Magnetic stimulation coil system

Abstract

A Magnetic Stimulation (MS) coil system 2 for connection to a current pulse generator comprising: at least one coil 4 winding for delivering a magnetic field to a target zone of a body; a first and se

Description

BACKGROUND The present invention relates to the field of Magnetic Stimulation (MS), and preferably Transcranial Magnetic Stimulation (TMS). Magnetic stimulating of neuromuscular tissue is well known and comprises a stimulating coil made up of one or more windings, each having a plurality of turns which may generate a succession of electrical discharge pulses producing magnetic pulses which further induce electrical signals in the tissue. Such a coil arrangement is disclosed in US6179770 where the magnetic stimulator generally comprises a charging circuit, a capacitor, a discharge control and a winding which is of a size and power rating appropriate for the generation of magnetic fields sufficient to cause neuromodulation of a body portion. The individual winding or plurality of windings may be size adapted to fit partly over the cranium of a human patient in many applications, as well as being used for stimulation of other body parts. The coil arrangement including windings acts as an inductor and when connected to a stimulator which includes the capacitor provides an input voltage to the inductor which creates a circuit that passes an out of phase, sinusoidal voltage and current through the or each winding. An intense sinusoidal magnetic field is formed near the winding and is used to stimulate neurons in test subjects for medical and research applications. The type of the pulse applied to the coil may not necessarily be sinusoidal, for example, it may be square, rectangular, semi-rectangular, step-like or pulse width modulated. The stimulator is not necessarily an LC circuit and may be based on power electronic converters. An example of a coil arrangement is presented in Figure 1 which shows a double winding coil arrangement presented without a covering that may suitably be positioned on a subject’s body. The windings are made up of a single wound conductive element formed into the double winding configuration which is connected to the stimulator (not shown in Figure 1). Under normal operation for application of a MS treatment current pulses are passed through each winding in opposite directions to generate a focussed magnetic field for application to a target zone. The induced field is strengthened in the zone at which adjacent windings are closest to one another. A problem exists however in being able to modify the coil arrangement quickly and effectively for a designated stimulation protocol without providing an alternative stimulating coil which is both impractical and expensive. Aspects of the present disclosure set out to provide a solution to address this problem, or at least provide a useful alternative. SUMMARY Aspects of the present disclosure are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims. According to an aspect of the present disclosure, there is provided a Magnetic Stimulation (MS) coil system for connection to a current pulse generator, the MS coil system comprising: at least one coil winding for delivering a magnetic field to a target zone of a body; - a first and second adaptor for providing a current pathway from the stimulator to the at least one coil winding for delivering current pulses to the at least one coil winding, the first and second adaptors being releasably engageable between a stimulator and the at least one coil winding independently of one another; - wherein the first adaptor is arranged to enable current flow in a first direction around the coil winding, and the second adaptor is arranged to enable current flow in a second opposite direction around the coil winding. The adaptors each provide an interface between a stimulator and the at least one winding. Each adaptor can therefore be positioned between the stimulator and the at least one winding. Each adaptor is selectable by a user dependent on the treatment or stimulation protocol required, and therefore enable the MS coil arrangement to be operated in multiple different operable modes. A significant advantage of the present invention is the ability to simply swap out the adaptor without having to reset the coil position, where this is typically time consuming and requires precise positioning at the required treatment location. The at least one coil winding is beneficially wound from an elongate conductive element. If there are multiple windings each may be made from an individual elongate conductive element. The MS coil system preferably comprises a first and second coil winding each independently releasably engageable with the first or second adaptor. The provision of a first and second winding allows for a greater number of modes of operation of a MS coil system. For example, it is possible to operate the defined MS coil system with multiple windings in a ‘sham’ or ‘placebo’ mode. The first and second windings are beneficially in a side-by-side configuration. The first direction is beneficially a clockwise direction around the first winding, and the second opposite direction is an anticlockwise direction around the second winding. The first adaptor is beneficially arranged to engage with the first winding such that the current flow direction in the first winding is in the first direction, and the first adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is in a second opposite direction. This results in an increase in the magnetic field strength compared to the magnetic field strength generated by the first and second windings alone. The first and second windings are therefore beneficially positioned relative to one another such that the magnetic field generated by each of the first and second windings combine in a region between the two windings. The second adaptor is beneficially arranged to engage with the first winding such that the current flow direction in the first winding is in the first direction, and the second adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is also in the first direction. This results in the magnetic field generated by each of the first and second windings alone at least partially cancelling thereby enabling the second adaptor to be used for a sham or placebo treatment. This provides a significant benefit in that a patient will still feel a treatment sensation on the scalp, however the magnetic field will not penetrate with sufficient filed intensity to provide any treatment effect. Alternatively, the first direction may be clockwise and the second direction may be anticlockwise, wherein the second adaptor may be arranged to engage with the first