GB2576678A

GB2576678A - Magnetic stimulation coil arrangement

Info

Publication number: GB2576678A
Application number: GB1918170.0A
Authority: GB
Inventors: Biginton Matthew; Clamp Andrew
Original assignee: Magstim Co Ltd
Current assignee: Magstim Co Ltd
Priority date: 2016-06-08
Filing date: 2017-06-07
Publication date: 2020-02-26
Anticipated expiration: 2037-06-07
Also published as: GB2576678B; GB2565003A; WO2017212253A1; GB201818212D0; GB201609981D0; GB2565003B; GB201918170D0

Abstract

A magnetic stimulation coil arrangement for use in stimulation of the brain using Transcranial Magnetic Stimulation (TMS) has one or more wire coil windings 6 in a housing 20. One or more inlets 14, each preferably at the core 10 of a winding, feed a coolant flow pathway 18 which extends above and/or below the windings and is formed by one or more walls extending across a gap between the windings and the housing. The coolant flow pathway extends in more than one direction, and radially outwards from the inlet; it may be spiral shaped. It converges to an outlet 26 which may be in the centre of the housing. The windings may be embedded in a potting material inside a polymeric casing, both having a thermal conductivity of greater than 1 W/mK. The coolant may be an oil or water.

Description

Magnetic Stimulation Coil Arrangement

The present invention relates to a magnetic stimulation coil arrangement for use in apparatus for magnetic stimulation of tissue, particularly for use in stimulation of the brain using Transcranial Magnetic Stimulation (TMS).

A magnetic stimulation apparatus comprises a pulse generator electrically connected to a coil arrangement. The coil arrangement comprises one or more windings (typically two) each comprising a wound elongate conductive element having a plurality of spaced apart turns. It will be appreciated that the elongate conductive element could be multi-strand wire, litz wire and/or comprise a plurality of stacked windings. The pulse generator is arranged to supply a pulse of high current through the elongate conductive element which has the effect of generating an electromagnetic pulse adjacent the windings which in turn induces relatively small electric currents in the tissue to be treated.

A problem exists in that passing a high current through the elongate conductive element causes a significant amount of heat to be generated by joule heating. This heat transfers from the windings through the surrounding media and to the patient surface of the coil. The temperature of the patient surface ideally should be kept below 41 °C. If the patient surface exceeds 41 °C for long enough there is the potential localised heating of the patient’s tissue.

Accordingly a cooling system is provided which typically includes a fluid flowing adjacent to but electrically insulated from the windings. Coolant fluid is passed adjacent the windings during operation transferring heat generated by the current flowing through the windings during operation away from the windings.

Whilst known cooling systems take heat away from the windings, it is desirable to operate the magnetic stimulation coil apparatus at higher power protocols with reduced time delay between pulses. This has the effect that more heat must be transferred away from the windings in order to avoid the patient surface exceeding 41 °C.

-2An improved arrangement has been devised.

A magnetic stimulation coil arrangement for use in apparatus for the magnetic stimulation of tissue, the magnetic stimulation coil arrangement comprising one or more coil windings formed from an elongate conductive element, the one or more coil windings each wound to comprise a plurality of turns, and a housing for housing the one or more windings, wherein the magnetic stimulation coil arrangement further comprises a coolant flow pathway above and/or below the winding(s) and intermediate the winding and the housing and being formed by one or more walls extending at least part way across a gap defined between the winding and the housing, the wall(s) forming a cooling channel that defines the coolant flow pathway, where the coolant flow pathway extends in more than one direction .

The present invention enables much improved cooling of a magnetic stimulation coil arrangement. This enables the arrangement to be operated with less downtime between pulses being administered to a patient as the heat transfers away from the winding(s) and the delay of heat transfer to the patient surface is improved.

The coolant flow pathway is intermediate the winding(s) and the housing and preferably arranged such that the winding(s) are external of the cooling channel.

The winding(s) are preferably axially wound, and the winding(s) and cooling channel are preferably axially spaced.

