Mitigation of MRI RF-induced heating for SCS aimds

Abstract

The present disclosure relates to an implantable lead system, comprising: a first lead comprising a first electrical conductor for delivering current to a first electrode; a second lead comprising a second electrical conductor for delivering current to a second electrode; wherein at least one of the first and second electrical conductors is coiled; and wherein the first and second leads are adapted to be arranged essentially adjacent to each other in a patient, such that the first and second electrical conductors inductively couple to each other. Furthermore, the present disclosure relates to an implantable lead system, comprising: a first lead comprising a first electrical conductor for delivering current to a first electrode; a second lead comprising a second electrical conductor for delivering current to a second electrode; wherein the first and second electrodes are adapted to be arranged essentially adjacent to each other in a patient; and wherein the electrical pathlengths of the first and second electrical conductors are different from each other.

Description

[0001] Mitigation of MRI RF-induced heating for SCS AIMDs

[0002] TECHNICAL FIELD

[0003] The present invention generally relates to implantable lead systems and implantable medical devices with such lead systems, for example neurostimulators. The present invention also relates to methods and computer programs for optimizing implantable lead systems.

[0004] BACKGROUND

[0005] Medical devices, such as implantable medical devices (IMDs) have gained significant importance in recent years. Non-limiting examples of IMDs include pacemakers, defibrillators, pressure sensors, neurostimulators, or the like. Thus, IMDs enjoy a wide range of applications. Furthermore, the demand for IMDs is expected to increase significantly as the value of IMDs is expected to become even more important in the future. Such an increased demand may be fueled by new medical technologies evolving that enable new potentials for IMDs, and this may include medical technologies not deemed realistic as from today’s viewpoint.

[0006] Implantable medical devices are often active devices (AIMDs) that require electrical power. Often power is supplied by wires that extend along substantial distances within the patient’s body.

[0007] However, such wires may make the AIMDs prone to substantial heating, e.g. when the patient undergoes treatment with external electromagnetic waves, such as used during MRI (magnetic resonance imaging). Tissue surrounding the AIMDs or their wires, respectively, may excessively heat up causing (permanent) damage, such that MRI imaging may not be possible anymore after implantation. There have been various approaches to cope with this issue. However, the approaches used so far do not deliver optimal results. Hence there is a need to further address this issue.

[0008] SUMMARY

[0009] According to various aspects outlined herein, the above need is met at least in part.

[0010] A first aspect relates to an implantable electrode lead system, comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode; a second electrode lead comprising a second electrical conductor for delivering current to a second electrode; wherein at least one of the first electrical conductor and second electrical conductor is coiled; and wherein the first electrode lead and second electrode lead are adapted to be arranged essentially adjacent to each other in a patient, such that the first electrical conductor and second electrical conductor inductively couple to each other.

[0011] The first electrode lead and the second electrode lead may thus be configured such that an inductive coupling between the first electrical conductor and second electrical conductor can be enabled when the first electrode lead and second electrode leads are essentially arranged adjacent to each other in a patient.

[0012] The inductive coupling may, for example, be induced by an electromagnetic wave the first electrode lead and the second electrode lead are exposed to. In an example, the inductive coupling may be induced by an (characteristic) electromagnetic wave (as described herein) having a frequency in a range from 1 MHz to 300 MHz. For example, the (characteristic) electromagnetic wave may stem from an MRI (magnetic resonance imaging) treatment the implantable electrode lead system is exposed to (e.g., together with the patient). For example, the (characteristic) electromagnetic wave may stem from an RF electrical field from an MRI-apparatus’ RF coil. The (characteristic) electromagnetic wave may induce a first electrical field around the first electrode lead and a second electrical field around the electrode second lead. For example, electrical field lines may originate from the electrodes or electrical conductors of the electrode leads such that an electrical field is generated around the respective electrode lead. Furthermore, the first electrical field may be associated with a first voltage standing wave being present at the first electrode lead, and the second electrical field may be associated with a second voltage standing wave being present at the second electrode lead.

[0013] The enabled inductive coupling between the electrode leads may cause an increased impedance for the electrode leads. In turn, this may increase a voltage drop along the length of the electrode leads. The voltage drop may then cause suppression of the voltage standing wave (or electrical field) induced in each electrode lead body by the incident (characteristic) electromagnetic wave.

[0014] Due to this suppression effect a power dissipation around the electrode leads may be minimized at least in part. Namely, as the implantable electrode leads may be positioned within a patient, the suppression effect may ensure that no harmful power is dissipated over the patient’s tissue.

[0015] According to the present disclosure the electrode leads of the electrode lead system are therefore adapted (e.g., at least when residing within the patient’s body) to ensure that the inductive coupling may enable the described suppression effect. For example, this may be ensured by accordingly positioning the electrode leads of the implantable electrode lead system within the patient, wherein the electrode leads have respective electrical properties (e.g., electrical pathlengths) to ensure the suppression effect.

[0016] In an example of the first aspect, the first electrical conductor and / or the second electrical conductors may comprise an average number of windings per cm in the range of 1 to 5. For example, the first electrical conductor and / or second electrical conductor may comprise an average number of windings per cm of 1, 2, 3, 4 or 5. It has been found out that within this range a suitable suppression effect may be achieved. In an example of the first aspect, the at least one of the first electrical conductor and the second electrical conductor may be coiled with a coil diameter in the range of 0.2 mm to 2 mm, wherein particularly within this range a suitable suppression effect may be achieved. Notably, the according coil shape of a coiled electrical conductor may also be referred to herein as a helix shape. The coil diameter may also be referred to herein as helix diameter. In some examples, the coil diameter may be below 1 mm.

[0017] The coil diameter (helix diameter) may be regarded as a characteristic width of the coil shape (or helix shape). For example, the coil diameter may comprise the outer diameter of the respective coil (or helix). In another example, the coil diameter may comprise the mean diameter of the respective coil (or helix). In a further example, the coil diameter may comprise the mean diameter of the respective coil (or helix).

[0018] In an example of the first aspect, the first electrode lead and the second electrode lead may be adapted to be arranged essentially adjacent to each other, such that the closest distance between the first electrical conductor and the second electrical conductor is within the range of 0.5 mm to 15 mm.

[0019] For example, the first electrode lead and the second electrode leads may be adapted to be arranged essentially adjacent to each other, such that the closest distance between the first electrical conductor and the second electrical conductor is shorter than a diameter of the spinal cord of the patient.

[0020] In an example of the first aspect, the first electrode lead and the second electrode lead each may comprise a plurality of electrical conductors, each electrical conductor for delivering current to a corresponding electrode. For example, the first electrode lead may comprise two or more electrical conductors for delivering current to respective two or more electrodes of the first electrode lead, and wherein the second electrode lead may comprise two or more electrical conductors for delivering current to respective two or more electrodes of the second electrode lead. For example, each electrode of an electrode lead may have a corresponding electrical conductor for delivering current to it. Hence, if an electrode lead may have eight electrodes, the electrode lead may have (at least) eight electrical conductors, as well, with each electrical conductor being able to couple current to a respective electrode.

