GB2567872A

GB2567872A - Magnetic stimulation coil arrangement

Info

Publication number: GB2567872A
Application number: GB1717716.3A
Authority: GB
Inventors: Biginton Matthew
Original assignee: Magstim Co Ltd
Current assignee: Magstim Co Ltd
Priority date: 2017-10-27
Filing date: 2017-10-27
Publication date: 2019-05-01
Anticipated expiration: 2037-10-27
Also published as: GB201717716D0; GB2567872B

Abstract

A Magnetic Stimulation (MS) coil arrangement for use in apparatus for the magnetic stimulation of tissue. The MS coil arrangement comprises a stacked structure of: at least one coil winding 4a,4b formed from an elongate conductive element; first 6 and second 8 winding retaining structures which are preferably rigid metallic plates positioned respectively above and below the at least one coil winding 4a,4b; a first damper 10 provided intermediate the first winding retaining structure 6 and the at least one winding 4a,4b and a second damper 12 provided intermediate the second winding retaining structure 8 and the at least one winding 4a,4b; a securing arrangement 22, 24, 26 for securing the first 6 and second 8 winding retaining structures relative to one another. The arrangement may also comprise a housing and the winding retaining structures will preferably have a thickness of 5mm and comprise alloys of stainless steel or titanium. The dampers will preferably be elastically deformable and there may be a ferromagnetic composite material provided intermediate the first winding retaining structure and the windings. The arrangement may comprise a plurality of stacked windings, wherein each winding has a damper there between.

Description

(57) A Magnetic Stimulation (MS) coil arrangement for use in apparatus for the magnetic stimulation of tissue. The MS coil arrangement comprises a stacked structure of: at least one coil winding 4a,4b formed from an elongate conductive element; first 6 and second 8 winding retaining structures which are preferably rigid metallic plates positioned respectively above and below the at least one coil winding 4a,4b; a first damper 10 provided intermediate the first winding retaining structure 6 and the at least one winding 4a,4b and a second damper 12 provided intermediate the second winding retaining structure 8 and the at least one winding 4a,4b; a securing arrangement 22, 24, 26 for securing the first 6 and second 8 winding retaining structures relative to one another. The arrangement may also comprise a housing and the winding retaining structures will preferably have a thickness of 5mm and comprise alloys of stainless steel or titanium. The dampers will preferably be elastically deformable and there may be a ferromagnetic composite material provided intermediate the first winding retaining structure and the windings. The arrangement may comprise a plurality of stacked windings, wherein each winding has a damper there between.

FIG. 3

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIG. 2

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FIG. 3

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FIG. 5

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FIG. 6A

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FIG. 7B

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FIG. 8

-1Magnetic Stimulation Coil Arrangement

The present invention relates to a Magnetic Stimulation (MS) and preferably a Transcranial Magnetic Stimulation (TMS) coil arrangement whereby the object of the invention is to minimise the acoustic noise and/or movement of one or more coil windings due to the magnetic field generated in the turns of the winding(s).

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 stimulation 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 Transcranial Magnetic Stimulation (TMS) winding. An intense sinusoidal magnetic field is formed near the winding and is used to stimulate neurons in patients for medical and research applications. An example of a coil arrangement is presented in Figure 1 which shows a single winding coil arrangement 2 presented without a covering that may suitably be positioned on a patient’s cranium. The winding is made up of a single wound conductive element connected to the capacitor via an elongate neck allowing manipulation of the coil arrangement to the appropriate location.

Such TMS coil arrangements are used for medical and research applications. In operation however, TMS coil arrangements make both a distinctive sound and also vibrate caused by rapid deformation of the turns in each winding. This results from attraction of adjacent turns in the winding, where the resultant force from the magnetic fields from adjacent turns means that there is radial vibration as the high current passes through the turns.

-2This noise is significant, and can result in both a sound audible to the patient and feeling through the housing of the coil arrangement. This can in some circumstances cause unwanted side effects such as headaches.

The present invention addresses these deficiencies.

According to an aspect of the present invention there is a Magnetic Stimulation (MS) coil arrangement for use in apparatus for the magnetic stimulation of tissue, the MS coil arrangement comprising a stacked structure of:

at least one coil winding formed from an elongate conductive element;

first and second winding retaining structures positioned respectively above and below the at least one coil winding;

a first damper provided intermediate the first winding retaining structure and the at least one winding and a second damper provided intermediate the second winding retaining structure and the at least one winding;

a securing arrangement for securing the first and second winding retaining structures relative to one another.

The securing arrangement, first and second winding retaining structures and first and second dampers are configured such that in operation there is substantially no audible output from the MS coil arrangement or relative movement between the first and second winding retaining structures. The first and second retaining structures together with the first and second dampers have the effect of dampening movement of the adjacent turns of the at least one winding and also reducing acoustic and vibration output.