The one or more windings are individually substantially planar.

It will be appreciated the cooling fluid may comprise different forms such as water or oil and possibly air.

The coolant flow pathway may extend in a spiral configuration having a plurality of cooling channel turns.

The cooling channel turns preferably wind radially in the spiral configuration.

-3The cooling channel turns are preferably in the same plane. The cooling channel turns are preferably in the same plane as the turns of a corresponding coil winding

The cooling channel turns are preferably defined by a wall extending at least part way across a gap between the winding and the housing.

The winding has a patient facing side and an opposing upper side, and the cooling channel may be provided to the patient facing side. It is important to ensure that the cooling effect is maximised adjacent the patient facing side. It will be appreciated however that for extra cooling capability a coolant flow pathway as described herein may be provided at the nonpatient facing or upper side.

It is preferable that the turns of the winding are positioned in a side by side configuration with the cooling channel therebetween. The separation of the cooling channel in a radial direction is preferably constant. The separation of the cooling channel in the axial direction may be variable to accommodate the desired outer surface contours of the housing.

The turns of the cooling channel are preferably positioned in a side by side configuration with the cooling channel therebetween.

The turns of the cooling channel may extend outwardly from a radially inner inlet to a radially outer outlet.

In the case of a double winding the coolant channel may turn in an anticlockwise direction from its inlet to the outlet on one winding and in a clockwise direction from inlet to outlet on the other winding.

The outlet of the spiral channel may be arranged to direct coolant flowing therefrom in a direction as a continuum of the spiral configuration. This means the wall defining the

-4channel extending across the gap between the winding and the housing may terminate without changing direction.

The magnetic stimulation coil arrangement preferably comprises an inlet formation for directing coolant into the channel, the inlet formation comprising at least one inlet port configured to direct coolant radially outwardly. The radial direction is a direction substantially transverse to the axial direction of the turns of the winding. The flow direction of the coolant is beneficially transferred from axial to radial by the inlet formation.

The inlet formation may comprise multiple spaced apart inlet ports to the channel. The inlet formation is preferably provided radially inwardly of the turns of the winding. The inlet ports are preferably regularly spaced apart. In one embodiment there are three inlet ports.

The multiple inlet ports preferably direct coolant into the first cooling channel turn. Each inlet port preferably directs coolant fluid radially outwardly.

The magnetic stimulation coil arrangement preferably comprises a first and a second winding, and wherein the cooling channel is provided in a first spiral configuration adjacent to the first winding and a second cooling channel adjacent to the second winding. Transcranial Magnetic Stimulation (TMS) coil arrangements typically comprises a first and second winding. It is beneficial that a separate coolant flow pathway having a spiral cooling channel is associated with each winding. As such it is beneficial an inlet formation is associated with each winding. There are beneficially separate coolant inlet flow paths. It is beneficial for compactness of the coil arrangement that each spiral cooling channel share the same flow path out of the coil arrangement.

The one or more windings preferably have a patient facing side and an upper side, where the coolant flow pathway extends between the peripheral edge of the one or more windings and the housing. Thus, coolant flows from the spiral channel and may flow around the peripheral edge, typically then dispersing around the peripheral edge and around the operator side of the one or more windings.

-5The spiral configuration of the cooling channel preferably terminates before the portion of the coolant flow pathway between the peripheral edge of the one or more windings and the housing.

The one or more windings are preferably provided with a potting material to encapsulate the turns of the winding. This is to prevent coolant contacting the elongate conductive forming the winding(s). This is particularly important in the case of water being used as the cooling fluid.

A polymeric layer (casing) may be arranged to cover the potting material. The thermal conductivity of the polymeric layer is beneficially greater than 0.5 W/mK, and preferably greater than 1 W/mK. This allows improved sealing of the potting material in case of failure cracks forming in the potting material and coolant reaching the elongate conductive element. It also allows for ease of potting the elongate conductive element. It further allows good thermal transfer away from the elongate conductive element. The walls defining the cooling channel may further be formed integrally with or adhered to the polymeric layer with thermally conductive heat sink compound for example. The use of a polymeric layer allows easier formation of the inlet formations and channels through injection moulding or vacuum casting techniques.