[0021] In an example, the first electrode lead may comprise three or more electrical conductors (for coupling to three or more respective electrodes), wherein the second electrode lead may comprise three or more electrical conductors (for coupling to three or more respective electrodes). In an example, the first electrode lead may comprise five or more electrical conductors (for coupling to five or more respective electrodes), wherein the second electrode lead may comprise five or more electrical conductors (for coupling to three or more respective electrodes). In an example, the first electrode lead may comprise eight or more electrical conductors (for coupling to eight or more respective electrodes), wherein the second electrode lead may comprise eight or more electrical conductors (for coupling to eight or more respective electrodes).

[0022] A second aspect relates to an implantable electrode lead system, comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode; a second electrode lead comprising a second electrical conductor for delivering current to a second electrode; wherein the electrical pathlengths of the first and second electrical conductors are different from each other. In an example of the second aspect, the first electrode and second electrode (or the first and second electrode lead) are adapted to be arranged essentially adjacent to each other in a patient.

[0023] Notably, the disclosure with respect to the first aspect may also apply to the herein described second aspect. In an example, the implantable electrode lead system of the second aspect further comprises features described herein for the implantable electrode lead system of the first aspect. The same applies vice versa. The disclosure with respect to the second aspect may also apply to the herein described first aspect. In an example, the implantable electrode lead system of the first aspect further comprises features described herein for the implantable electrode lead system of the second aspect. A main concept of the implantable electrode lead system according to the second aspect is that the electrical pathlengths of the first and second electrical conductors are different. Hence, the first electrical conductor may have a first electrical path length, and the second electrical conductor may have a second electrical pathlength, wherein the first electrical pathlength is different from the second electrical pathlength. This may enable purposefully manipulating electrical fields that are induced around each lead due to an electromagnetic wave being applied to the electrode lead system.

[0024] As described herein, a (characteristic) electromagnetic wave may induce a first electrical field around the first electrode lead and a second electrical field around the second electrode lead. For example, the (characteristic) electromagnetic wave may cause a scattered electrical field at each electrode lead. The electrical field lines may originate from the electrodes (or electrical conductors) of the electrode leads such that an electrical field is generated around the respective electrode lead. Furthermore, the first electrical field may be associated with a first voltage standing wave being present at the first electrode lead, and the second electrical field may be associated with a second voltage standing wave being present at the second electrode lead. The electrical fields may cause a form of power dissipation over a patient’s tissue when the electrode lead system is implanted into the patient’s body.

[0025] With the implantable electrode lead system (according to the second aspect) having different electrical pathlengths regarding the electrode leads the interactions between the first and second electrical field may be optimized to reduce power dissipation into a patient’s tissue.

[0026] For example, a relative phase velocity of a (voltage) standing wave at an electrode lead may change due to an adaptation of the electrical pathlength of the electrode lead. Particularly, this mechanism may be used to adapt the interaction between the first and second electrical field to a patient’s advantage. Namely, due to the different electrical pathlength difference it may be enabled that the two leads have different relative phase velocities. For example, the first electrode lead may then have a first relative phase velocity, wherein the second electrode lead may then have a second relative phase velocity which is different from the first relative phase velocity.

[0027] This difference in relative phase velocities may then cascade down to the relative phases of the electrical fields. Hence, by having different electrical pathlengths the relative phase between the first and second electrical field may be adapted.

[0028] For example, the difference in electrical pathlengths in the implantable electrode lead system of the second aspect may be chosen such that a desired relative phase is achieved between the first and second electrical fields. For example, the desired relative phase may be chosen to locally tune the power dissipation onto the patient’s tissue to a desired state. Furthermore, the relative phase may be chosen to minimize the overall power dissipation onto the patient’s tissue at least in part.

[0029] In an example of the second aspect, when a (characteristic) external electromagnetic wave (as described herein) is applied to the first and second electrode lead, a first electrical field may be induced around the first electrode lead and a second electrical field may be induced around the second electrode lead, wherein, due to the different electrical pathlengths of the first and second electrical conductors, a region of destructive interference of the first and second electrical field is generated between the first and second electrode lead.

[0030] In this example, by using the herein-described mechanisms for adapting the relative phase between the first and second electrical field via the pathlength difference a region of destructive interference may be purposefully tailored. Notably, the region of destructive interference may be positioned by the pathlength difference such that it is between the first and second electrode lead. In an example, the region of destructive interference may be positioned by the pathlength difference such that it is between an electrode of the first electrode lead and an electrode of the second electrode lead. By way of this approach, it may be ensured that a region between the electrode leads has a reduced power dissipation since the electrical field strength in the region of destructive interference is reduced compared to a region where no (significant) destructive interference occurs. This may ensure that at least in the region of destructive interference a power dissipation onto a patient’s tissue may be adapted onto desirable levels such that no harm may be caused to the patient.

[0031] For example, the first and second electrode leads of the electrode lead system may be placed into a patient’s body for enabling electrical stimulation of nerve cells via the electrodes of the electrode leads. The electrode lead system may function as part of an electrical stimulator to that regard. Hence, the electrode leads may be placed around or onto nerve cells. Hence, nerve cells may be present between the two electrode leads or at least in a vicinity of a line between the first electrode lead and the second electrode lead. For example, the electrode leads may be placed at a spinal cord such that at least a part of the spinal cord may be present between the two electrode leads, or a part of the spinal cord may be in a vicinity of a line between first and second electrode lead.

[0032] By enabling the region of destructive interference between the first electrode lead and the second electrode lead, potential nerve cells between the first and second electrode lead may thus be protected since the region of destructive interference may constitute a region where less power is dissipated.

[0033] In an example of the second aspect, due to the different electrical pathlengths of the first electrical conductor and the second electrical conductor: a relative phase difference between the first and second electrical field may be between 5° and 45°; and / or an effective electrical field within the region of destructive interference may be substantially zero.

[0034] Particularly, a relative phase difference of 5° to 45° may be particularly advantageous for medical applications. Furthermore, a relative phase difference of 10° to 45°, more preferably between 15° to 45° may also enable desired conditions regarding the power dissipation. As described, such relative phase differences may be purposefully generated via the electrical pathlength difference.

[0035] Notably, the difference in electrical pathlengths may also be chosen such that an electrical field within the region of destructive interference is substantially zero. Hence, a spot may be generated between the first electrode lead and the second electrode lead where substantially no power dissipation occurs to protect the patient’s tissue.

[0036] In an example of the second aspect, the (characteristic) external electromagnetic wave has a frequency in the range from 1 MHz to 300 MHz, preferably a frequency of 64 MHz and / or 128 MHz. For example, the (characteristic) electromagnetic wave may stem from an MRI (magnetic resonance imaging) treatment the implantable electrode lead system is exposed to (together with the patient). For example, the (characteristic) electromagnetic wave may stem from an RF electrical field from an MRI-apparatus’ RF coil.

[0037] In an example, the (characteristic) external electromagnetic wave has a frequency in the range from 16 MHz to 300 MHz, preferably 50 MHz to 300 MHz, more preferably 64 MHz to 300 MHz.

