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`US007591776B2
`
`c12) United States Patent
`Phillips et al.
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 7,591,776 B2
`Sep.22,2009
`
`(54) MAGNETIC STIMULATORS AND
`STIMULATING COILS
`
`(75)
`
`Inventors: Mark Phillips, Lampeter Velfry (GB);
`Gary A. Thomas, Cardiff (GB)
`
`(73) Assignee: The Magstim Company Limited,
`Whitland, Dyfed (GB)
`
`( *) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 31 days.
`
`(21) Appl. No.: 10/999,574
`
`(22) Filed:
`
`Nov. 30, 2004
`
`(65)
`
`Prior Publication Data
`
`US 2006/0004244 Al
`
`Jan. 5, 2006
`
`(30)
`
`Foreign Application Priority Data
`
`Jul. 1, 2004
`Oct. 11, 2004
`
`(GB)
`(GB)
`
`................................. 0414909.2
`................................. 0422468.9
`
`(51)
`
`Int. Cl.
`A61N 1100
`(2006.01)
`(52) U.S. Cl. ............................................. 600/13; 600/9
`( 58) Field of Classification Search . ... ... ... ... .. 600/9-15;
`607/155, 152,100, 103-104
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,061,234 A *
`5,084,003 A
`5,116,304 A
`5,857,957 A *
`5,984,854 A *
`6,179,770 Bl*
`6,179,772 Bl*
`6,261,221 Bl
`
`10/1991 Chaney ....................... 600/14
`l/ 1992 Susie et al.
`5/ 1992 Cadwell
`1/1999 Lin ............................. 600/13
`1111999 Ishikawa et al.
`. ... ... ... ... .. 600/9
`1/2001 Mould ......................... 600/13
`1/2001 Blackwell .................... 600/13
`7/2001 Tepper et al.
`
`6,641,520 B2 *
`6,770,022 B2 *
`2001/0018547 Al
`2003/0158585 Al*
`
`11/2003 Bailey et al. .................. .
`8/2004 Mechlenburg et al.
`. ....... .
`8/2001 Mechlenburg et al.
`8/2003 Burnett ......................... .
`
`600/9
`600/9
`
`607/2
`
`FOREIGN PATENT DOCUMENTS
`
`GB
`GB
`WO
`WO
`WO
`
`2261820
`2298370
`WO 02/25675
`WO 02/31845
`WO 03/070317
`
`6/1993
`9/1996
`3/2002
`4/2002
`8/2003
`
`OTHER PUBLICATIONS
`
`Weyh T et al., "Marked differences in the thermal characteristics of
`figure-of-eight shaped coils used for repetitive transcranial magnetic
`stimulation", vol. 116, No. 6, Clinical Neurophysiology, Elsevier
`Science,
`Jun. 2005, pp. 1477-1486, XP004946514,
`ISSN:
`1388:2457.
`Al-Mutawaly Net al., "Designing and constructing a magnetic stimu(cid:173)
`lator: theoretical and practical considerations", vol. 1 of 4, Proceed(cid:173)
`ings of the 23rd Annual International Conference of the IEEE Engi(cid:173)
`neering in Medicine and Biology Society, 2001 Proceedings of the
`23rd Annual EMBS International Conference, Oct. 25-28, Istanbul,
`Turkey, Annual International Conference of the IEEE Engineering in
`M., pp. 881-884, XP010593517, ISBN: 0-7803-7211-5.
`
`* cited by examiner
`
`Primary Examiner-Charles A Marmor, II
`Assistant Examiner----Christine D Hopkins
`(74) Attorney, Agent, or Firm-Iandiori Teska & Coleman
`
`(57)
`
`ABSTRACT
`
`A stimulating coil for use in the magnetic stimulation of
`neuro-muscular tissue comprises a self-supporting but flex(cid:173)
`ible conductor in a flexible insulating sheath which can be
`adjusted by hand to conform the coil to the contours of a
`selected part of the human body. The coil is provided with a
`cooling system which includes a conduit disposed adjacent or
`within the coil and a pump for driving coolant through the
`conduit.