In an embodiment of the invention the coolant flow pathway is defined directly between the potting material and the housing. This further improves thermal conductivity away from the elongate conductive element.

The one or more coil windings may comprise a patient facing side and a non-patent facing side, and the coolant flow pathway may extend between the housing and one or more coil windings on both the patient and non-patient facing sides, and wherein a first spiral configuration is provided on the patient facing side and a second spiral configuration is provided on the non-patient facing side.

According to a second aspect of the present invention there is a magnetic stimulation coil arrangement for use in apparatus for the magnetic stimulation of tissue, the magnetic stimulation coil arrangement comprising one or more coil windings formed from an elongate conductive element, the one or more coil windings each wound to comprise a

-6plurality of radially wound turns, and a housing for housing the one or more windings, wherein the magnetic stimulation coil arrangement comprises an inlet formation open to a coolant flow pathway intermediate the winding and the housing, the inlet formation having at least one inlet port for directing the coolant flow radially outwardly.

The inlet formation may have multiple spaced apart inlet ports to the channel. The multiple inlet ports are beneficially regularly spaced apart and beneficially point away from the outlet of the coil arrangement.

The one or more windings preferably have a patient facing side and an upper side, where the coolant flow pathway extends between the peripheral edge of the one or more windings and the housing.

Increased cooling efficiency may be achieved by having inlet ports both on the patient side and operator side of the coil between the windings and housing.

The one or more windings are preferably provided in a potting material. The potting material preferably has a thermal conductivity greater than 0.5 W/mK and preferably greater than 1 W/mK. The potting material may be epoxy based and/or rubber based. The potting material may also include metallic fillers and/or ceramic fillers. It would be obvious that ferromagnetic fillers, particles or components or elongates could be introduced into the potting material to enhance the magnetic field at the patient facing side of the coil arrangement as described in GB2360213 and the patent family including US8246529.

A polymeric layer is preferably arranged to cover the potting material. The thermal conductivity of the polymeric layer is preferably greater than 0.5 W/mK and preferably greater than 1 W/mK.

The coolant flow pathway may alternatively be defined directly between the potting material and the housing.

Aspects of the present invention will now be described by way of example only with reference to the accompanying Figures where:

-7Figure 1 is a schematic cross sectional representation of a double winding magnetic stimulation coil arrangement according to an exemplary embodiment of the present invention.

Figures 2a-d are schematic representations of half of the double winding magnetic stimulation coil arrangement presented in Figure 1, where Figure 2a is the housing, Figure 2b is a casing for encapsulating the potting material of Figure 2c and within the potting material is the elongate conductive element wound to form the winding as presented in Figure 2d (represented as a doughnut for simplicity), all from an upper or non-patient perspective.

Figure 3a-d are perspective views as Figures 2a-d from an underside or patient-facing side according to an exemplary embodiment.

Figure 4a is a schematic perspective view of the underside of a housing of half a magnetic stimulation coil arrangement as presented in Figure 1, and Figure 4b is a schematic presentation of a magnetic stimulation coil arrangement as presented in Figure 4a with the housing removed for clarity.

Figure 5 is a graphical representation of a comparison of the winding temperature using an electrically inert oil (Midel 7131) and water in two exemplary embodiments of the present invention. The first exemplary embodiment utilises three inlet ports to the coolant flow pathway intermediate the winding and the housing in comparison to the temperature associated with the utilisation of a spiral configuration for the cooling channel.

Figure 6 is a representation of the coolant fluid flow in an embodiment of the invention utilising three inlet ports to the coolant flow pathway from above the windings as presented in Figure 6a, from beneath the windings as presented in Figure 6b, and from underside perspective and top perspective views as presented in Figures 6c and 6d respectively. It is noted that the housing has been removed for clarity purposes and it is the coolant flow itself that is modelled.