[0038] In an example of the second aspect, the pathlength difference may be adapted such that a relative phase difference between an electric field induced by an electromagnetic wave having a frequency in the range from 16 MHz to 256 MHz at the first electrode and at the second electrode leads to an effective field of substantially zero at a distance of about 1 mm to 10 mm from a line connecting the first and second electrodes.

[0039] In an example the first electrical conductor and the second electrical conductor do not comprise any shielding.

[0040] In an example of the first and / or second aspect, the first electrode lead may have two or more electrical conductors for delivering current to respective electrodes of the first electrode lead, and the second electrode lead may have two or more electrical conductors for delivering current to respective electrodes of the second electrode lead, wherein for each electrode lead the two or more electrical conductors are arranged in a co-radial arrangement.

[0041] Notably, the concept of co-radial arrangement of electrical conductors is known. Due to the herein described aspects, power dissipation may be addressed via the electrical pathlength difference (or the inductive coupling arrangement) such that a less complicated co-radial arrangement of electrical conductors may be implemented. Furthermore, the co- radial arrangement may enable a more reliable implementation of a desired pathlength difference since respective influencing parameters of the co-radial arrangement may be easily configured (as described herein).

[0042] In an example of the first and / or second aspect the first electrode lead may have two or more electrical conductors for delivering current to respective electrodes of the first electrode lead, and the second electrode lead may have two or more electrical conductors for delivering current to respective electrodes of the second electrode lead, wherein for each electrode lead the two or more electrical conductors are not arranged in a co-axial arrangement.

[0043] In view of the herein described aspects power dissipation may be addressed via the electrical pathlength difference (or the inductive coupling arrangement) such that a more complicated co-axial arrangement of electrical conductors may be avoided. For example, a co-axial arrangement may constitute a more complex structure than a co-radial arrangement, where it may be more difficult to implement a desired pathlength difference.

[0044] In an example of the first and / or second aspect the first electrical conductor of the first electrode lead and the second electrical conductor of the second electrode lead may differ in at least one of the following: a) when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a pitch of the first helix shape is different from a pitch of the second helix shape; b) when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a handedness of the first helix shape may be different from a handedness of the second helix shape; c) when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a helix diameter of the first helix shape may be different from a helix diameter of the second helix shape; d) when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a wire diameter of the first electrical conductor may be different from a wire diameter of the second electrical conductor; and / or e) the first electrical conductor may be wound in a helix shape and the second electrical conductor may be arranged as or comprise a substantially straight wire within the second electrode lead.

[0045] Notably, also other differences may be implemented to achieve a difference in electrical pathlength between the first and second lead.

[0046] Subsequently, the examples are discussed in more detail.

[0047] For example, when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a pitch of the first helix shape is different from a pitch of the second helix shape. As is known, the pitch of a helix is the height of one complete helix turn measured parallel to the axis of the helix. For example, the first electrical conductor and the second electrical conductor may be wound in a co-radial arrangement in a helix shape in their respective electrode leads, wherein the first electrical conductor comprises a first helix pitch, and the second electrical conductor comprises a second helix pitch different from the first helix pitch.

[0048] For example, the first and second helix pitch may differ by at least 5 %, 10 %, 50 %, 100 % or 200 %.

[0049] For example, when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a handedness of the first helix shape may be different from a handedness of the second helix shape. For example, the first helix shape may be right-handed, wherein the second helix shape may be lefthanded (or vice versa).

[0050] For example, when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a helix diameter of the first helix shape may be different from a helix diameter of the second helix shape. The helix diameter may comprise any type of helix diameter (or coil diameter) as described herein. For example, the first electrical conductor may have a first helix diameter, wherein the second electrical conductor may a second helix diameter which is different from the first helix diameter.

[0051] For example, the first and second helix diameter may differ by at least 5 %, 10 %, 50 % or 100 %.

[0052] For example, when the first electrical conductor is wound in a first helix shape and the second electrical conductor is wound in a second helix shape, a wire diameter of the first electrical conductor (first wire diameter) may be different from a wire diameter of the second electrical conductor (second wire diameter). For example, the first helix shape may be made out of a thicker wire than the second helix shape.

[0053] For example, the first wire diameter of the first helix shape and the second wire diameter of the second helix shape may differ by at least 5 %, 10 %, 50 %, 100 %, 200% or 300 %.

[0054] In an example, the first electrical conductor may be wound in a helix shape and the second electrical conductor may be arranged as a substantially straight wire within the second electrode lead. For example, each of the first electrode lead and the second electrode lead may have two or more electrical conductors. One electrode lead may have helix shape electrical conductors, the other electrode lead may have straight wires as electrical conductors. The straight wires may be spaced at different distances within the electrode lead body to give different electrical lengths. Furthermore, the straight wire diameter may be changed to give different electrical lengths. For example, the wire diameter of the straight wire may be different from the wire diameter of the electrical conductor in the helix shape. Also, in an electrode lead having two or more straight wires, a first wire may have a different diameter than a second wire to adapt the electrical pathlength of the respective electrode lead with respect to the electrical pathlength of the other lead.

[0055] Notably, the herein described differences between the first and second electrical conductors may be combined. For example, when the first electrical conductor is wound in a first helix shape and the second conductor is wound in a second helix shape, a pitch of the first helix shape is different from a pitch of the second helix shape, and a handedness of the first helix shape may be different from a handedness of the second helix shape. In another example, when the first electrical conductor is wound in a first helix shape and the second conductor is wound in a second helix shape, a pitch of the first helix shape is different from a pitch of the second helix shape, and a wire diameter of the first electrical conductor may be different from a wire diameter of the second electrical conductor.

[0056] A third aspect relates to an implantable electrode lead system, comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode, a second electrode lead comprising a second electrical conductor for delivering current to a second electrode wherein the first and second electrode lead are adapted to be arranged essentially adjacent to each other in a patient such that the first electrode lead and the second electrode lead essentially parallelly extend along a common direction, and the first electrode is arranged offset the second electrode with respect to the common direction.

[0057] Particularly, the disclosure with respect to the first aspect or second aspect may also apply to the herein described third aspect. In an example, the implantable electrode lead system of the third aspect further comprises features described herein for the implantable electrode lead system of the first aspect and / or second aspect. The same applies vice versa. The disclosure with respect to the first aspect or the second aspect may also apply to the herein described third aspect. In an example, the implantable electrode lead system of the first aspect further comprises features described herein for the implantable electrode lead system of the third aspect. In an example, the implantable electrode lead system of the second aspect further comprises features described herein for the implantable electrode lead system of the third aspect.

[0058] A main concept of the implantable electrode lead system according to the third aspect is that by an offset arrangement of one or more electrodes of one electrode lead and one or more electrodes of another electrode lead, particularly in the implanted state. This may enable purposefully manipulating or adjustment of electrical fields that are induced around each lead due to an electromagnetic wave being applied to the electrode lead system.