`
`7 Claims, 4 Drawing Sheets
`
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`Sep.22,2009
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`U.S. Patent
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`Sep.22,2009
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`US 7,591,776 B2
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`1
`MAGNETIC STIMULATORS AND
`STIMULATING COILS
`
`FIELD OF THE INVENTION
`
`This invention relates to magnetic stimulators, particularly
`for the magnetic stimulation of neuro-muscular tissue. Mag(cid:173)
`netic stimulators of this kind achieve stimulation by the cre(cid:173)
`ation of a rapidly changing magnetic field, for example of the
`order of 20 kilo Tesla per second in the vicinity of the tissue.
`Electric currents thereby induced in the tissue cause stimula(cid:173)
`tion thereof
`
`BACKGROUND TO THE INVENTION
`
`2
`may be driven. The coil could be molded within a flexible
`sheath which has an interface with a cooling jacket.
`According to another aspect of the invention a magnetic
`stimulating coil for the magnetic stimulation of neuro-mus-
`5 cular tissue comprises a flexible conductor in a flexible insu(cid:173)
`lating sheath which can be adjusted by hand to conform the
`coil to the contours of a selected part of the human body.
`The coil may be a multiple tum coil in which the turns are
`disposed to lie generally in a common plane and are supported
`10 by the flexible sheath in that configuration.
`The conductor may be provided with a cooling system as
`previously described.
`The invention will now be described in detail with refer-
`ence to a specific example and with recourse to the accom-
`15 parrying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Known magnetic stimulators comprise generally a charg(cid:173)
`ing circuit for a' discharge' capacitor, a discharge control such
`as a controlled rectifier for allowing discharge of the capacitor
`through the stimulating coil, and other circuit elements for
`limiting the effect of undesirable electrical transients. In
`known practice the coil may assume a variety of forms but
`typically comprise a rigid holder or a housing for a multi-turn
`coil which has appropriate connectors for coupling to the
`discharge circuit.
`The object of the invention is to allow a more versatile 25
`application of the stimulating technique and in particular to
`allow the coil to be formed around a patient's limb or other
`part of the human body, particularly to provide a large surface
`area which allows sub-maximal and super-maximal stimula(cid:173)
`tion of both superficial and deep muscles for the purposes of 30
`therapy or rehabilitation.
`
`FIG. 1 is a schematic circuit diagram of a magnetic stimu-
`20 lator.
`FIG. 2 is a schematic illustration of part of a coil cooling
`system
`FIG. 3 is a schematic diagram of one embodiment of the
`invention
`FIGS. 4, 5 and 6 are view ofa coil, shown from the rear, side
`and front respectively
`FIG. 7 is a schematic diagram showing the construction of
`a coil
`FIG. 8 is a diagram illustrating the flexure of the coil.
`
`DETAILED DESCRIPTION
`
`SUMMARY OF THE INVENTION
`
`According to one aspect of the invention, a magnetic stimu(cid:173)
`lator for the magnetic stimulation of neuro-muscular tissue
`comprises a stimulating coil, a charging circuit, a capacitor,
`and a discharge control for allowing discharge of the capaci-
`tor through the stimulating coil. The stimulating coil com(cid:173)
`prises a flexible conductor in a flexible insulating sheath 40
`which can be adjusted by hand to conform the coil to the
`contours of a selected part of the human body.
`Preferably the coil is wound into a multiple tum coil in
`which the turns are disposed to lie generally in a common
`plane and are supported by the flexible sheath in that configu(cid:173)
`ration. The sheath may have a generally flat disc shape.
`The sheath may include at least one sensor for sensing the
`temperature of the coil, and the sensor may be coupled, either
`directly or by way of a control circuit, to prevent current flow
`through the coil on the detection of a temperature above a
`limit. The measurement of temperature is to ensure that the
`possibly large area of the coil in close proximity to the patient
`does not produce a thermally hazardous condition.