-8Figures 7a and 7b are schematic upper perspective and lower perspective representations of the coolant flow rate in an exemplary embodiment of the present invention utilising a cooling channel provided in a spiral configuration where a lighter colour is represented by higher flow rate and a darker colour by a lower flow rate. Again, the housing has been removed for clarity purposes.

Figures 8a, b, c and d show the flow patterns of coolant for the same input flow rate as viewed from the patient side of half of a double winding for an inlet formation having three ports using water and oil (Midel 7131) as presented in Figures 8a and 8b respectively, and the same input flow rate for water and oil (Midel 7131) for a cooling channel having a spiral configuration as presented in Figures 8c and 8d, respectively. Figures 8 e, f, g and h show a steady state thermal map as viewed from the patient side of the winding for the same variants as presented in Figures 8a to 8d plotted on the interface between the cooling fluid and the casing (32) and Figure 8i, j, k and 1 show the steady state thermal map plotted on the outer housing as viewed from the patient side of the coil for the same embodiment.

Figure 9 is a graphical representation of the winding temperature utilising a three port inlets without the spiral channel which compares in plot lines a and b the effect of utilising a polymeric layer to house the potted windings utilising a plastic with a low and high thermal conductivity for water as the coolant. Plot lines c and d are the same comparison utilising oil.

Referring now to Figure 1 there is a schematic cross-sectional representation of an exemplary embodiment of the present invention. Figure 1 is a double winding coil arrangement typically utilised for TMS. The magnetic stimulation coil arrangement comprises a patient facing side (2) and non-patient facing side (4). A cross section through the windings (6) is presented meaning that the turns (8) of the winding (6) are wound radially outwardly leaving a radially inner space or core (10) at the centre of each of the windings (6). Provided within this core (10) is a chamber (12) for receipt of coolant fluid through the inlet (14) with the flow direction indicated by arrows (16). Coolant flows through the inlet (14) into the chamber (12) and into a coolant flow pathway (18) which is

-9provided intermediate the windings (6) and the housing (20). The coolant flow pathway (18) is axially spaced relative to each of the windings (6). It will be appreciated that the winding(s) are external of the coolant flow pathway (18). The coolant flow pathway (18) is schematically presented in Figure 1 by a cooling channel (22) provided in the form of a spiral configuration having a plurality of cooling channel turns (24). It will be appreciated, however, that the cooling channel (22) may take other forms. For example the channel may be defined by multiple turns whereby the channels extend across the cooling area adjacent the winding(s). The channels may comprise a linear portion. The channels may turn through substantially 180°. In a further aspect according to an aspect of the present invention the cooling channel (22) may be open without cooling channel turns therein (24).

Once the coolant that has been heated by the windings (6) has passed through the coolant flow pathway (18) it exits via the outlet (26). It will further be appreciated that as better presented with respect to Figure 3b an inlet formation is provided and as shown in Figure 1 comprises at least one inlet port (28).

As also represented in Figure 1 the coolant flow pathway has been presented adjacent the patient facing side (2) of the magnetic stimulation coil arrangement. It will also be appreciated that a further coolant flow pathway (18) may also be provided intermediate the housing (20) and winding (6) adjacent the non-patient facing side (4). This may increase the cooling effectiveness.

Referring now to Figure 2 presented are schematic perspective views of half of the magnetic stimulation coil arrangement as presented in Figure 1. Figure 2a presents the housing (20). Figure 2b presents the casing for the potted winding (6) where the potting is presented in Figure 2c and the winding in Figure 2d. It will be appreciated that the winding (6) is potted in the potting (30) which may in turn be housed in the casing (32) and wherein the coolant flow pathway (18) is provided intermediate the casing (32) and the housing (20).