winding such that the current flow direction in the first winding is in the anticlockwise direction, and the second adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is in the clockwise direction. This set-up enables operation in a normal treatment mode however allows for alternate flow direction and therefore enables switching between posterior to anterior (PA) and anterior to posterior (AP) pulse waveforms. This is useful for recording differences in latency responses where research has shown that latency exceeding a predetermined threshold is indicative of certain conditions, for example Alzheimer’s. This functionality therefore removes the need to rotate the MS coil arrangement through 180 degrees which is awkward to do and may lead to inaccurate positioning of the MS coil arrangement relative to a patient’s head. It will be understood that two options are presented for alternative second adaptors, however a MS system may be provided that includes both alternative versions of the second adaptor. The first direction is preferably clockwise and the second direction is preferably anticlockwise, wherein the MS coil arrangement preferably further comprises a third adaptor arranged to engage with the first winding such that the current flow direction in the first winding is in the anticlockwise direction, and the third adaptor is preferably arranged to engage with the second winding such that the current flow direction in the second winding is in the clockwise direction. It will be understood that all references to first and second directions are in relation to the directions around the windings. The first and second adaptor each preferably define a current pathway from: a first terminal from a stimulator to a second terminal connected to the first winding; - a third terminal from the first winding to a fourth terminal to the second winding; a fifth terminal from the second winding to a sixth terminal to a stimulator. The second, third, fourth and fifth terminal of the first and second adaptors may comprise sockets. These terminals may be configured such that it is impermissible to incorrectly connect the winding(s) to the adaptor due, for example, to specific engagement formations for each terminal and / or specific markings. This enables ease of switching between different adaptors. The MS coil system preferably further comprises a stimulator for emitting current pulses to the at least one winding. The MS coil system preferably comprises a Transcranial Magnetic Stimulation (TMS) system. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of this disclosure will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which: Figure 1 shows a schematic perspective view of a known coil arrangement represented in two forms wherein Figure la also shows the direction of current flow through the two windings and Figure lb shows the conductive element that connects to a MS stimulator. Figure 2a and b are schematic representations of an MS coil system according to an illustrative embodiment of the present disclosure showing a single winding. Figure 3a-d are schematic representations of an MS coil system according to illustrative embodiments of the present disclosure utilising two windings, illustrating four alternative operable configurations. Figure 4 is a representation of computational modelling of the magnetic field strength for two operable modes. Figure 5 is an illustrative embodiment of the present disclosure with the coil winding(s) incorporated into a cap arrangement. Figure 6 is a schematic illustration of the different effects of the operable modes of the embodiments presented in Figures 3a and 3c respectively. DETAILED DESCRIPTION Embodiments of this disclosure are described in the following with reference to the accompanying drawings. Referring to Figure 1(a) there is a standard known MS coil arrangement 2 used for TMS treatment. The arrows indicated in Figure 1(a) identify the direction in which the current travels through the coil arrangement and the turns of the winding at an instant in time. It will be appreciated that the first winding 4 is wound radially outwardly to inwardly and extends via a bridge portion 5 to a second winding 6 comprising a plurality of turns which is wound in the opposing direction, radially inwardly to radially outwardly. As shown in Figure 1(b), the first and second windings 4, 6 are formed of a single elongate conductive element which extends by having neck 10 to a stimulator including power source (not shown). The power source is incorporated into a stimulator and includes a capacitor that provides an input voltage which resonates passing an out of phase sinusoidal voltage and current through the first and second windings 4, 6. An intense magnetic field is formed near the winding that is used to stimulate neurons in subjects for medical and research applications. Also, the stimulator can serve as a power source using power electronic converters instead of a resonance LC circuit. Referring to Figure 2a and b embodiments of a MS coil system 2 are presented according to the present disclosure. Figure 2a shows a single winding 4 formed by a helically wound elongate conductive element. The winding 4 is shown schematically here for simplicity, however the turns of the winding 4 are preferably but not essentially in the same plane as for example shown in Figure 1. The winding 4 is housed within a housing 12. Also shown in Figure 2a is an adaptor 16(a or b) with terminals 20, 22 for releasable connection to ends 24, 26 of the winding 4. The terminals 20, 22 may be in the form of sockets and the ends 24,26 may be in the form of plugs. This enables ease of switching between different adaptors 16. The adaptor 16(a or b) itself is releasably connectable to a stimulator 3 at terminals 28,29 and can be located within the stimulator housing or externally thereof. Arrows 30a and b show the current flow direction in a first mode of operation with a first adaptor 16a in Figure 2a, and in a second mode of operation using a second adaptor 16b as shown in Figure 2b. The difference between the first and second adaptors 16a and 16b will be appreciated comparing Figures 2a and 2b. The conductive pathway through the adaptor is different, meaning that there is a current pathway between terminal 28 and 20 and also terminal 22 and 29 in Figure 2a, and between terminal 28 and 22 and also 20 and 28 in Figure 2b. This causes reversal of current flow direction through the winding 4. Accordingly, the operable mode may be selected by the user. The difference in operable mode can be understood with respect to Figure 6. Although shown is a double winding MS coil 2, the principle is the same. The selection of different adaptors enables change in