`The conductor may be provided with a cooling system,
`preferably a system which drives coolant in proximity to the
`coil. For example the coil may be disposed in an outer tube,
`there being a pump for pumping a coolant through the outer
`tube so as to provide cooling of the conductor constituting the
`coil. The outer tube may be connected to a heat exchanger and
`the pump may be connected to recirculated the coolant 60
`through the heat exchanger and the outer tube. The coolant
`may be water but may be a liquid ofhigh thermal conductivity
`and low electrical conductivity and may be an organic ( car(cid:173)
`bon-based) liquid such as a fluorocarbon. Other forms of
`cooling system are feasible. For example, the whole coil may
`be immersed in a jacket containing coolant. The coil may be
`constituted by a hollow conductor through which coolant
`
`FIG. 1 of the drawings illustrates for the sake of complete-
`35 ness 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, commonly assigned herewith.
`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
`45 intervals is discharged into a stimulating coil 11. The transfer
`capacitor 5 is part of a charge pump which includes a unidi(cid:173)
`rectional 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 con-
`50 trolled rectifiers Sa, Sb, Sc and Sd. The discharge of the
`capacitor 9 is controlled by the switching system 10 compris(cid:173)
`ing controlled rectifiers 10a.10b.10c and 10d. The discharge
`current may be in either direction through the coil 11, which
`has an earth connection. Discharge pulses, of magnitude and
`55 frequency which are controllable by the 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; therms value of a typical pulse train may be hundreds
`of amps, such as 400 A.
`FIG. 2 illustrates some of the physical components of the
`system. They are the coil 11, which will be more fully
`described later, a flexible insulating conduit 12, a heat
`exchanger connection box 14 and a conduit 15. The ends of
`the coil inside their cooling tubes (to be described) pass
`65 through the conduit 12 to the box 14 and the coil ends pass
`through the conduit 15 to the rest of the stimulator as
`described with reference to FIG. 1. As will be described later,
`
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`US 7,591,776 B2
`
`3
`in this example the coil is disposed inside a flexible tube
`which conveys a fluid coolant.
`FIG. 3 illustrates the connections between the coil, the heat
`exchanger and the stimulator. The stimulator 16 is for
`example as described with reference to FIG. 1. The conductor 5
`lla constituting the electrical element of the coil 11 is con(cid:173)
`nected as shown in FIG. 1 to the remainder of the stimulator.
`The conductor is preferably self-supporting but flexible. It
`may (for example) be copper wire having a diameter in the
`range 2.5 to 3 mm. The conductor lla, which has an insulat- 10
`ing cover, forms the turns 18 of the coil of the coil 11. Over
`most of its length the conductor lla, which has an insulating
`cover (not shown) is enclosed in a flexible tube 17 which is
`connected to allow a pump 19 to pump fluid coolant through
`the tube 17 and a heat exchanger 20. In this embodiment there 15
`are two segments and to the tube, the conductor at its middle
`part llb coming out of one end of one tube segment and
`entering the other tube segment. Respective ends of the tube
`segments are connected to the pump and the heat exchanger.
`Thus in this example there are two parallel paths for coolant 20
`to flow adjacent the coil, one flow cooling the inner turns of
`the coil and the other flow cooling the outer turns of the coil.
`Coolant from the heat exchanger 20 flows to a reservoir 21
`connected to the pump 19 and is recirculated through the tube
`17 during the operation of the stimulator.
`FIGS. 4-6 are different views of the flexible cooled coil's
`general construction. The conductor lla in its tube extends
`along and within the flexible elongate conduit 15 which com(cid:173)
`prises two end connectors 12a and 12b and an intermediate
`part comprising a ribbed plastics tube 12c. The end connector
`12a is adapted in any convenient manner for connection to the
`connection box. The other end 12b is connected to a generally
`disc-shaped sheath 22 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 35
`illustrates a side view, showing the flat character of the sheath
`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 sheath 22 and close to its front surface are
`temperature sensors 23 with electrical connections 24 that 40
`extend back along the conduit to the stimulator. Shown sche(cid:173)
`matically is a safety switch 25 (FIG. 3) which in any conve(cid:173)
`nient marmer 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 45
`comprising the pump, heat exchanger, reservoir and the con(cid:173)
`necting 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 50
`avoided. By way of example a flow detector 26 within the
`coolant circuit is shown diagrammatically at 26 and is
`coupled to the safety switch 25.