The MS coil arrangement preferably further comprises a housing for housing the stacked structure.

The first and second winding retaining structures are preferably substantially rigid. This means that there is substantially no deflection or bending during normal use.

-3The first and second winding retaining structures preferably comprise first and second plates.

The first and second plates are beneficially thermally conductive to allow heat transfer away from the one or more windings. The first and/or second plates are preferably metallic plates. The first and/or second plates are beneficially metallic and beneficially comprise a metal of relatively low electrical conductivity. Low relative electrical conductivity is beneficial to minimise the generation of Eddy currents in the first and/or second plates during operation thus reducing heat generated in the plates. As an example alloys of stainless steel or titanium may be utilised. The first and/or second plates may alternatively comprise carbon fibre composite material.

The first and/or second plates preferably have a thickness of between 2-10mm, and more preferably in the range of 4-6mm and even more preferably substantially 5mm. This has been determined to give appropriate rigidity.

The first winding retaining structure is positioned above the coil winding and the MS coil arrangement has a non-patient facing side above the first winding retaining structure, and the first winding retaining structure is beneficially formed of a ferromagnetic material. This has the effect of distorting a magnetic field produced by the one or more coil windings such that it is now asymmetric about the plane of the winding(s). The reluctance of the material on the non-patient facing side of the coil is now significantly lower and as a result most of the energy delivered to the winding(s) is now stored in the volume on the patient facing side of the coil. This means that for the same applied energy the magnetic field strength is higher on the patient facing side of the MS coil arrangement (in the patient’s tissue). Alternatively, the same magnetic field strength may be supplied to the patient whilst using less energy in comparison to not using ferromagnetic material. This means that not only less energy is used to drive the MS coil arrangement but less joule heating occurs in the winding(s) and can increase the amount of stimulations the coil can perform before overheating.

The first winding retaining structure preferably comprises a ferromagnetic plate having a separation gap in the plate that mirrors at least part way between the radially inner and radially outermost turn of the or each of the winding(s). This is beneficial as a solid

-4ferromagnetic (metal) plate for example generates significant Eddy currents and quickly heats up. This significantly limits the number of pulses of current that may be supplied through the coil before the plate becomes too hot. The provision of such a separation gap minimises this effect by preventing significant Eddy current generation.

A ferromagnetic composite may be provided intermediate the first winding retaining structure and the winding(s). Such a ferromagnetic may be termed a Soft Magnetic Composites (SMC). Ferromagnetic composites are typically pressed and thermally-treated powder metal composed of encapsulated iron powder particles that are compacted to form the desired shape. A typical ferromagnetic composite is Somaloy. This ferromagnetic composite acts as an improved magnetic mirror as is more resistive to saturation than a solid plate.

The first and preferably second damper are beneficially capable of allowing some movement of the winding(s) and also act as an acoustic absorber. The first and preferably second dampers are preferably elastically deformable or are capable of flowing to accommodate the winding movement and acoustic noise generated. The dampers may be made of a material having a plurality of interstices therein such as a foam, or a gel like material. The dampers are beneficially thermally conductive to enable heat transfer away from the winding(s).

The securing arrangement may comprise a fixing element extending between the first and second winding retaining structure for securing the first and second winding retaining structures relative to each other. The fixing element may comprise a bolt. The fixing element may further communicate with the first and/or second damper to enable securing of the first and/or second damper. A fixing element in the form of a bolt may extend between the first and second winding retaining structures and the first and/or second dampers.

At least one of the first and/or second winding retaining structures may be configured to restrict radial movement of the one or more winding retaining structures. At least one of the first and second winding structures extends around the peripheral edge of the one or more windings. The first and second winding structures preferably cooperate with one another.

-5The MS coil arrangement may comprise a plurality of stacked windings, wherein each winding has a damper therebetween.

It will be appreciated that the dampers and/or the winding retaining structures are preferably shaped to mirror an area at least above and below the area occupied by the turns of the winding(s). The dampers and/or the winding retaining structures may be shaped to generally match the shape of the winding(s).

The present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of an MS coil arrangement as known in the art.

Figure 2 is a schematic side view of a double winding MS coil arrangement according to an illustrative embodiment of the present invention.

Figure 3 is a schematic exploded representation of an MS coil arrangement according to an illustrative embodiment of the present invention.

Figure 4a is a schematic exploded representation of an MS coil arrangement having multiple stacked individual windings (each made up of a double winding), and Figure 4b is the same MS coil arrangement in non-exploded representation.

Figure 5a is a schematic exploded representation of an MS coil arrangement having multiple stacked individual and single windings, and Figure 5b is the same MS coil arrangement in non-exploded representation.

Figure 6 is a further illustrative embodiment of the present invention.