the current flow direction through the winding(s) for alternate flow direction and therefore enables switching between posterior to anterior (PA) and anterior to posterior (AP) pulse waveforms. Pulse waveforms in either the PA or AP configuration can activate distinct groups of neurons, as shown in Figure 6. This is also useful for recording differences in latency responses where research has shown that latency exceeding a predetermined threshold is indicative of certain conditions, for example as biomarkers for Alzheimer’s disease. This functionality of adaptors therefore removes the need to rotate the MS coil arrangement through 180 degrees which is awkward to do and may lead to inaccurate positioning of the MS coil arrangement relative to a patient’s head. Referring to Figure 3, four different adaptors 16a-d are presented allowing the same double coil winding to operate in four different modes without any modification to the winding coil itself or the housing structure. Figures 3a and c show adaptors 16 enabling operation of the system to provide a stimulation to a patient, and Figures 3b and d provide adaptors that provide a sham or placebo effect to a patient. The first and second coil windings 4,6 are provided in a side-by-side configuration. This configuration as demonstrated in Figure 4a causes the magnetic field produced by the two windings to combine at least partially to produce a greater magnetic field in the zone between and underneath the windings and thus in operation toward a patient. Viewed from above the first and second windings 4,6 may be termed left 4 and right 6 hand coil windings for clarity purposes. Intermediate the stimulator 3 and the windings 4,6 is an adaptor 16. Arrows again indicate the current flow directions in the four different embodiments. Each of the adaptors 16a-d presented in Figures 3a-d connect to the stimulator in the same way as the adaptors presented in Figure 2, however in these embodiments there are four connections to the two windings required. Referring to Figure 3a, enhanced stimulation in a target zone is enabled through the provision of adaptor 16a and the current flow pathways enabled by this adaptor. The current flow around the windings must be generally aligned at a location intermediate the two windings 4,6. This can be seen in Figure 3a where the current flow around the first and second windings 4,6 is in opposite directions (clockwise and anticlockwise) respectively. The adaptor 16a defines a current pathway from the first terminal 28 from the stimulator 3 to a second terminal 20 connected to the first winding 4, a third terminal 22 from the first winding to a fourth terminal 32 to the second winding 6 and a fifth terminal 34 from the second winding 6 to a sixth terminal 29 to a stimulator. Referring to Figure 3b, the adaptor 16b is designed to provide current flow pathways therethrough showing the terminals using the same reference numerals as used in Figure 3a that means the magnetic fields generated by each of the first and second windings 4,6 are at least partially cancelled meaning the coil can be used in a sham or placebo mode of operation. In this embodiment the current flow direction around the windings is the same (i.e. in this embodiment both are clockwise) meaning in the zone intermediate the two windings 4,6 the magnetic fields are cancelled to a degree that there is no treatment to a patient, rather they feel scalp stimulation in the same way as is achieved through a normal treatment which would be achieved using the embodiments of Figures 3a and c. This effect is demonstrated by Figure 4b. Referring to Figure 3c this MS coil system can be compared to the MS coil system of Figure 3a as also providing a treatment or combined magnetic field when current is supplied through the windings simultaneously. The current pathways are presented showing the terminals using the same reference numerals as used in Figure 3a. This is different to that of Figure 3a however as the current flow through the left-hand winding 4 is the opposite direction to that of the same right-hand coil winding 6 of Figure 3a, and the current flow direction through the right-hand coil 6 winding of Figure 3c is the opposite to that of the same right-hand coil winding 6 of Figure 3a. The different effect achieved can again be described with respect to Figure 6 and allows switching between posterior to anterior (PA) and anterior to posterior (AP) pulse waveforms. Referring to Figure 3d, the MS coil system can be compared to the embodiment of Figure 3b, where in this embodiment again the current flow directions are opposite to one another (anticlockwise for the left-hand winding and clockwise for the right-hand winding) meaning that the generated magnetic fields at least partially cancel each other. Again the current pathways are presented showing the terminals using the same reference numerals as used in Figure 3 a. Figure 4a and 4b display the computational modelling of two operable modes, corresponding to Figure 3a and Figure 3b, respectively. In the first mode, the E-field profile resembles that of conventional ‘figure-of-eight’ coils. However, in the second mode (Figure 4b), it is evident that the E-fields of the two windings 4 and 6 attenuate each other in the central region, resulting in minimal stimulation. Conversely, in areas below the windings 4 and 6, an induced field is visible. The head model 40 was assumed to consist of homogeneous tissue. Referring to Figure 5 a schematic representation is made of a MS coil as described with respect to any of the Figures and for illustrative purposes only presents a double coil winding. The windings 4,6 are incorporated into a cap 42 to be worn by the test subject. The coil windings may be moveable relative to the cap between multiple operable configurations to allow treatment at multiple locations without reorientation of the cap 42 itself. Presented in Figure 6(a) is an illustration of the placement and orientation of a TMS system, highlighting the key distinctions between PA-TMS (posterior-to-anterior) and AP-TMS (anterior-to-posterior) when applied to the brain using the conventional method, involving a 180-degree coil rotation. Figure 6b illustrates the current in the windings, showcasing monophasic PA and AP pulse waveforms. These waveforms, as shown in Figure 6(c), can activate distinct sets of neurons. The adaptors 16 are also capable of facilitating waveform changes for various pulse shapes, including monophasic, biphasic, polyphasic, rectangular, or PWM pulses. Although particular embodiments of this disclosure have been described, it will be appreciated that many modifications / additions and / or substitutions may be made within the scope of the claims.