Referring now to Figure 3 the patient facing side of half of a magnetic stimulation coil arrangement according to the exemplary embodiment is presented. Again in Figure 3a the

-10patient facing side (2) of the housing (20) is presented. This may be shaped to generally conform to a portion of a patient’s head or other body form. In Figure 3b a configuration of an exemplary inlet formation is presented. The inlet formation (34) may comprise an outwardly extending wall (36) that projects towards the inner surface of the housing (20). The wall (36) may be integrally formed with the casing (32). The wall (36) may extend to fit snuggly with the inner surface of the housing (20) or a separation gap may be provided. Alternatively the wall (36) may extend from the housing (20) towards the casing (32) or extend from both the casing (32) and the housing (20). The inlet formation may alternatively be an insert. The inlet formation (34) comprises one or more inlet ports (28) and in the exemplary embodiment three inlet ports (28) are presented. It will be appreciated that coolant flows into the chamber (12) axially relative to the winding (6) and then changes direction to be expelled through the inlet ports (28) radially outwardly. The radial outward direction is relative to the turns (8) of the winding (6). The inlet ports (28) are spaced apart and may be regularly spaced apart.

The winding (6) is potted to ensure there is no physical contact between the turns (8) of the winding (6) and the coolant. The potting material may comprise a variety of known materials such as resins. This may include PX439-N-GY or Durapot 801 for example which have thermal conductivities greater than 1 W/mK. The potting may have ceramic or metallic fillers and typically an epoxy resin is used however it is appreciated that a rubber based potting material could be utilised. It would be obvious that ferromagnetic fillers may also be added to enhance the field output from the coil.

The winding (6) may be potted with potting material heated into a form capable of flowing directly into the casing (32) during manufacture. It is important that the winding (6) does not come into physical communication with the coolant itself, particularly if the coolant is water.

It is further beneficial that the casing (32), forming a polymeric layer, is thermally conductive. It is beneficial that the thermal conductivity of the polymeric layer forming the casing (32) is greater than one. This has the benefit of ensuring high transfer of heat

-11from the winding (6) during operation to the coolant flowing between the housing (20) and casing (32).

In an aspect of the present invention it is envisaged that the potted winding can be provided in the housing (20) without the provision of the casing (32). In such an embodiment the coolant fluid would flow intermediate the potting (30) and the housing (20) without the provision of the casing (32). It is beneficial to utilise inert oil as the coolant in such an embodiment. It will be appreciated in such an embodiment the inlet formation (34) and /or spiral configuration is beneficially at least partially or fully provided by the potting (30).

Referring to Figure 4 there is a schematic perspective representation of an exemplary embodiment of the present invention where the housing (20) is presented in Figure 4a of a double winding that has been cut in half to represent a single winding within housing (20). Presented is the patient facing side (2). Referring to Figure 4b, the coolant flow pathway (18) is presented which is formed intermediate the winding (6) and the housing (20). The coolant flow pathway comprises a cooling channel (22) in a spiral configuration meaning that a plurality of cooling channel turns are defined. The inlet formation (34) is presented as being the same as that of Figure 3b and comprises three spaced apart inlet ports (28). Coolant fluid passes from the chamber (12) and then radially outwardly through the inlet port (28). The coolant flow hits the innermost cooling channel wall (40) and is forced to flow around the cooling channel turn and into the next cooling channel (22). The coolant flows around the cooling channel turns (24) until exiting through outlet (42). Outlet (42) is defined by a termination of the outermost cooling channel wall (44). The outlet (42) is presented such that the coolant flow is away from the outlet (26) and the coolant flowing from the outlet (42) can then pass around the peripheral edge of the casing (32) and around the non-patient side (4) of the cooling channel provided intermediate the housing (20) and winding (6).

