GB2459157A

GB2459157A - Magnetic stimulation device with stimulating coil cooled in two sections

Info

Publication number: GB2459157A
Application number: GB0806999A
Authority: GB
Inventors: Mark Phillips
Original assignee: Magstim Co Ltd
Current assignee: Magstim Co Ltd
Priority date: 2008-04-17
Filing date: 2008-04-17
Publication date: 2009-10-21
Anticipated expiration: 2028-04-17
Also published as: GB0806999D0; WO2009127840A1; GB2459157B

Abstract

A magnetic stimulator for the magnetic stimulation of brain or muscular tissue including a stimulating coil device 11, a stimulator 11 with charging circuit (fig 1) comprising a capacitor and discharge control means, and a cooling system. A coolant supply system comprises a pump supplies coolant to the stimulating coil device via conduits 17, 18 which return to a heat exchange means 20. The coil device has an inner coil 12 and an outer coil 13 with an inner coil conduit 17 and outer coil conduit 18. The coolant supply system is configured to supply coolant to the inner coil in a first flow direction B and simultaneously supply coolant to the outer coil in an opposite second flow direction A. The coils are flexible and a generally flat disc shape (figs 3 to 6). For patient safety, temperature sensors (23 fig 6) may disable the stimulator if the coil temperature is too high and flow sensors 26 may detect if coolant flow it too low.

Description

MAGNETIC STIMLJLATORS ANT) STIMULATING COILS

Field of the Invention

This invention relates to magnetic stimulators, particularly for the magnetic stimulation of brain and/or muscular tissue. Magnetic stimulators of this kind achieve stimulation by the creation of a rapidly changing magnetic field, for example of the order of 20 kiloTesla per second in the vicinity of the tissue. Electric currents thereby induced in the tissue cause stimulation thereof

Background to the invention

Known magnetic stimulators generally comprise a charging circuit for a "discharge" capacitor, a discharge control such as a controlled rectifier for allowing discharge of the capacitor through a stimulating coil, and other circuit elements for limiting the effect of undesirable electrical transients. Heat is generated in the stimulating coil during use so * *. the coil generally requires cooling to ensure comfort for the patient. GB 2415632 describes a known magnetic stimulator with cooling system. *S..

An object of the invention is to provide effective cooling for a magnetic stimulator. **S* *. 20

*:::: Summary of the invention

S.....

* * According to one aspect of the invention, a magnetic stimulator for the magnetic stimulation of neuro-muscular tissue comprises: a stimulating coil device; a charging circuit; a capacitor; a discharge control for allowing discharge of the capacitor through the stimulating coil device; and a coolant supply system which supplies coolant to the stimulating coil device; wherein the stimulating coil device comprises an inner coil and an outer coil and the cooling system is configured to supply coolant to the inner coil such that the coolant flows in a first flow direction to cool the inner coil and to simultaneously supply coolant to the outer coil such that the coolant flows in an opposite second flow direction to cool the outer coil.

The applicants have found that the cooling configuration of the invention provides particularly effective cooling.

According to another aspect of the invention a magnetic stimulating coil device for the magnetic stimulation of neuro-muscular tissue comprises: an inner coil; and an outer coil; wherein the inner and outer coils each comprise a coolant conduit configured for separate connection to a coolant supply system such that coolant can simultaneously flow in a first direction through the coolant conduit of the inner coil and in an opposite direction through the coolant conduit of the outer coil.

According to a further aspect of the invention, a method of cooling a magnetic stimulating coil device, the magnetic stimulating coil device being for the magnetic stimulation of neuro-muscular tissue, comprises the step of supplying coolant in a first * ** flow direction to an inner coil of the magnetic stimulating coil device and simultaneously supplying coolant to an outer coil of the magnetic stimulating coil in an opposite flow direction. : 20

Preferably the inner and outer coils each have an associated coolant conduit, the coolant conduits being separately connected to the coolant supply system and more preferably *: ::* each coolant conduit comprises a flexible hollow member. *

The inner and outer coils may comprise a flexible conductor which extends through the respective flexible hollow members.

The inner and outer coils may be multiple turn coils, with both the flexible conductor and the flexible hollow members through which the flexible conductor extends being wound in multiple turns. The turns of both the inner and outer coils are preferably disposed to lie generally in a common plane. The coils may be embedded in a flexible cover comprising a flexible covering material, which is preferably an insulating material.

Preferably the coils and the flexible cover can be adjusted by hand to conform the coil to the contours of a selected part of the human body.

Preferably the inner and outer coils each comprise a multiple turn coil in which the turns are disposed to lie generally in a common plane and are supported by the flexible cover in that plane.

Preferably the flexible cover includes at least one sensor for sensing the temperature of the coil or coils, and said sensor is coupled to prevent current flow through the coils on the detection of a temperature above a limit.