`FIG. 7 illustrates the coil in section, the section being taken
`on the line X-X in FIG. 4.
`The coil, comprising the conductor lla and its surrounding
`tube 17 is encapsulated in the flexible, silicone rubber molded
`disc-shaped sheath 22. The tube 17 may be a silicone plastic
`material. The sheath 22 has on its rear side a bulge 26 which
`accommodates the lead-in and lead-out parts of the conductor 60
`in its tube 17. The coolant can flow along the space 27
`between the insulated conductor lla and the surrounding
`tube 17.
`
`4
`Other forms of cooling system may be employed. In the
`particular example, the outer tube is a conduit through which
`coolant is driven to cool the coil. However, the coil may be
`disposed adjacent or within a jacket through which coolant
`may be driven. The coil could be hollow and itself define a
`conduit through which coolant may be driven.
`FIG. 8 illustrates the flexing of the sheath 22 and thereby
`the coil 11 from a flat condition 11-1 thorough a moderately
`flexed condition to a fully flexed condition 11-3. The flexing
`of the head may be plastic, in that it will remain in the
`particular flexed state and not elastically revert to the flat
`un-flexed state. The amount of flexure may be chosen by an
`administrator to suit the contour or shape of the body part
`against which the coil is located. It may be necessary to
`employ straps or other holding means to locate the coil
`securely on the patient.
`Alternatively the flexure may be elastic; in this event the
`use of straps or other holding means is desirable to ensure that
`the coil is maintained in its flexed configuration and in posi(cid:173)
`tion on the patient.
`A variety of materials would be suitable for the sheath 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
`25 appropriate for an elastic sheath and a softer silicone rubber if
`the sheath is intended to flex plastically, the shape being
`maintained by the flexible copper wire inside the sheath.
`The invention claimed is :
`1. A magnetic stimulator for the magnetic stimulation of
`30 neuro-muscular tissue and comprising;
`a stimulating coil;
`a charging circuit;
`a capacitor; and
`a discharge control for allowing discharge of the capacitor
`through the stimulating coil; wherein the stimulating
`coil comprises a flexible conductor enclosed in a flexible
`tube, the flexible tube for allowing the passage of cool(cid:173)
`ant, the stimulating coil being in a flexible insulating
`sheath having a generally flat disc shape which can be
`adjusted by hand to conform the coil to the contours of a
`selected part of the human body, said flexible conductor
`and flexible tube being wound into a multiple tum coil in
`which the turns are disposed to lie generally in a com(cid:173)
`mon plane and are supported by the flexible sheath in
`that plane, and wherein the stimulator further comprises
`a pump for driving coolant through the flexible tube.
`2. A stimulator as in claim 1 wherein said sheath includes
`at least one sensor for sensing the temperature of the coil, and
`said sensor is coupled to prevent current flow through the coil
`on the detection of a temperature above a limit.
`3. A stimulator as in claim 1 wherein the flexible tube is
`connected to a heat exchanger and said pump is connected to
`recirculate the coolant through the heat exchanger and the
`flexible tube.
`4. A stimulator as in claim 1 wherein said coolant is a liquid
`of high thermal conductivity and low electrical conductivity.
`5. A stimulator as in claim 1 wherein said coolant com(cid:173)
`prises water.
`6. A stimulator as in claim 1 wherein said sheath is plasti(cid:173)
`cally flexible.
`7. A stimulator as in claim 1 wherein said sheath is elasti(cid:173)
`cally flexible.
`
`55
`
`* * * * *
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