[0059] As already described above, an electromagnetic wave may cause a scattered electrical field at each electrode in both leads. When adjacent electrodes of both leads are parallelly aligned along the common direction of extension, i.e. the adjacent electrodes are not arranged offset each another, the relative phase between the scattered electrical fields is zero. By an offset arrangement of two adjacent electrodes the relative phase the scattered electrical fields of two adjacent electrodes may adjusted, which in turn may alter the location at which an electrical cancelation occurs, particularly to a location between the adjacent electrodes. Particularly, the relative phase between the scattered electrical fields may be adjusted to value between 5 degrees and 45 degrees by the offset arrangement of adjacent electrodes of both electrode leads, respectively.

[0060] With the implantable electrode lead system (according to the third aspect) having an offset arrangement of two adjacent electrodes (of different leads) the interactions between the first and second electrical field may be optimized to reduce power dissipation into a patient’s tissue.

[0061] In an example of an implantable electrode lead system according to the third aspect, the first electrode lead comprises a first plurality of first electrodes including a distal first electrode, the second electrode lead comprises a plurality of second electrodes including two distal second electrodes, wherein the first distal electrode of the first electrode lead is arranged between the two distal second electrodes of the second electrode lead with respect to the common direction. In an example of an implantable electrode lead system according to the third aspect, the first electrode lead comprises a first plurality of first electrodes, e.g. eight electrodes, include a first distal electrode, a first proximal electrode and a number of first intermediate electrodes (e.g. six electrodes) arranged between the first distal electrode and the first proximal electrode, the second electrode lead comprises a second plurality of electrodes, e.g. eight electrodes, include a second distal electrode, a second proximal electrode and a number of second intermediate electrodes (e.g. six electrodes) arranged between the first distal electrode and the first proximal electrode, wherein particularly each of the first plurality of first electrodes is arranged offset to a corresponding second electrode of the second plurality of second electrodes. In an example, the first distal electrode of the first electrode lead may be arranged between the second distal electrode and an adjacent second intermediate electrode with respect to the common direction. In an example, the second proximal electrode may be arranged between the first proximal electrode. In an example, each of the first intermediate electrode is arranged between a second intermediate electrode and another second intermediate electrode, the distal second electrode or the proximal second electrode.

[0062] A fourth aspect relates to an implantable medical device, in particular a neurostimulator, comprising an electrode lead system according to the first and / or second aspect. For example, the implantable medical device may comprise a pulse generator for generating electrical pulses which may be coupled to the electrical conductors of the herein described electrode lead systems.

[0063] In an example, the implantable medical device may comprise a neurostimulator wherein the neurostimulator comprises a spinal cord stimulator (SCS).

[0064] In an example, the implantable medical device may further comprise the first electrode and the second electrode. The first and second electrode may be coupled to the electrical conductors of the respective lead system such that the electrical pulses of the pulse generator may be coupled to the electrodes for delivery onto a patient’s tissue. In an example, the implantable medical device may further be configured such that the first electrode and the second electrode are positionally fixed with respect to each other.

[0065] A fifth aspect relates to a method for optimizing an implantable electrode lead system, the implantable electrode lead system comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode; and a second electrode lead comprising a second electrical conductor for delivering current to a second electrode; wherein the method comprises the steps: determining electric fields induced by an electromagnetic wave having a frequency in the range from 1 MHz to 300 MHz such that a first electrical field is generated around the first lead and a second electrical field is generated around the second lead to determine a position of destructive interference of the first and second electrical field; and adapting an electrical pathlength of the first and / or second electrical conductor such that the position of the destructive interference is shifted to a target position which lies between the first electrode lead and the second electrode lead.

[0066] The determining may, for example, comprise simulating the electrical fields via an according simulation (e.g., based on a finite element method). The determining may, for example, also comprise measuring respective parameters to determine the region of constructive interference.

[0067] The frequency may preferably be between 50 MHz and 150 MHz.

[0068] Thus, by the approach of the fourth aspect the parameters needed for a desired electrical pathlength difference may be determined. For example, it may be simulated what characteristics a helix shape of the first electrical conductor should have compared to a helix shape of the second electrical conductor to place the region of destructive interference at a desired location. A sixth aspect relates to a method for optimizing an implantable electrode lead system, the implantable lead system comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode; and a second electrode lead comprising a second electrical conductor for delivering current to a second electrode; wherein the method comprises the steps: determining electric fields induced by an electromagnetic wave having a frequency in the range from 1 MHz to 300 MHz such that a first electrical (e.g., voltage) standing wave is generated around the first lead and a second electrical (e.g., voltage) standing wave is generated around the second lead to determine a relative phase velocity of the first electrical standing wave and a relative phase velocity of the second electrical standing wave.

[0069] In an example, the method may comprise adapting the electrical pathlength difference between the first and second electrical conductor such that a relative phase between the first and second electrical field is between 5° and 45°. The approach of the fifth aspect may be combined with the approach of the fourth aspect (and vice versa).

[0070] A seventh aspect relates to a computer program comprising code with instructions which, when executed, cause a computer to perform the steps of the method of the fourth aspect.

[0071] Whether described as method steps, computer program and / or means, the functions described herein may be implemented in hardware, software, firmware, and / or combinations thereof. If implemented in software / firmware, the functions may be stored on or transmitted as one or more instructions or code on a computer-readable medium.

[0072] Computer-readable media include both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, FPGA, CD / DVD or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general -purpose or special-purpose computer, or a general-purpose or special-purpose processor.

[0073] The methods as described herein may also be implemented in hardware, software, firmware, and / or combinations thereof, for example, by means of one or more general- purpose or special-purpose computers, and / or a general-purpose or special-purpose processors.

[0074] DESCRIPTION OF THE DRAWINGS

[0075] In the following, preferred embodiments are described, by way of example only. Reference is made to the following accompanying figures:

[0076] Fig. 1 : shows an exemplary implantable electrode lead system according the present invention connected to a stimulation device in an implanted state in the area of the spine of a patient;

[0077] Fig. 2: show examples of an electrode lead system that may be used for an implantable medical device according to the present disclosure, such as spinal cord stimulators;

[0078] Fig. 3: shows an example for a section of an electrode lead system according to the present disclosure, particularly a dual electrode lead system;

[0079] Fig. 4: shows an exemplary electrode lead system of an implantable medical device according to the present disclosure, wherein a superposition of electric fields induced in the electrode leads by a radiofrequency electromagnetic wave impinging on the electrode lead system is shown, as determined by finite element simulation; Fig. 5: shows another example for a section of an electrode lead system, particularly a dual electrode lead system, wherein the electrode lead system is configured such that an electrical path difference between the first lead and second electrode lead is present;

[0080] Fig. 6: shows another example for a section of an electrode lead system, particularly a dual electrode lead system, wherein the electrode lead system is configured such that an electrical path difference between the first electrode lead and second electrode lead is present; and

[0081] Fig. 7 shows an exemplary electrode lead system of an implantable medical device according to the present disclosure.

[0082] DETAILED DESCRIPTION

[0083] In the subsequent passages, the invention is described with reference to the accompanying figures in more detail. It is noted that further embodiments are certainly possible, and the below explanations are provided by way of example only, without limitation.