Preferably the flexible cover is plastically flexible or elastically flexible.

Preferably the flexible cover has a generally flat disc shape.

Preferably the coolant conduits are connected to a heat exchanger or peltier device and a pump is connected to recirculate the coolant through the heat exchanger/peltier device and the coolant conduits. *S..

The coolant may be water but may be a liquid of high thermal conductivity and low electrical conductivity and may be an organic (carbon-based) liquid such as a * fluorocarbon. Alternatively the coolant could be a gas. *

* ** Exemplary embodiments of the invention will now be described in detail with reference 20 to the accompanying drawings.

* S. S S S * .

Brief Description Of The Drawings

FIG. 1 is a schematic circuit diagram of a magnetic stimulator; FIG. 2 is a schematic diagram of a magnetic stimulator in accordance with the invention; FIG. 3 schematically shows a cross-section through the embodiment of Fig 2 or Fig. 4.

FIG.'s 4, 5 and 6 represent views of a coil, shown from the rear, side and front respectively.

Detailed Description

FIG. 1 of the drawings illustrates for the sake of completeness the electrical circuit of one form of magnetic stimulator suitable for use in the present invention. The particular example is one of several different stimulators which are the subject of, and are more fully described in, U.S. Pat. No. 5,766,124 to Polson.

This particular example has a high-voltage power supply 1 which charges a reservoir capacitor 2. Charge is transferred from the reservoir capacitor, substantially independently of the charging rate of the reservoir capacitor, via a transfer capacitor 5 to a discharge' capacitor 9, which at appropriate intervals is discharged into a stimulating coil 11. The transfer capacitor 5 is part of a charge pump which includes a unidirectional switch 3, a series inductor 4, the transfer capacitor 5, a reverse diode 6 in parallel with the capacitor 5, a series inductor 7 and a switching system 8, which comprises controlled rectifiers 8a, 8b, 8c and 8d. The discharge of the capacitor 9 is controlled by the switching system 10 comprising controlled rectifiers lOa, lOb, lOc and lOd. The * discharge current may be in either direction through the coil 11, which has an earth s' *. connection. Discharge pulses, of magnitude and frequency which are controllable by the 5.s switching systems 8 and 10, flow through the coil 11. Typically the instantaneous current may be of the order of 5 kA, i.e. considerably in excess of 1 kA; the rms value of a 5** * typical pulse train may be hundreds of amps, such as 400 A. *5*

S

* FIG. 2 illustrates the physical components of an embodiment of the magnetic stimulator.

The magnetic stimulating coil device 11 comprises inner coil 12 and outer coil 13. The inner coil 12 comprises a flexible conductor 1 la disposed inside an elongate flexible tube 17 which conveys a fluid coolant. The outer coil 13 comprises a flexible conductor 11 a disposed inside elongate flexible tube 18. The flexible conductor 11 a may (for example) be copper wire having a diameter in the range 2.5 to 3 mm. In this embodiment, the middle region 1 lb of the flexible conductor exits tube 17 before tube 17 connects with the heat exchanger and enters tube 18 before tube 18 connects with the heat exchanger.

The conductor 11 a is preferably self-supporting and preferably has an insulating cover (not shown). The conductor 11 a constituting the electrical element of the magnetic coil stimulating device 11 is connected as shown in FIG. I to the remainder of the stimulator.

The stimulator 16 is for example as described with reference to FIG. 1.

Respective ends of the flexible tubes 17 and 18 are connected to the pump 19 and the heat exchanger or pettier device 20. The flexible tubes 17 and 18 are connected to allow a pump 19 to simultaneously pump fluid coolant through the tubes 17 and 18 such that, in use, the direction of flow in the tubes is opposed, as indicated by the arrows A and B. Thus if the coolant flow in tube 17 is clockwise then the flow in tube 18 will be anti-clockwise. Alternatively the system could be configured so that the coolant flow in tube 17 was in an anticlockwise direction whilst the flow in tube 18 was in a clockwise direction. The coolant fluid then enters a heat exchanger or a pettier device shown at 20.

Coolant from the heat exchanger or peltier device 20 flows to a reservoir 21 connected to the pump 19 and is recirculated through the tubes 17 and 18 during the operation of the stimulator.

FIG. 3 illustrates the coil in section, the section being taken on the line X-X in FIG. 2 or * ** FIG4 * S. *S.. * . *S..

* : The inner 12 and outer 13 coils, comprising the wound conductor 11 a and its surrounding wound flexible tubes 17 and 18 are encapsulated in the flexible, silicone rubber moulded S..

* disc-shaped cover 22. The tubes 17 and 18 may be a silicone plastic material. The cover *: :: 22 has on its rear side a bulge 26 which accommodates the lead-in and lead-out parts of the flexible conductor 11 a in its tubes 17 and 18. The coolant flows along the space 27 * between the conductor 1 la and the surrounding tube 17 or 18. As previously mentioned above the flexible conductor may have an insulating and coolant resistant coating.

