(12) INPERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
` =
`
`WIPO/PCT
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`(43) International Publication Date
`02 November 2017 (02.11.2017)
`
`UNDE UTA MUUUTTA
`
`(10) International Publication Number
`WO 2017/187184 Al
`
`(51)
`
`@)
`
`International Patent Classification:
`
`A6IN 2/02 (2006.01)
`
`A61N 2/00 (2006.01)
`
`International Application Number:
`PCT/GB2017/051190
`
`(22)
`
`International Filing Date:
`
`28 April 2017 (28.04.2017)
`.
`English
`English
`
`.
`eye
`(25) Filing Language:
`(26) Publication Language:
`(30) Priority Data:
`.
`.
`GB
`28 April 2016 (28.04.2016)
`1607384.3
`(71) Applicant: THE MAGSTIM COMPANY LIMITED
`[GB/GB]; Whitland Industrial Estate, Spring Gardens,
`Whitland Dyfed SA34 OHR (GB).
`
`(72)
`
`(74)
`
`Inventor: BIGINTON, Matthew; c/o The Magstim Com-
`pany Limited, Whitland Industrial Estate, Spring Gardens,
`Whitland Dyfed SA34 OHR (GB).
`
`Agent: BAKER, Thomas Edward; Urquhart-Dykes &
`Lord LLP, 7th Floor, Churchill House, Churchill Way,
`Carditt South Glamorgan CF 10 2HH (GB).
`
`(81) Designated States (unless otherwise indicated, for every
`kind ofnational protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW,BY, BZ,
`CA, CH, CL, CN, CO, CR, CU, CZ, DE, DJ, DK, DM, DO,
`DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN,
`HR, HU,ID,IL,IN,IR,IS, JP, KE, KG, KH,KN, KP, KR,
`KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM,
`PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, SC,
`
`(54) Title: MAGNETIC STIMULATION COIL ARRANGEMENT
`
`“
`
`wen,>
`
`at
`
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`(57) Abstract: The present invention relates to a magnetic stimulation (84S) coil arrangement whichutilises the effect of the position
`of a ferromagnetic material to enhance the magnetic field on the patient side of the coil and reduce acoustic noise associated with the
`addition of ferromagnetic material. The present invention comprises a magnetic stimulation coil arrangement comprising one or more
`coil windings formed from an elongate conductive element and having a forward side for presentation to a patient and a rearward side,
`the magnetic stimulation coil arrangement further comprising a distortion arrangementfor distorting a magnetic field produced by the
`one or more coils positioned adjacent to the rearward side, the distortion arrangement having a plurality of ferromagnetic components
`and a carrier for carrying the ferromagnetic components, the ferromagnetic components being spaced from one anotherbythecarrier.
`
`[Continued on next page]
`
`
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`wo2017/187184A.MININGAEAA
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`

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`WO 2017/187184 A IAITIITTE TAMA AUT TTAO M
`
`SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR,
`TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM,KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ,
`UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE, ES, FI, FR, GB, GR, HR, HU,IE, IS, IT, LT, LU, LV,
`MC, MK, MT,NL, NO,PL, PT, RO, RS, SE, SI, SK, SM,
`TR), OAPT(BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW,
`KM, ML, MR, NE, SN, TD, TG).
`
`Published:
`
`— with international search report (Art. 21(3))
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`

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`WO 2017/187184
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`PCT/GB2017/051190
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`-|-
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`MagneticStimulationCoilArrangement
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`The present invention relates to a Magnetic Stimulation (MS) coil arrangement which
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`utilises the effect of the positioning of a ferromagnetic material to enhance the magnetic field
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`Ai
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`on the patient side of the coil and reduce acoustic noise associated with the addition of
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`ferromagnetic material.
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`MScoil arrangements include an apparatus for transmitting at least one pulse of current
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`through a generally circular coil or a figure of eight coil arrangement having one or more
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`10
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`windings, each having a plurality of turns. MS coils can be producedin a variety of shapes
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`sizes and arrangements. Typical stimulating coils comprise an elongate conductive element
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`woundinto a coil having a plurality of turns wherebythe turns are insulated from each other.