[0084] While specific feature combinations are described with respect to the exemplary embodiments of the present invention, it is to be understood that not all features of the discussed embodiments have to be present for realizing the invention, which is defined by the subject matter of the claims. The disclosed embodiments may be modified by combining certain features of one embodiment with one or more features of another embodiment. Specifically, the skilled person will understand that features, components and / or functional elements of one embodiment can be combined with technically compatible features, components and / or functional elements of any other embodiment of the present invention given that the resulting combination falls within the definition of the invention provided by the claims. The skilled person also understands that certain features may be omitted in so far as they appear dispensable. Throughout the present figures and specification, the same reference numerals refer to the same elements. The figures may not be to scale, and the relative size, proportions, and depiction of elements in the figures may be exaggerated for clarity, illustration, and convenience.

[0085] Fig. 1 shows a patient P with an exemplary implantable medical device 1 for neurostimulation of nerve cells. In the example of Fig. 1 the implantable medical device 1 may be designed a spinal cord stimulator SCS 1 for neurostimulation of nerve cells in a spinal cord and / or spinal column W of the patient. However, the implantable medical device 1 may also be any other type of device for neurostimulation of nerve cells. Subsequently, the functionalities of the implantable medical device 1 according to the present disclosure is explained with respect to a spinal cord stimulator SCS 1. The SCS 1 may comprise a generator 7 that may generate electric stimuli to be applied to the spinal cord W of patient P. The SCS 1 may further comprise a connector 9 (e.g., comprised within a header) for delivering the electric stimuli from generator 7 to an electrode lead system 5, according to the present disclosure.

[0086] The electrode lead system 5 may comprise a first electrode lead 5a and a second electrode lead 5b, as described herein. An electrode lead 5a, 5b may comprise one or more electrical conductors 171, 17b. Notably, the first electrode lead 5a and second electrode lead 5b may be configured as two separate electrode leads having two separate paths at least over a certain length (e.g., in the form of two separate “cables”, as for example shown in Fig. 2b). However, the first 5a and second electrode lead 5b may also partly be configured such that they are guided into a common distal end portion 3a, 3 b, particularly designed in form of a paddle (e.g. as shown in Figs. 2A). .

[0087] Notably, the herein described aspects of the electrode lead systems 5 may in particular apply to the characteristics of the electrode lead system 5 in the area of the electrode system 3. The herein described effects of the lead systems 5 may thus occur in particular in the area of the electrode system. As described, the electrode system 3 may be configured to apply electrical stimuli generated by generator 7 via two electrode leads 5a, 5b them to nerve cells of the patient (e.g., to the spinal cord) via the one or more electrodes I la, 11b. To that regard, the two electrode leads 5a, 5b may comprise one or more electrical conductors 17a, 17b, each for delivering a stimulus, e.g. in the form of a current and / or voltage pulse, to a corresponding electrode.

[0088] Figs. 2A B show various exemplary electrode configurations 3a, 3b of the electrode system 3 and their coupling to the electrode lead system 5, that may be particularly used by a spinal cord stimulator 1.

[0089] Fig. 2A shows a top view of a first electrode configuration 3a. Electrodes I la, 11b are arranged on a flattened carrier element 13. However, in an alternative example, the electrodes I la, l ln may be arranged on a curved carrier element (e.g., a VNS collar paddle). Subsequently, the concept of the first electrode configuration 3a is described with respect to a flattened carrier element 13, as shown in Fig. 2A. Electrodes 11 of first electrode configuration 3a may be positionally fixed with respect to each other. Electrode configuration 3a may form a paddle-electrode 13. Each electrode I la, 11b may comprise an electrode surface 15 which may be adapted to contact tissue of a patient, such that electrical stimuli can be applied to the tissue.

[0090] Electrodes I la, 11b of first electrode configuration 3a may be arranged in two sets of electrodes I la, 11b (a first set I la shown on the left side in Fig. 2A, a second set 11b shown on the right side in Fig. 2A). Electrodes I la, 11b may be arranged in pairs of electrodes 1 la, 1 lb, wherein each pair comprises a first electrode I la being part of the first set of electrodes and a second electrode 1 lb being part of the second set of electrodes.

[0091] Each electrode I la, 11b may separately be provided with stimuli (electrical energy form generator 7) by means of its own electrical conductor 17a, 17b connecting it to a generator 7, wherein, two leads 5a, 5b may be provided to guide the electrical conductors 17a, 17b of the first set I la and second set 11b of electrodes to a generator 7. Moreover, electrode configuration 3a may comprise a flattened (or curved) carrier element 13 on which electrodes 1 la, 1 Iba may be arranged.

[0092] In the example of Figs. 2 A, two sets of electrodes 11, 11b, each set having 8 electrodes 11 are provided. Correspondingly, two electrode leads 5a, 5b are provided, each lead having 8 electrical conductors 17a, 17b. In other examples, different numbers of electrodes 11 and / or conductors 17a, 17b may be provided per electrode set / lead.

[0093] Fig. 2B shows a different electrode configuration 3b. Therein, two separate electrode leads 5a, 5b (without common distal end section supporting the electrodes I la, 11b) are placed substantially adjacent to each other. For each electrode lead 5a, 5b, a single set of electrodes I la, 11b is provided (at the distal ends of at the electrode leads). The first electrode lead 5a has a first set of electrodes I la, the second electrode lead 5b has a second set of electrodes 11b. Each electrode I la, 11b may be coupled to a generator by an individual electrical conductor 17a, 17b. For example, the first electrode lead 5a may have eight electrical conductors 17a (not shown in Fig. 2B), wherein each electrical conductor 17a is coupled to a respective electrode I la of the first electrode lead 5a. The second electrode lead 5b may also have eight electrical conductors 17b, wherein each electrical conductor 17b is coupled to a respective electrode 11b of the second electrode lead 5b. in the two electrode leads 5a, 5b may, for example, be individually coupled to the generator 7. In the exemplary configuration 3b, eight electrodes I la, 11b are provided for each electrode lead 5a, 5b. These may be arranged positionally fixed with respect to each other, e.g. on a rod like element which may optionally be rotationally symmetric.

[0094] This arrangement achieves a similar effect as with electrode configurations 3a within the patient at a certain distance the same (or similar) opposing electrode configuration 3b may be achieved as shown for Figs. 2A. Hence, when implanting electrode configuration 3b, a further degree of freedom is provided which, on the one hand, provides more flexibility, but on the other hand may also cause more efforts.

[0095] Regardless of the electrode configuration, medical devices as described herein may have in common that they comprise an electrode lead system 5, e.g. a dual lead system, wherein a first electrode lead5a and a second electrode lead 5a (depicted as one lead 5 in Fig. 1) are arranged adjacent to each other after implantation at least at the distal end of the electrode leads 5a, 5b supporting the electrodes I la, 11b , as shown in Fig. l.The skilled person will appreciate that the first and second electrode lead 5a, 5b not necessarily have to follow the spinal canal or epidural space, respectively, as depicted in Fig. 1. The first and second electrode lead 5a, 5b may follow a more arbitrary routing, for example, in case of the electrode lead system 5 comprises a flattened (or curved) carrier element 13 at the distal end, e.g., as disclosed in Fig. 2A).