Referring now to Figure 5, the effect of utilising a spiral cooling channel in comparison to an outlet formation (34) having three inlet ports (28) utilising water as a coolant is presented in graphical representation for the case of a casing with high thermal conductivity. It can be seen that the temperature of the winding utilising the spiral channel

-12(a) on comparison to the three port inlets (b) has an effect of reducing the winding temperature by approximately 7°C. As presented in plot lines (c) and (d) the effect of utilising a spiral channel with an oil coolant (as an example Midel 7131) in plot line (c) compared to a non-spiral configuration as shown in Figure 3b shows a marked difference where the plot line for the spiral channel is presented in (d). The provision of the spiral cooling channel has the effect of reducing the winding temperature when utilising oil by approximately 30°C.

Referring now to Figure 6 the flow pattern of an embodiment according to an aspect of the present invention is presented whereby the cooling channel is not provided in a spiral configuration but comprises three inlet ports for directing coolant flow in the radially outwardly direction. The coolant flows through inlets (14) into the chambers (12). The coolant flows from the chambers (12) through the inlet ports (28) and flows outwardly as coolant jets (48). These jets (48) flow predominantly radially outwardly from the inlet ports (28) and hit the peripheral edge of the internal surface of the housing (20). It can be seen that two of the jets contact the housing (20) whereas jets (48) intersect at zone (50). This is presented in Figure 6b. Subsequently, some of the coolant flows around the peripheral edge (46) and around the non-patient side (4) to the outlet (26) and some of the coolant as shown at reference numeral (52) flows to the outlet (26) on the patient facing side (2). The jets (48) that hit the inner surface of the housing at the peripheral edge then flow around the peripheral edge and over the non-patient facing side (4) back to the outlet (26). A sealed aperture (54) is provided where the winding elongate conductive element and temperature sensors exit from the coil arrangement.

Figure 7 is representative of the fluid flow in an embodiment of the present invention whereby the cooling channel is provided in a spiral configuration. Referring to Figure 7b which is representative of the patient facing side (2) the coolant enters chamber (12) via inlets (14). The coolant flows through inlet ports to create jets (48). These jets of coolant flow into the spiral cooling channel (22) and flow anticlockwise in the right hand cooling channel (22) and clockwise in the left hand cooling channel (22).

-13The coolant exits the spiral channel (22) at outlets (42) where the coolant continues to flow in the rotational direction of the spiral back to the outlet (26). The effect of the spiral is to cause more uniform flow and by directing the outlet (42) generally away from the outlet (26) coolant flow continues in the direction of the spiral and therefore increases uniformity of flow around the peripheral edge of the winding. The motion of the coolant flow around the peripheral edge as shown in Figure 7b causes the coolant flow on the non-patient facing side (4) of the winding to circulate more. It is possible that, as the exemplary embodiment in Figure 7 shows, there is a small amount of leakage flow from the chambers (12) from the non-patient side (4). This is shown and represented by reference numeral (60). Disposable circular pads (62) may be provided on the outer side of the housing (20) for hygiene purposes for different patients and a recess is provided in the housing (20) for receipt of the pads (62).

Referring now to Figure 8 the flow pattern for the same input flow rate of coolant viewed from the patient facing side of the winding is presented for an embodiment having 3 inlet ports and no spiral cooling channel configuration utilising water and oil as coolant in (a) and (b) respectively. Figures 8c and 8d are representative of the flow pattern utilising the spiral cooling channel configuration with water and oil as the coolant respectively.

Figures 8e, f, g and h show the steady state thermal map plotted on the coolant/tray (32) boundary as viewed from the patient facing side of the winding for the three inlet port model with water as the coolant, the three inlet port model with oil as the coolant, the spiral channel model with water as the coolant and the spiral channel model with oil as the coolant. Figure 8i, j, k and 1 show the steady state thermal map plotted on the outer housing (20) as viewed from the patient facing side of the magnetic stimulation coil arrangement for the three inlet port model with water as the coolant, the three inlet port model with oil as the coolant, the spiral channel model with water as the coolant and the spiral channel model with oil as the coolant. As can be seen in the case of using water as the coolant in the three inlet port model the effectiveness is high and the strong jets of water that are projected from the inlets cause flow (albeit over some parts of the casing (32)) around the majority of the casing (32). However, where flow is very weak and if the apparatus is left to run until steady state temperatures are achieved it can be seen that there