Claims

1. A Magnetic Stimulation (MS) coil system for connection to a current pulse generator, the MS coil system comprising:- At least one coil winding for delivering a magnetic field to a target zone of a body;a first and second adaptor for providing a current pathway from the stimulator to the at least one coil winding for delivering current pulses to the at least one coil winding, the first and second adaptors being releasably engageable between a stimulator and the at least one coil winding independently of one another;wherein the first adaptor is arranged to enable current flow in a first direction around the coil winding, and the second adaptor is arranged to enable current flow in a second opposite direction around the coil winding.

2. A MS coil system according to claim 1 comprising a first and second coil winding each independently releasably engageable with the first or second adaptor.

3. A MS coil arrangement according to claim 2 wherein the first and second windings are in a side-by-side configuration.

4. A MS coil system according to any preceding claim wherein the first direction is a clockwise direction around the first winding, and the second opposite direction is an anticlockwise direction around the second winding.

5. A MS coil system according to any of claims 2-4 wherein the first adaptor is arranged to engage with the first winding such that the current flow direction in the first winding is in the first direction, and the first adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is in a second opposite direction.

6. A MS coil system according to claim 5 wherein the second adaptor is arranged to engage with the first winding such that the current flow direction in the first winding is in the first direction, and the second adaptor is arranged to engage with the secondwinding such that the current flow direction in the second winding is also in the first direction.

7. A MS coil system according to claim 5 wherein the first direction is clockwise and the second direction is anticlockwise, wherein the second adaptor is arranged to engage with the first winding such that the current flow direction in the first winding is in the anticlockwise direction, and the third adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is in the clockwise direction.

8. An MS coil system according to claim 6 wherein the first direction is clockwise and the second direction is anticlockwise, wherein the MS coil arrangement further comprises a third adaptor arranged to engage with the first winding such that the current flow direction in the first winding is in the anticlockwise direction, and the third adaptor is arranged to engage with the second winding such that the current flow direction in the second winding is in the clockwise direction.

9. A MS coil system according to any of claims 2-8 wherein the first and second adaptor each define a current pathway from:- a first terminal from a stimulator to a second terminal connected to the first winding;a third terminal from the first winding to a fourth terminal to the second winding;a fifth terminal from the second winding to a sixth terminal to a stimulator.

10. A MS coil system according to claim 9 wherein the second, third, fourth and fifth terminal of the first and second adaptors comprise sockets.

11. A MS coil system according to any preceding claim further comprising a stimulator for emitting current pulses to the at least one winding.

12. A MS coil system according to any preceding claim comprising a Transcranial Magnetic Stimulation (TMS) system.13

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