[0096] Fig. 3 shows a zoomed in view of a longitudinal section 300 of an electrode lead system 5, according to the present disclosure. A first electrode lead 5a of the electrode lead system 5 may comprise a first electrode lead body with an outer element, such as an outer tube 10a. A second electrode lead 5b of the electrode lead system 5 may comprise a second lead body with an outer element, such as an outer tube 10b. The outer elements 10a, 10b of the first and second electrode leads 5a, 5b may be substantially similar or identical. The first electrode lead 5a and the second electrode lead 5b may be spaced apart by a spacing distance D.

[0097] In the example of Fig. 3, each electrode lead 5a, 5b comprises 8 electrical conductors 17a, 17b. In other examples, a different number of electrical conductors 17a, 17b may be provided, wherein preferably both electrode leads 5a, 5b comprise the same number of electrical conductors 17a, 17b. One or more of the electrical conductors 17a, 17b of at least one electrode lead 5a, 5b (in the example of Fig. 3: all of the electrical conductors) may be coiled. The one or more electrical conductors 17a, 17b may by coiled substantially identically, as shown in Fig. 3. In Fig. 3, the eight electrical conductors 17a, 17b of each strand are coiled to form co-radial windings of all eight electrical conductors 17a, 17b.

[0098] The co-radial windings may enable an inductive coupling C between the two electrode leads 5a, 5b when the characteristic electromagnetic wave F impinges onto the leads 5a, 5b. As described herein, the characteristic electromagnetic wave F may stem from an MRI- imaging. For example, the electromagnetic wave F may induce a first (scattered) electrical field at the first electrode lead 5a and a second (scattered) electrical field at the second electrode lead 5b. Hence, a superposition of the first and second electrical field may occur. The first and second electrical field may cause a certain amount of power dissipation to occur throughout the patient’s tissue.

[0099] The inductive coupling C may occur since the co-radial conductor windings store magnetic energy, which may be shared and / or may effect an opposition with the co-radial conductors 17, 17b of the adjacent electrode lead 5a, 5b and vice-versa via a transformer action. To that regard, an electrode lead system 5 having coil-radial windings in both electrode leads 5 a, 5b may be regarded as a transformer, wherein the transformer action ensures an inductive coupling leading to an optimized power dissipation (e.g., a minimized power dissipation).

[0100] Furthermore, the co-radial windings of the electrode leads 5a, 5b may ensure that an impedance of the electrode leads 5a, 5b is increased, leading to an increased voltage drop along the length of the electrode leads 5a, 5b. This then causes suppression of the voltage standing wave induced in each lead body by the incident RF electrical field from the MRI RF coil. Power dissipation onto a patient’s tissue in the vicinity of the electrode leads 5, a 5b may thus be minimized at least in part. Hence, an idea of the present disclosure may be regarded as ensuring inductive coupling, while also increasing the impedance of the leads such that the electrical field around the electrode leads 5a, 5b caused by the characteristic electromagnetic wave F is suppressed.

[0101] In other examples, only the electrical conductors 17a, 17b within an electrode lead 5a, 5b may be coiled identically, but the coiling of the electrical conductors 17a of the first electrode lead 5a may differ from that of the electrical conductors 17b, of the second electrode lead 5b. This may lead to different electrical pathlengths for the electrode leads 5a, 5b. For example, the helix shape of the electrical conductors 17a in the first electrode lead 5a may differ from the helix shape of the electrical conductors 17b in the second electrode lead 5b such that the first electrode lead 5a has a different electrical pathlength than the second electrode lead 5b (cf. Fig. 5). As described herein, different relative phases velocities may be induced in the electrode leads 5a, 5b due to the different electrical pathlengths. This may induce a relative phase difference between the first electrical field induced at the first electrode lead 5a and the second electrical field induced at the second electrode lead 5b which may be (further) beneficial to ensure a more limited power dissipation throughout the tissue.

[0102] For example, when the electrical conductors 17a, 17b of the first and second electrode lead 5a, 5b are formed as helixes, the first electrode lead 5a may have a first helix pitch and the second electrode lead 5b may have a second helix pitch different from the first helix pitch. For example, the second helix pitch may deviate from the first helix pitch by at least 5 %, at least 10 %, at least 20 % or at least 30 %. In another example, the second helix pitch may deviate from the first helix pitch by no more than 5 %, 10 %, 20 % or 30 %. In another example, the lead system may be configured such that a ratio of the second helix pitch (Hl) with respect to the first helix pitch (H2) - which may be termed H2 / H1 - is different from one (H2 / H1 1).

[0103] The coiling may be implemented by means of an inner element, such as an inner tube 20a, 20b, wherein the electrode leads 5a, 5b may each comprise an essentially similar or identical inner tube 20a, 20b. The electrical conductors 17a, 17b may be coiled around inner tube 20a, 20b. An outer diameter of inner tube 20a, 20b may thus approximately fix a coiling diameter of the electrical conductors I la, 1 lb.

[0104] Furthermore, Fig. 3 also shows a coil vector V which indicates how the electrical conductor 17a, 17b is oriented along the electrode lead 5a, 5b with respect to its longitudinal main direction. For example, the coil vector may be (substantially) identical for the first and second electrode leads 5a, 5b. However, the coil vector may also be different for the electrode leads 5, 5b which may ensure a desired electrical pathlength difference (as described herein).

[0105] Fig. 4 shows an example electrode lead system 5 of an implantable medical device 1 according to the present disclosure, wherein a superposition of electric fields induced in the leads by a radiofrequency electromagnetic wave impinging on the electrode lead system 5 is shown, as determined by finite element simulation.

[0106] As described herein, the electromagnetic wave may induce a first (scattered) electrical field at the first electrode lead 5a and a second (scattered) electrical field at the second electrode lead 5b. Hence, a superposition of the first and second electrical field may occur.

[0107] In particular, Fig. 4 shows the effect of 0° relative phase between the scattered E-fields from the two adjacent electrodes I la, 11b where a clear region of destructive interference 430 can be seen between the adjacent electrodes I la, 11b. The position of the destructive interference 430 can be changed by manipulating the relative phase of the scattered E-field from the adjacent electrodes 11. For example, for SCS applications, the spinal cord may be located ventral relative to the SCS electrode lead electrodes I la, 11b. Therefore, a region of destructive interference, placed in the region of the spinal cord may minimize RF power deposition in the spinal cord. According to the present disclosure this may be enabled by choosing an according electrical path difference between the two electrode leads 5a, 5b. This may be adapted by choosing different properties for the electrical conductors in the first and second electrode lead 5a, 5b (as described herein). The different properties may be estimated analytically (e.g., via a simulation) or experimentally, such that the required relative phase for SCS applications is between 5 degrees and 45 degrees (as described herein). Preferably, the required relative phase for SCS applications may be between 5 degrees and 45 degrees.

[0108] For example, by adapting the electrical path difference between the first and second electrode lead 5a, 5b the region of the destructive interference may be shifted to a desired target position. Furthermore, the region of destructive interference may also be altered such that an overall power dissipation may be minimized.