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`Whena current is passed through the wound elongate conductive element the magnetic field
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`that is generated transfers to a patient to give a therapeutic effect or to research how various
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`15
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`parts of the brain or body operate.
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`Figure 1 (a) is a three dimensional schematic representation of a circular MS coil (1)
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`comprising a coil winding (3) having a plurality of turns. The centre (symmetry)line of
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`the coil is marked with a dashed line (5). The coil (1) is connected to a stimulator (not
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`20
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`shown) via the two ends of the coil winding (7). Figure 1 (b) shows a double TMScoil (or
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`Figure of eight TMS coil) comprising two coil windings(3) to showthe variety of different
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`coils available. Each winding (3) typically has an opening (or hole) (9) at its centre.
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`Figure 1(c) shows across section of the turns of a circular winding showing the individual
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`turns (11).
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`25
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`Figure 2 is a cross sectional view of the circular MS coil (1) shown in Figure 1(a) and (c)
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`with varying sized and shaped ferromagnetic slabs (discs in this example) (13) placed on
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`the operator (rearward)side of the coil. Figure 2 (a), (b), (c) and (d) show 2mm, 4mm,
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`8mm and 16mm thick slabs respectively placed on the back of the circular coil.
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`In Figure
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`30
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`2 (e) the ferromagnetic material has been extended (12) into the aperture (9) of the winding
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`and around the peripheral cdges of the coil (1).
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`WO 2017/187184
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`PCT/GB2017/051190
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`By positioning a ferromagnetic material (13) behind the coil (1) the magnetic field in
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`comparison to the circular coil (1) alone as (illustrated by finite element modelling in Figure
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`3(b)) is distorted and is now asymmetric about the plane of the coil. The reluctance of the
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`material on the rearward side of the coil (1) is now significantly lower and as a result most
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`of the energy delivered to the coil is now stored in the volume on the forward side of the
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`coil. This means that for the same applied energy the magnetic field strength is higher on
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`the forwardside of the coil (in the patient’s tissue). Alternatively, the same magnetic field
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`10
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`strength may be supplied to the patient whilst using less energy in comparison to the coil
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`without the ferromagnetic material. This meansthat not only less energy is used to drive the
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`coil but less joule heating occurs in the coil windings and can increase the amount of
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`stimulations the coil can perform before overheating.
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`15
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`Figure 3 (a) and (b) are a comparison of the finite element modelled magnetic field contour
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`lines around the circular MS coil (1) shown in Figure | (a) and the circular MS coil shown
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`in Figure 1 (d) with a 16mm thick disc of ferromagnetic material placed adjacent its
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`rearward side.
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`In both casesthe field lines are shown on the symmetryplane (5) illustrated
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`in Figure 1(a). As can be clearly seen the field strength on the patient side (forward side)
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`20
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`of the coil is increased by a significant amount. For clarity a dotted line outlines the
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`ferromagnetic disc.
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`Figure 4 illustrates the effect of increasing disc thickness of the ferromagnetic material
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`(13) from 2mm to 16mm. As can be seen from the modelled contour maps the field
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`25
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`strength on the patient side of the coil (1) is higher in comparison to the circular coil when
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`the 2mmdisc is placed on the rearward side of the coil presented in figure 4a. Having a
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`4mmlayerincreases the field strength further (b), 8mm further again (c) and 16mm further
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`still (d). In the case of the 16mm layer the increase has nearly levelled off and any further
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`increase in layer thickness will have only a marginal effect on field enhancement.
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`30
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`Figure 5 (a) and (b) compare the ficld contour lines for a thick 16mm disc of ferromagnetic
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`material (shown in Figure 2 (d)) and the same disc albeit with the ferromagnetic material
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`-3-
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`extending downinto the coil winding aperture (9) and around the periphery of the coil (1).
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`Clearly there is a greater increase in field strength with the extended sections (15, 12) of
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`ferromagnetic material.
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`Finite element results shown in Figures 3, 4 and 5 are modelled on a 2D plane in a 2D
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`asymmetric model in COMSOLmulti-physics which predicts the solutions assuming
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`azimuthal symmetry.