-14are small hot spots that may occur after some time on the patient facing surface of the housing (20). Other coolants such as fluourinert and synthetic transformer oil such as Midel 7131 tends to have a lower specific heat capacity and high viscosity than water. Therefore, their cooling efficiency tends to be much less than for water. It is noted, however, that these fluids are electrically inert. This does mean that the casing (32) can be removed and the coolant can flow in direct communication with the potting (30). In fact in the case of an electrically inert fluid the fluid may flow in direct communication with the windings (6). However in this case the windings do not poses the same mechanical strength and dielectric strength gained from potting them. Deionised water may but used but care must then be taken to ensure the water never becomes re-ionised such that it causes a hazard due to the high voltages involved in magnetic stimulation of tissue.

On reviewing the flow patterns when using Midel 7131, it is clearly seen to be extremely poor and due to the high viscosity it tends to flow straight back to the outlet (26). Typically these fluids can only be used to cool the apparatus when low level power is used to drive the coil arrangement under moderate protocols. By including the addition of the spiral channel the cooling efficiency for the synthetic oil is greatly increased and now is comparable to the winding temperature of the water cooled equivalent which is clearly presented in Figure 5. Accordingly, the use of a spiral configuration for the cooling channel enables either water or electrically insulating fluids to be used to cool a magnetic stimulation coil arrangement when operated during a harsh protocol.

The addition of the spiral cooling channel also acts to minimise patient surface hot spots due to better flow maps as can be seen in Figures 8k and 81.

Referring now to Figure 9, the effect on the materials selected for the casing (32) is shown. Plot lines (a) and (b) compare the provision of the casing (32) with high thermal conductivity and the effect it has upon the temperature of the windings. By selecting thermal conductivity of this casing (which may be termed a polymeric layer) of greater than one significantly improves the heat transfer away from the windings. Plot lines (c) and (d) represent the same effect utilising synthetic oil as a coolant and again show the

-15significant effect that the material selection of the casing (32) has upon the temperature of the windings.

Aspects of the present invention have been described by way of example only and will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims.

Claims

1. A magnetic stimulation coil arrangement for use in apparatus for the magnetic stimulation of tissue, the magnetic stimulation coil arrangement comprising one or more coil windings formed from an elongate conductive element, the one or more coil windings each wound to comprise a plurality of turns, and a housing for housing the one or more windings, wherein the magnetic stimulation coil arrangement further comprises a coolant flow pathway above and/or below the winding(s) and intermediate the winding(s) and the housing and being formed by one or more walls extending at least part way across a gap defined between the winding and the housing, the wall(s) forming a cooling channel that defines the coolant flow pathway where the coolant flow pathway extends in more than one direction.

2. A magnetic stimulation coil arrangement according claim 1 wherein the coolant flow pathway extends in a spiral configuration having a plurality of cooling channel turns.

3. A magnetic stimulation coil arrangement according to claim 2 wherein the cooling channel turns wind radially in the spiral configuration.

4. A magnetic stimulation coil arrangement according to any preceding claim wherein the winding has a patient facing side and an opposing upper side, and the cooling channel is provided toward the patient facing side.

5. A magnetic stimulation coil arrangement according to any preceding claim wherein the turns of the winding are positioned in a side by side configuration.

6. A magnetic stimulation coil arrangement according to any preceding claim wherein the one or more walls are positioned in a side by side configuration with the cooling channel therebetween.

7. A magnetic stimulation coil arrangement according to any preceding claim wherein the turns of the cooling channel extend outwardly from a radially inner inlet to a radially outer outlet.

8. A magnetic stimulation coil arrangement according to claims 2 and 7 wherein the outlet is arranged to direct coolant flowing therefrom in a direction as a continuum of the spiral configuration.

9. A magnetic stimulation coil arrangement according to any preceding claim wherein the magnetic stimulation coil arrangement comprises an inlet formation for directing coolant into the channel, the inlet formation comprising at least one inlet port configured to direct coolant radially outwardly.