[0109] Notably, the term electrical path length (or electrical path) of the present disclosure may also be regarded as the electrical length (as is known for the person skilled in the art). The effects of the inductive coupling C are subsequently shortly described. To that regard the leads of the electrode lead system 5 can be abstracted as being a system of respective windings (such that both electrode leads 5a, 5b may be regarded as a transformer). In general, a self-inductance of a winding can be expressed as L. The inductive reactance is given by XL = coL, where co is the frequency expressed in rad / s. Technically, co is the angular velocity, which is a function of frequency, where co = 27tf, where f is the frequency in Hz. As is evident, inductance is independent of frequency, whereas inductive reactance is frequency dependent.

[0110] Similarly, in the case of inductive coupling (in a transformer action) a mutual inductance M is given. As above, the mutual inductance M is independent of frequency, whereas mutual inductive reactance is frequency dependent. The higher the frequency, the greater the “mutual inductive reactance”.

[0111] In a typical transformer, a source is connected to a primary winding and a load is connected to a secondary winding such that the source and load are electrically isolated from each other, but still behave as a single circuit due to magnetic coupling.

[0112] For illustration purposes the windings in the first electrode lead 5a may be considered to be the primary windings, and the windings in the second electrode lead 5b may be considered to be the secondary windings of a transformer. It is evident in such an example that both the primary and secondary windings are connected to their respective source and loads. Notably, the sources are identical because both leads 5a, 5b are exposed to similar incident field from the MRI RF coil. The loads may also be regarded as similar. In such a case, the mutual reactance may enable to reduce the respective source powers to the respective loads.

[0113] Due to the frequency dependence of mutual reactance, the reactance is significantly greater at MRI frequencies in the MHz range (e.g., 64 MHz or 128 MHz) as compared to therapeutic frequency in the khZ range (e.g., 10 kHz), wherein the therapeutic frequency may be a frequency at which electrical stimuli are applied over the electrodes of the herein described implantable medical device (e.g., an SCS). Hence, by having a (comparatively) higher (mutual) reactance a suppression of induced currents from an MRI RF field (in the MHz range) is significantly more pronounced than suppression of therapeutic signals (occurring in the kHz range).

[0114] A concept of the herein described aspects may thus be regard to increase the reactance since this may block the effects caused by an electromagnetic wave in the MHz range.

[0115] Furthermore, it is subsequently described how the position of the region of desired destructive interference can be determined in view of the teachings of the present disclosure.

[0116] Firstly, in a given electrode lead system 5 the underlying electrical path length or path length differences of the leads may be determined by using S-parameters on a network analyzer (e.g., S21 measurements).

[0117] Furthermore, determining the region of the constructive interference (in view of the phase differences of the first and electrical fields of the electrode lead system 5) can be based on using respective simulations. In such a simulation the cancellation effect between the electrical fields may be a smooth function. Changing the phase difference would increase the smoothness of the transition. The path difference required for a desired phase difference may be determined via simulations that would take into account at least one of the following: the insulation material of the leads, the surrounding tissue of the leads, the lead characteristics. The region of constructive interference would further be dependent on a given frequency of the characteristic electromagnetic wave.

[0118] For example, the required conductor lengths to achieve a 15 degree to 45 degree phase difference may depend on the frequency of the characteristic electromagnetic wave.

[0119] Fig. 5 shows another example for a section 500 of an electrode lead system 5, wherein the electrode lead system 5 is configured such that an electrical path difference between the first electrode lead 5a and second electrode lead 5b is present. In particular Fig. 5 shows an example, where the pitch difference of the helically shaped electrical conductors 17a, 17b of the electrode leads 5a, 5b ensures an electrical path difference between the two leads. The pitch of the electrical conductors 17a of the first electrode lead 5a is different than the pitch of the electrical conductors 17b of the second lead 5b. In other words, the pitch of the co-radial windings in one lead body is reduced, relative to the other. This would result in one lead body containing an increased number of turns of the co-radially placed conductors relative to the other. The resulting increase in inductive reactance and electrical length of the conductors 17a, 17ab in one lead body would result in a reduction in phase velocity of the MRI RF induced standing wave in that lead body, relative to the other. This change in phase velocity would cascade down to the relative phases of the scattered E-field at the electrode, thereby shifting the position of the destructive interference as desired.

[0120] Furthermore, Fig. 5 also shows the outer tubes 10a, 10b as described in Fig. 3.

[0121] Fig. 6 shows another example for a section of an electrode lead system 5, wherein the electrode lead system 5 is configured such that an electrical path difference between the first electrode lead 5a and the second electrode lead 5b is present.

[0122] In the example of Fig. 6, the electrical conductors 17a, 17b of the electrode leads 5a, 5b are both coiled in a helix shape. However, the helix shapes differ in their handedness. Namely, the electrical conductors 17a of the first electrode lead 5a have a left-handed helix shape, the electric conductors 17b of the second electrode lead 5b have a right-handed helix shape. By this approach a desired inductive coupling C may be ensured (as described herein). Furthermore, the different handedness of the helix shapes may cause a desired electrical pathlength difference between the first electrode lead 5a and the second electrode lead 5b. As described herein, this difference may enable to position a region of constructive interference between the electrode leads 5a, 5b onto a desired position. Fig. 6 also indicates the coil vector V for the electrical conductors 17a, 17b of the first and second electrode lead 5a, 5b. It can be seen that due to the different handedness of the helix shapes the coil vector V also differs for both leads accordingly.

[0123] Fig. 7 shows another example for a section of an electrode lead system 5, wherein the electrode lead system 5 is configured to allow an arrangement of the electrode leads 5a, 5b adjacent to each other in the patient such that adjacent electrodes I la, 11b (one electrode I la first electrode lead 5a, and one electrode 1 lb on the second electrode lead 5b) arranged offset along a common direction R along which both electrode leads 5a, 5b extend. Particularly both electrode leads 5a, 5a may be spaced from one another by, for example, 2mm, and arranged offset, e.g., 3.5mm along the common direction R. By that, the electrodes I la of the first electrode lead 5a, are arranged between two adjacent electrodes 11b of the second electrode lead 5b (except the most proximal electrode I la of the first electrode lead 5b). Likewise, the electrodes 1 lb of the second electrode lead 5a (except the most distal electrode 11b of the second electrode lead 5b), are arranged between two adjacent electrodes 1 la of the first electrode lead 5a.

[0124] Particularly, the offset arrangement results in an adjustment of the relative phase of the scattered electrical fields between two adjacent electrode I la, 11b of the electrode leads 5a, 5b, respectively, wherein particularly a location of an electrical field cancellation may be advantageously altered.

[0125] Notably, the aspects described in this disclosure may, in particular, be useful for an SCS AIMD (Spinal Cord Stimulator - Active Implantable Medical Device). Namely, it can be enabled that an overall reduction in the MRI RF induced voltage standing waves in the leads of an SCS AIMD can occur. Furthermore, a manipulation of relative phase velocities of the MRI RF induced voltage standing waves in the adjacent leads of an SCS AIMD can be enabled to enable selective placement of RF power deposition nulls corresponding to the location of the spinal cord relative to the lead electrodes at the MRI RF frequencies. MRI RF induced heating for SCS AIMDS may thus be mitigated. It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teaching. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention.