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`Figure 6 illustrates the magnetic field pulse waveforms from finite element modelling as
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`10
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`recorded 2cm beneath the turns of the MS coil winding. Reference numerals 20, 21, 22,
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`23, 24 and 25 show the waveformsforthe field distortion arrangements shown in Figure 2
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`(a), (b), (c), (d) and (e) respectively again illustrating that a thicker ferromagnetic materials
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`on the back of the coil (1) produces an increased field strength at the front of the coil (1).
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`In addition the plot clearly shows the benefit of extending the ferromagnetic material into
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`15
`
`the aperture (9) of the coil (1) around the peripheral edges.
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`There are problems associated with positioning a ferromagnetic material adjacent the coil at
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`the operator’s side. A solid ferromagnetic (metal) plate for example generates significant
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`Eddy currents and quickly heats up. This significantly limits the numberof pulses of current
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`20
`
`that may be supplied through the coil before the plate becomes too hot.
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`In addition these
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`eddy currents tend to reducethe benefits from placing a ferromagnetic metal aroundthe coil
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`as described in patent WO2016/005719.
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`An alternative ferromagnetic material has previously been utilised comprising grains of iron
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`25
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`of approximately 0.1mm in diameter, each electrically insulated from an adjacent grain by a
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`very thin inorganic insulation material. These insulated grains are then sintered and
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`subsequently cut to the desired shape. A problem that exists with the provision of sintered
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`encapsulated iron grains is this material, as with many other ferromagnetic materials may
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`becomesaturated in particular for the case of smaller MS coils which tend to produce much
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`30
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`higher magnetic flux densities than their larger counterparts. This means anincrease in the
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`applied external magnetic ficld cannot significantly incrcasc the magnctisation of the
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`material further so the total magnetic flux density levels off. This means that the magnetic
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`WO 2017/187184
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`PCT/GB2017/051190
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`4.
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`treatmentfield is not as high as intended or selected as the ferromagnetic material is no
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`longer acting as such, and thus has less effect upon the magnetic field produced.
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`Furthermore, upon saturation the temperature of the material may increase rapidly thus
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`meaning that operation of the magnetic stimulation arrangement must be paused. This is
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`Ai
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`particularly relevant for magnetic stimulation of a patient whereby the desirable magnetic
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`flux density may typically be as high as three Tesla at somelocations near the coil.
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`A second problem that exists with placing electrically insulated grains as described above
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`and solid plates of ferromagnetic material on the operator side of a TMScoilis that they tend
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`10
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`to enhance not only the magnetic field on the patient side of the coil but also the noise
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`generated from the magnetic stimulation coil arrangement. This is considered to be an
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`adverse effect as it is typical for patients to have to wearear protection with standard TMS
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`coils and additional noise is therefore undesirable for both patient and operator.
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`15
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`The present invention provides an improved solution whichis easily implemented, cheap,
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`effective and in particular aids in reducing the noise produced by the magnetic stimulation
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`coil arrangement solving the second problem with the priorart.
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`According to the present invention there is a magnetic stimulation coil arrangement for use
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`20
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`in apparatus for
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`the magnetic simulation of Ussue,
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`the magnetic simulation coil
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`arrangement comprising one or more coil windings formed from an elongate conductive
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`element and having a forward side for presentation to a patient and a rearward side, the
`
`magnetic stimulation coil arrangement further comprising a distortion arrangement for
`
`distorting a magnetic field produced by the one or more windings positioned adjacent to the
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`25
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`rearward side, the distortion arrangement having a plurality of ferromagnetic components
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`and a carrier for carrying the ferromagnetic components, the ferromagnetic components
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`being spaced from one anotherby the carrier.
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`The provision of the ferromagnetic components being spaced from one another and
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`30
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`beneficially electrically insulated from one another causesthe distortion arrangement to have
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`a lower permeability duc to the provision of the spacings (cffcctively air gaps). This
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`typically allows the ferromagnetic components to withstand a higher applied external
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`-5-
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`magnetic field strength before saturating. The present invention typically will have a lower
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`permeability than either solid metal or encapsulated grains of iron in the known material
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`“Somaloy”, which maysaturate at a too low a flux density and which in some cases can lead
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`to overheating. This leads to significant downtime as cooling of the distortion arrangement
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`Ai
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`is required between pulses.
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`The ferromagnetic components are retained in the carrier through being encapsulated and/or
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`embeddedin the carrier. The carrier is a solid at room temperature and pressure.