Figure 7a and b are perspective views of two different illustrative retaining structures for inclusion in an illustrative embodiment of the present invention.

-6Figure 8 is a further illustrative embodiment of the present invention.

Referring to Figure 2 there is a schematic side representation of illustrative embodiment of the present invention. Schematically represented is a magnetic stimulation (MS) coil arrangement 2 comprising a stacked structure of a coil winding 4, first and second winding structures 6, 8 and intermediate the coil winding 4 and respective first and second winding retaining structures 6, 8 are first and second dampers 10, 12 respectively. A securing arrangement 14 is shown and the stacked structure as a whole is housed within a housing

16. It will be appreciated that the MS coil arrangement 2 has a patient facing side or lower side 18 that is brought towards a patient in use and an opposing upper or operator facing side 20 which generally faces away from the patient in operation. The structure of the MS coil arrangement 2 is stacked or layered such that each respective layer is on top of another layer.

As presented in Figure 2 the coil winding 4 is viewed from the side. The coil winding 4 itself comprises one or more windings where each winding is made up of a plurality of radially wound turns. The one or more windings can be formed of a single elongate conductive element. In alternative embodiments as will be described further below, the one or more coil winding(s) 4 may comprise multiple independent windings provided in the stacked structure that themselves each may comprise one or more adjacent windings formed of a single elongate conductive element.

Referring now to Figure 3 presented is an illustrative embodiment of the present invention in exploded perspective view. The stacked structure of the MS coil arrangement is presented and the coil winding 4 is shown as a single elongate conductive element wound into first and second windings 4a, 4b disposed adjacent to one another. The turns of each of the windings 4a, 4b are wound radially. In this embodiment each of the windings 4a, 4b are in the same plane.

The first and second winding retaining structures 6, 8 are provided above and below the windings 4a, 4b and the first and second dampers 10, 12 are provided intermediate the windings 4a, 4b and the respective first and second winding retaining structures 6, 8. A

-7simple securing arrangement 14 is shown comprising a bolt 22 extending through apertures 24 in the first and second winding retaining structures 6, 8 and first and second dampers 10, 12 to be held by nut 26. It will be appreciated that multiple apertures 24 may be provided for multiple securing arrangements whereby the apertures 24 are provided in portions of the first and second winding retaining structures 6, 8 and first and second dampers 10, 12 that project beyond the peripheral edges of the windings 4a, 4b. This ensures that the securing together of the stacked structure does not impact upon the functioning of the first and second windings 4a, 4b. It will be appreciated, that in some embodiments, the damper material may be a flowable material such as a gel and in such a configuration it may be unnecessary to provide any fixing mechanism for the damper rather the damper is simply seated between the windings 4a, 4b and the first or second winding retaining structures 6, 8.

In combination the provision of the rigid first and second winding retaining structures and dampers 10, 12 prevent movement or vibration of the MS coil arrangement as a whole due to the rigidity of the first and second winding retaining structures. The dampers allow localised movement of the winding 4 and act as an acoustic absorber. This means that the MS coil arrangement as a whole does not vibrate and only a low volume audible sound is emitted during operation.

The first and second winding structures 6, 8 are preferably both provided in the form of plates. The plates are beneficially formed to substantially cover both above and below the turns of the windings 4a, 4b. The plates are rigid meaning that there is no deflection or bending during normal use. The plates are preferably metallic however are made from a material that has a relatively low electrical conductivity to minimise the generation of eddy currents. Alternative materials for the plates are envisaged such as, for example, carbon fibre. A separation gap 28 is provided in the plates which acts to minimise Eddy currents generated in use. A problem with the generation of Eddy currents is heating of the plates and it is preferable accordingly that these are minimised. By providing a separation gap in a portion of the plate that overlaps the turns of each of the windings the generation of Eddy currents can be minimised. It will be appreciated that for each winding 4a, 4b a separation gap 28 should be present extending to overlap from a radially inner to a radially outer most

-8portion of the turns of the winding. This is even though the plate 6, 8 is beneficially a single plate substantially covering multiple windings 4a, 4b.

The first and preferably second plates require a thickness to minimise vibration and have sufficient rigidity and a typical thickness is around 5mm depending on the exact material utilised.

The first winding retaining structure/plate 6 positioned above the winding toward the operating facing side of the MS coil arrangement may comprise a ferromagnetic material. As described above this means that less energy may be used to drive the MS coil arrangement and less joule heating occurs in the winding(s) thereby increasing the amount of stimulations the coil can perform before overheating. In addition, the thickness of the first and second winding retaining structures can be minimised.

The first and second dampers 10, 12 have been presented as plates however may take various forms such as a foam, gel or other material capable of deforming and/or absorbing acoustic output from the winding 4. Thus, the dampers are beneficially deformable. The dampers are also beneficially capable of extracting heat from the windings, thus are beneficially thermally conductive.