Claims

CLAIMS1. Implantable electrode lead system (5), comprising: a first electrode lead (5a) comprising a first electrical conductor (17a) for delivering current to a first electrode (I la); a second electrode lead (5b) comprising a second electrical conductor (17b) for delivering current to a second electrode (1 lb); wherein at least one of the first electrical conductor (17a) and second electrical conductors (17b) is coiled; and wherein the first electrode lead (5a) and the second electrode lead (5b) are adapted to be arranged essentially adjacent to each other in a patient, such that the first electrical conductor (17a) and second electrical conductor (17) inductively couple to each other.

2. Implantable electrode lead system (5) according to claim 1, wherein the first electrical conductor (17a) and / or the second electrical conductor (17b) comprises an average number of windings per cm in the range of 1 to 5.

3. Implantable electrode lead system (5) according to claim 1 or 2, wherein the at least one of the first electrical conductor (17b) and / or the second electrical conductor (17b) is coiled with a coil diameter in the range of 0.2 mm to 2 mm.

4. Implantable electrode lead system (5) according to any of claims 1 to 3, wherein the first electrode lead (5a) and the second electrode lead (5b) are adapted to be arranged essentially adjacent to each other, such that the closest distance between the first electrical conductor (17a) and the second electrical conductor (17b) is within the range of 0.15 mm to 15 mm.

5. Implantable electrode lead system (5) according to any of claims 1 to 4, wherein the first electrode lead (5a) and second electrode lead (5b) each comprises a plurality of electrical conductors (17a, 17b), each electrical conductor (17a, 17b) for delivering current to a corresponding electrode (I la, 1 lb).

6. Implantable electrode lead system (5), comprising: a first electrode lead (5a) comprising a first electrical conductor (17a) for delivering current to a first electrode (I la); a second electrode lead (5b) comprising a second electrical conductor (17b) for delivering current to a second electrode (1 lb); wherein the first electrode (I la) and second electrode (11b) are adapted to be arranged essentially adjacent to each other in a patient; and wherein the electrical pathlengths of the first electrical conductor (17a) and the second electrical conductor (17b) are different from each other.

7. Implantable electrode lead system (5) according to claim 6, wherein, when an external electromagnetic wave is applied to the first electrode lead (5a) and the second electrode lead (5b), a first electrical field is induced around the first electrode lead (5a), and a second electrical field is induced around the second electrode lead (5b), wherein, due to the different electrical pathlengths of the first electrical conductor (17a) and the second electrical conductor (17b), a region of destructive interference of the first and second electrical field is generated between the first electrode lead (5a) and the second lead electrode lead (5b).

8. Implantable electrode lead system according to claim 7, wherein, due to the different electrical pathlengths of the first electrical conductor (17a) and the second electrical conductor (17b): a relative phase difference between the first and second electrical field is between 5° and 45°; and / or an effective electrical field within the region of destructive interference is substantially zero.

9. Implantable electrode lead system (5) according to claim 7 or 8, wherein the external electromagnetic wave has a frequency in the range from 1 MHz to 300 MHz, preferably a frequency of 64 MHz and / or 128 MHz.

10. Implantable electrode lead system (5), comprising: a first electrode lead (5a) comprising a first electrical conductor (17a) for delivering current to a first electrode (I la); a second electrode lead (5b) comprising a second electrical conductor (17b) for delivering current to a second electrode (1 lb); wherein the first electrode (I la) and second electrode (11b) are adapted to be arranged essentially adjacent to each other in a patient; wherein the first electrode lead (5a) and the second electrode lead (5b) are adapted to be arranged essentially adjacent to each other in a patient such that the first electrode lead (5a) and the second electrode lead (5b) essentially parallelly extend along a common direction (R), and the first electrode (I la) is arranged offset the second electrode (1 lb) with respect to the common direction (R).

11. Implantable electrode lead system (5) according to claim 10, wherein the first electrode lead (5a) comprises a first plurality of first electrodes (I la) including a distal first electrode (I la), the second electrode lead (5) comprises a plurality of second electrodes (11b) including two distal second electrodes (1 lb), wherein the first distal electrode (I la) of the first electrode lead (5a) is arranged between the two distal second electrodes (1 lb) of the second electrode lead (5b) with respect to the common direction (R).

12. Implantable electrode lead system (5) according to any of claims 1 to 11, wherein: the first electrode lead (5a) has two or more electrical conductors (17a) for delivering current to respective electrodes (I la) of the first electrode lead (5a), and the second electrode lead (5b) has two or more electrical conductors (17b) for delivering current to respective electrodes (1 lb) of the second electrode lead (5b); wherein for each electrode lead (5a, 5b) the two or more electrical conductors (17a, 17b) are arranged in a co-radial arrangement.

13. Implantable electrode lead system (5) according to any of claims 1 to 12, wherein: the first electrode lead (5a) has two or more electrical conductors (17a) for delivering current to respective electrodes (I la) of the first electrode lead (5a), and the second electrode lead (5b) has two or more electrical conductors (17b) for delivering current to respective electrodes (1 lb) of the second electrode lead (5b); wherein for each electrode lead (5a, 5b) the two or more electrical conductors (17a, 17b) are not arranged in a co-axial arrangement.

14. Implantable electrode lead system (5) according to any of claims 1 to 13, wherein the first electrical conductor (17a) of the first electrode lead (5a) and the second electrical conductor (17b) of the second electrode lead (5b) differ in at least one of the following: a) when the first electrical conductor (17a) is wound in a first helix shape and the second electrical conductor (17b) is wound in a second helix shape, a pitch of the first helix shape is different from a pitch of the second helix shape; b) when the first electrical conductor (17a) is wound in a first helix shape and the second electrical conductor (17b) is wound in a second helix shape, a handedness of the first helix shape is different from a handedness of the second helix shape; c) when the first electrical conductor (17a) is wound in a first helix shape and the second electrical conductor (17b) is wound in a second helix shape, a helix diameter of the first helix shape is different from a helix diameter of the second helix shape; d) when the first electrical conductor (17a) is wound in a first helix shape and the second electrical conductor (17b) is wound in a second helix shape, a wire diameter of the first electrical conductor is different from a wire diameter of the second electrical conductor; and / or e) the first electrical conductor (17a) is wound in a helix shape and the second electrical conductor (17b) is arranged as a substantially straight wire within the second electrode lead (5b).

15. Implantable medical device, in particular a neurostimulator, comprising an implantable electrode lead system (5) according to any of claims 1 to 14.

16. Method for optimizing an implantable electrode lead system, the implantable electrode lead system comprising: a first electrode lead comprising a first electrical conductor for delivering current to a first electrode; and a second electrode lead comprising a second electrical conductor for delivering current to a second electrode; wherein the method comprises the steps: determining electric fields induced by an electromagnetic wave having a frequency in the range from 1 MHz to 300 MHz such that a first electrical field is generated around the first lead and a second electrical field is generated around the second lead to determine a position of destructive interference of the first and second electrical field; adapting an electrical pathlength of the first and / or second electrical conductor such that the position of the destructive interference is shifted to a target position which lies between the first and second lead.

17. Computer program comprising code with instructions which, when executed, cause a computer to perform the steps of the method of claim 16.

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