10. A magnetic stimulation coil arrangement according to any preceding claim wherein the magnetic stimulation coil arrangement comprises an inlet formation for directing coolant into the channel, the inlet formation comprising multiple spaced apart inlet ports to the channel.

11. A magnetic stimulation coil arrangement according to claim 10 wherein the multiple inlet ports direct coolant into the first cooling channel turn.

12. A magnetic stimulation coil arrangement according to any of claims 2-11 comprising a first and a second winding, and wherein the cooling channel is provided in a first spiral configuration adjacent to the first winding and a second cooling channel adjacent to the second winding.

13. A magnetic stimulation coil arrangement according to any preceding claim wherein the one or more windings have a patient facing side and an upper side, where the coolant flow pathway extends between the peripheral edge of the one or more windings and the housing.

14. A magnetic stimulation coil arrangement according to claims 2 and 13 wherein the spiral configuration of the cooling channel terminates before the portion of the

-18coolant flow pathway between the peripheral edge of the one or more windings and the housing.

15. A magnetic stimulation coil arrangement according to any preceding claim wherein the one or more windings are provided with a potting material to encapsulate the turns of the winding.

16. A magnetic stimulation coil arrangement according to claim 15 wherein the thermal conductivity of the potting material is greater than 0.5 W/mK, and preferably greater than 1 W/mK.

17. A magnetic stimulation coil arrangement according to any of claims 15-17 wherein the one or more windings further comprises a polymeric layer arranged to cover the potting material.

18. A magnetic stimulation coil arrangement according to claim 17 wherein the thermal conductivity of the polymeric layer is greater than 0.5 W/mK, and preferably greater than 1 W/mK.

19. A magnetic stimulation coil arrangement according to claim 15 wherein the coolant flow pathway is defined directly between the potting material and the housing.

20. A magnetic stimulation coil arrangement according to claim 2 wherein the one or more coil windings may comprise a patient facing side and a non-patent facing side, and the coolant flow pathway extends between the housing and one or more coil windings on both the patient and non-patient facing sides, and wherein a first spiral configuration is provided on the patient facing side and a second spiral configuration is provided on the non-patient facing side.

21. A magnetic stimulation coil arrangement for use in apparatus for the magnetic stimulation of tissue, the magnetic stimulation coil arrangement comprising one or more coil windings formed from an elongate conductive element, the one or more coil windings each wound to comprise a plurality of turns wound in a radially outwardly direction, and a housing for housing the one or more windings, wherein

-19the magnetic stimulation coil arrangement comprises an inlet formation open to a coolant flow pathway intermediate the winding and the housing, the inlet formation having at least one inlet port for directing the coolant flow in the radially outwardly direction.

22. A magnetic stimulation coil arrangement according to claim 21 wherein the inlet formation has multiple spaced apart inlet ports to the channel.

23. A magnetic stimulation coil arrangement according to claim 22 wherein the multiple inlet ports are regularly spaced apart.

24. A magnetic stimulation coil arrangement according to any of claims 21-23 wherein the one or more windings have a patient facing side and an upper side, where the coolant flow pathway extends between the peripheral edge of the one or more windings and the housing.

25. A magnetic stimulation coil arrangement according to any of claims 21-24 wherein the one or more windings are provided in a potting material.

26. A magnetic stimulation coil arrangement according to claim 25 wherein the thermal conductivity of the potting material is greater than 0.5 W/mK and preferably greater than 1 W/mK.

27. A magnetic stimulation coil arrangement according to and of claims 25-26 comprising a polymeric layer arranged to cover the potting material.

28. A magnetic stimulation coil arrangement according to claim 27 wherein the thermal conductivity of the polymeric layer is greater than 0.5 W/mK, and preferably greater than 1 W/mK.

29. A magnetic stimulation coil arrangement according to claim 21 wherein the coolant flow pathway is defined directly between the potting material and the housing.