Referring now to Figures 4a and b a further embodiment of the present invention is presented comprising multiple individual coil windings. In such an embodiment multiple windings are each separated by a damping layer and retained between first and second winding retaining structures accordingly. As can be seen in Figure 4b, a layer structure is then provided having aligned apertures 24 through which a bolt 22 can be transferred thereby clamping the first and second winding retaining structures having the multiple layers therebetween.

Referring now to Figure 5, the first and second winding retaining structures are configured to resist radial movement of the one or more winding retaining structures themselves. This is caused as a result of radial movement of the turns of the winding. Resistance may be achieved by the provision of overlapping peripheral edge portions 30 that overlap upon

-9tightening of the securing arrangements. It is further noted that in the embodiment of Figure 5 the separation gap is shown as a continual gap across portions of both the first and second windings 4a, 4b. It will be appreciated that the same effect of minimising Eddy currents is achieved.

Referring to Figure 6a and b, a further embodiment is presented comprising multiple single windings 4. The effect of providing stacked windings in such a configuration is to enable current sharing and reduce overall loses in the coil arrangement. Again, the first winding retaining structure 6 may be a ferromagnetic material.

Referring to Figure 7a and b, two alternative winding retaining structures are presented showing the alternative configuration of the separation gap designed to mirror and overlap the distance between the radially inner and radially outer most turn of each of the windings to prevent a build-up of Eddy currents.

Referring to Figure 8 there is a schematic exploded perspective representation of an illustrative embodiment of the present invention. In this embodiment there is a ferromagnetic composite plate 36 provided intermediate the first winding retaining structure and the winding(s). The ferromagnetic composite may be Somaloy. This ferromagnetic composite acts as an improved magnetic mirror as is more resistive to saturation that a solid plate. The ferromagnetic composite is preferably provided intermediate the first plate 6 and a damper 10, where a further damper 10 is positioned between the ferromagnetic composite plate 36 and the first plate 6. The ferromagnetic composite plate 36 may extend into the volume 38 defined by the radially innermost turn of each or the winding. Thus the ferromagnetic composite plate 36 may further extend through the damper 10 intermediate the plate 36 and the winding(s).

Aspects of the present invention have been described by way of example only and it will be appreciated by the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims. It is also noted that MS coils come in a vast variety of shapes, sizes and general topologies that the basic principles in this patent can be applied.

Claims

1. A Magnetic Stimulation (MS) coil arrangement for use in apparatus for the magnetic stimulation of tissue, the MS coil arrangement comprising a stacked structure of:

at least one coil winding formed from an elongate conductive element;

2. A MS coil arrangement according to claim 1 comprising a housing for housing the stacked structure.

3. A MS coil arrangement according to any preceding claim wherein the first and second winding structures are rigid.

4. A MS coil arrangement according to any preceding claim wherein the first and second winding structures comprise first and second plates respectively.

5. A MS coil arrangement according to claim 4 wherein the first and/or second plates are metallic plates.

6. A MS coil arrangement according to any of claims 4-5 wherein the first and/or second plates are metallic plates comprising alloys of stainless steel or titanium.

7. A MS coil arrangement according to any of claims 4-6 wherein the first and/or second plates have a thickness of between 2-10mm and more preferably in the range of 4-6mm and even more preferably substantially 5mm.

8. A MS coil arrangement according to any preceding claim wherein the first winding retaining structure is positioned above the coil winding and the MS coil arrangement has a non-patient facing side above the first winding retaining structure, and the first winding retaining structure is formed of a ferromagnetic material.

9. A MS coil arrangement according to 8 wherein the first winding retaining structure comprises a ferromagnetic plate having a separation gap in the plate that overlaps at least part way between the radially inner and radially outer most turn of the or each of the winding(s).

10. A MS coil arrangement according to any preceding claim wherein the first and/or second dampers are elastically deformable or are capable of flowing to accommodate movement of the winding in operation and acoustic noise generated thereby.

11. A MS coil arrangement according to any preceding claim wherein the securing arrangement comprises a fixing element extending between the first and second winding retaining structure for securing the first and second winding retaining structure relative to each other.

12. A MS coil arrangement according to any preceding claim wherein at least one of the first and/or second winding retaining structures is configured to restrict radial movement of the one or more winding retaining structures.

13. A MS coil arrangement according to any preceding claim comprising a plurality of stacked windings, wherein each winding has a damper therebetween.

14. A MS coil arrangement according to any preceding claim further comprising a ferromagnetic composite material provided intermediate the first winding retaining structure and the winding(s).

15. A MS coil arrangement according to claim 14 wherein the ferromagnetic composite material extends into a volume defined by the radially innermost turn of one or more winding(s).

16. A MS coil arrangement as defined in any preceding claim whereby the or each winding is non-planar.