FIGS. 4-6 are different views of the cooled coil's general construction. The conductor 11 a in the tubes 17 and 18 extends along and within the flexible elongate conduit 32 which comprises two end connectors 32a and 32b and an intermediate part comprising a ribbed plastics tube 32c. The end connector 32a is adapted in any convenient manner for connection to the connection box. The other end 32b is connected to a generally disc-shaped flexible covering material within which the turns of the coil are located in the same plane. FIG. 4 illustrates the rear' of the coil, i.e. that which faces away from the patient in use. FIG. 5 illustrates a side view, showing the flat character of the covering material 22 in its original unflexed state. FIG. 6 illustrates the coil head form the front, i.e. that which is adjacent the patient in use.

Embedded in the flexible cover 22 and close to its front surface are temperature sensors 23 with electrical connections 24 that extend back along the conduit to the stimulator.

Shown schematically is a safety switch 25 (FIG. 2) which in any convenient manner can disable the stimulator, to prevent current flow through the coil, if the sensed temperature is too high.

There may be flow detectors within the coolant circuit comprising the pump, heat exchanger, reservoir and the connecting conduits. Accordingly if the coolant flow reduces to below some pre-set value the application of current to the stimulating coil would be * prevented. This is another safety feature to ensure that a thermally hazardous condition is avoided. By way of example a flow detector 26 within the coolant circuit is shown *,..

*** 20 diagrammatically at 26 and is coupled to the safety switch 25.

S

* Other forms of cooling system may be employed within the scope of the present invention. Rather than having the conductor disposed in the coolant conduit as * * specifically described, the multiple windings of the inner coil may be disposed within one * : * 25 single outer tube whilst the multiple windings of outer coil may also be disposed within another single outer tube with the coolant being driven simultaneously in opposing directions through the outer tubes. Alternatively the inner and outer coils may be disposed adjacent cooling conduits through which coolant is driven in opposing directions. In a further alternative embodiment, the conducting elements of the inner and outer coils could be hollow and define conduits through which coolant may be driven simultaneously in opposite directions.

A variety of materials would be suitable for the cover 22. A silicone rubber compound may be used. The degree of hardness of the rubber may be chosen according to the desired elasticity of the flexure; a hard silicone rubber would be appropriate for an elastic covering material and a softer silicone rubber if the covering material is intended to flex plastically, the shape being maintained by the flexible copper wire inside the sheath. * .* * * * * *S * * **** **S*

S S... * .. * . S * S.

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Claims

Claims 1. A magnetic stimulator for the magnetic stimulation of brain or muscular tissue comprising: a stimulating coil device; a charging circuit; a capacitor; a discharge control for allowing discharge of the capacitor through the stimulating coil device; and a coolant supply system which supplies coolant to the stimulating coil device; wherein the stimulating coil device comprises an inner coil and an outer coil and the coolant supply system is configured to supply coolant to the inner coil such that the coolant flows in a first flow direction to cool the inner coil and to simultaneously supply coolant to the outer coil such that the coolant flows in an opposite second flow direction to cool the outer coil.
2. A magnetic stimulator according to claim 1 wherein the inner and outer coils each have an associated coolant conduit, the coolant conduits being separately connected to the * ** * * coolant supply system. ***. ***.

:
3. A magnetic stimulator according to claim 2 wherein each coolant conduit comprises a flexible hollow member. * S.
4. A magnetic stimulator according to claim 3 wherein the inner and outer coils S.....* 25 comprise a flexible conductor which extends through the respective flexible hollow members.
5. A magnetic stimulating coil device for the magnetic stimulation of brain or muscular tissue, the stimulating coil device comprising: an inner coil; an outer coil; wherein the inner and outer coils each comprise a coolant conduit configured for separate connection to a coolant supply system such that coolant can simultaneously flow in a first direction through the coolant conduit of the inner coil and in an opposite direction through the coolant conduit of the outer coil.
6. A magnetic stimulating coil device according to claim 5 wherein each coolant conduit comprises a flexible hollow member.
7. A magnetic stimulating coil device according to claim 6 wherein the inner and outer coils comprise a flexible conductor which extends through the respective flexible hollow member.
8. A method of cooling a magnetic stimulating coil device, the magnetic stimulating *. *. * coil device being for the magnetic stimulation of brain or muscular tissue, the method *** S * ... 20 comprising the step of supplying coolant in a first flow direction to an inner coil of the * magnetic stimulating coil device and simultaneously supplying coolant to an outer coil of S...* the magnetic stimulating coil in an opposite flow direction. *.SS*
9. A magnetic stimulator andlor a magnetic stimulating coil device andlor a method of cooling a magnetic stimulating coil device substantially as hereinbefore described and with reference to the accompanying drawings.