nerve <NUM> which may also be electrically stimulated using a suitably configured device.

Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the distal part of the stimulation device comprising stimulation devices <NUM>, <NUM>, <NUM>, <NUM> are depicted as regions:.

In many cases, these will be the approximate locations <NUM>, <NUM>, <NUM>, <NUM> for the implantable device <NUM>, <NUM>, <NUM>, <NUM>.

For each implant location, <NUM>, <NUM>, <NUM>, <NUM> a separate stimulation system may be used. Where implant locations <NUM>, <NUM>, <NUM>, <NUM> are close together, or even overlapping, a single stimulation system may be configured to stimulate at more than one implant location <NUM>, <NUM>, <NUM>, <NUM>.

A plurality of stimulation devices <NUM>, <NUM>, <NUM>, <NUM> may be operated separately, simultaneously, sequentially or any combination thereof to provide the required treatment.

<FIG> depict further examples of nerves that may be stimulated using a suitably configured improved implantable device <NUM>, <NUM>, <NUM>, <NUM> to provide neurostimulation to treat other conditions. As in <FIG>, the ability to increase the stimulation current density in transverse directions <NUM> improves the stimulation along a longitudinal axis of the nerve or nerve branches. The locations depicted in <FIG> (<NUM>, <NUM>, <NUM>, <NUM>) are also depicted in <FIG>.

Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the part of the stimulation device comprising stimulation electrodes are depicted as regions:.

Other condition that may be treated include gastro-esophageal reflux disease and inflammatory diseases.

The descriptions thereof herein should not be understood to prescribe a fixed order of performing the method steps described therein. Rather the method steps may be performed in any order that is practicable. Similarly, the examples are used to explain the algorithm, and are not intended to represent the only implementations of these algorithms - the person skilled in the art will be able to conceive many different ways to achieve the same functionality as provided by the embodiments described herein.

In general, for any of the configurations described and depicted in this disclosure, any electrode <NUM>, <NUM> may be connected as either a stimulating <NUM> or return electrode <NUM>. This may be advantageous if it is uncertain whether the implantable end is above or below the targeted tissue - for example, above or below a nerve. This may be advantageous if it is uncertain whether the implantable end is above or below the targeted tissue - for example, above or below a nerve.

Claim 1:
A tissue stimulation system (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising an implantable end (<NUM>, <NUM>, <NUM>, <NUM>) and a stimulation energy source (<NUM>), the implantable end (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
- an elongated substrate (<NUM>, <NUM>), disposed along a longitudinal axis (<NUM>), the substrate having a first (<NUM>) and second (<NUM>) surface disposed along substantially parallel transverse planes (<NUM>, <NUM>);
- one or more stimulation electrodes (<NUM>, <NUM>), comprised in the second surface (<NUM>) and configured to transmit energy, in use, to human or animal tissue; and
- one or more proximal return electrodes (<NUM>, <NUM>, <NUM>, <NUM>), comprised in the first surface (<NUM>) or second surface (<NUM>), disposed proximate the one or more stimulation electrodes (<NUM>, <NUM>);
the stimulation energy source (<NUM>) comprising:
- one or more distal return electrodes (<NUM>), disposed distantly from the one or more stimulation electrodes (<NUM>, <NUM>); and - a pulse energy controller (<NUM>);
the tissue stimulation system (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) further comprising:
- one or more interconnections (<NUM>) between the implantable end (<NUM>, <NUM>, <NUM>, <NUM>) and a stimulation energy source (<NUM>), configured and arranged to connect the output of the pulse generator (<NUM>) to the one or more stimulation electrodes (<NUM>) whereby electrical energy may be transferred, during use, as one or more electrical stimulation pulses to the one or more stimulation electrodes (<NUM>, <NUM>) with respect to an electrical return (<NUM>, <NUM>);
wherein:
- the one or more proximal return electrodes (<NUM>, <NUM>, <NUM>, <NUM>) are configured as a first part of the electrical return (<NUM>, <NUM>) for the one or more stimulation electrodes (<NUM>, <NUM>); and
- the one or more distal return electrodes (<NUM>) are configured as a second part of the electrical return (<NUM>, <NUM>) for the one or more stimulation electrodes (<NUM>, <NUM>);
the pulse energy controller (<NUM>) further comprising a ratio controller, configured and arranged to modify the electrical potential and/or current ratio of the first part to the second part.