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`10
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`The carrier is beneficially a matrix in which the ferromagnetic components are dispersed.
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`The ferromagnetic components are beneficially randomly dispersed in the matrix.
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`Dispersion of ferromagnetic components in the matrix reduces manufacturing costs whilst
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`also providing the beneficial properties of the distortion arrangement.
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`15
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`The carrier is beneficially an electrical insulator and may comprise a polymer or ceramic.
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`The term component means a manufactured or formed object. Examples of components are
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`ball bearings, nuts, bolts, discs, rods, cubes or parts of such objects. This improves ease and
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`cost effectiveness of manufacture of the distortion arrangement.
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`20
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`The ferromagnetic components are beneficially dispersed within the carrier such that the
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`distortion arrangementsaturates at an applied field generating a flux density of greater than
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`1.5 Tesla.
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`25
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`The distortion arrangementis preferably positioned adjacent to and preferably parallel to the
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`rearwardside.
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`The distortion arrangement preferably comprises an array of ferromagnetic components.
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`The ferromagnetic components are beneficially regularly spaced within the array for ease
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`30
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`and repeatable manufacturing. However they may be randomly spaced. The ferromagnetic
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`components are bencficially embedded or encapsulated in the carricr. The array may be an
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`ordered array, however for ease of manufacture the ferromagnetic components in the array
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`-§-
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`may be randomly positioned and oriented. This may be achieved by simply mixing the
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`ferromagnetic components in the carrier provided in flowable form and allowing the carrier
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`to set in a mould of the desired shape.
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`The distortion arrangement preferably includes a plurality of ferromagnetic components
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`having matching dimensions for ease of manufacture. However it is appreciated that non
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`matching dimensions or shapes will have a similar effect. The ferromagnetic components
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`are beneficially manufactured or formed components. A plurality of the ferromagnetic
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`components preferably have the same dimensions.
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`The plurality of ferromagnetic
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`10
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`components are preferably substantially identical. The provision of spherical ferromagnetic
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`components provides a cheap and readily available ferromagnetic component that may be
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`easily positioned in a carrier.
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`The maximum dimension of the ferromagnetic components is preferably between 0.045 and
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`15
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`lem. The maximum dimensionis preferably less than 3cm as it will be appreciated that as
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`the size of ferromagnetic component significantly increases and progresses beyond 2cm then
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`more significant eddy currents are induced in the ferromagnetic components thus leading to
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`the heating of the distortion arrangement. A lower limit dimension of approximately
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`0.045cm is beneficial as lower than this means that it is difficult to maintain sufficient
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`20
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`separation gap between ferromagnetic componentsleading to saturation at a too low a value
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`of externally applied magnetic field strength thus reducing or removing the beneficial
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`properties of the distortion arrangement.
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`The array may comprisea single layer of ferromagnetic components.
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`25
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`The array may comprise multiple layers of ferromagnetic components.
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`The carrier between the ferromagnetic components is preferably chosen to dampen the sound
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`produced from the distortion arrangement and mechanically hold the ferromagnetic
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`30
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`components in situ.
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`-7-
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`Typically the average spacing between ferromagnetic components may be 1/10 the size of
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`the ferromagnetic components. However it is appreciated that by varying the gap size
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`between the ferromagnetic components will change the effective permeability of the
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`distortion arrangement. Therefore this average gap size could be as large as 3/1. The average
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`Ai
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`gap may be as small as 1/25 in the case of 0.045cmferromagnetic component and 1/500 in
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`the case of the largest ferromagnetic components (83cm).
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`It will be appreciated that there
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`may be some touching of ferromagnetic components, particularly when mixed in size and/or
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`shape howeverit is preferable that this is minimised.
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`10
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`The array may comprise a three dimensional array and the ferromagnetic components may
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`be randomly spaced in the array. By providing a randomly spacedplurality of ferromagnetic
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`componentsin the carrier the ferromagnetic components may be simply mixed in the carrier
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`and formed in a mould providing the distortion arrangement.
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`15
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`The distortion arrangement may be arranged to correspond to the shape of the rearward side
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`of the one or more coil windings. The distortion arrangement may comprise one or more
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`apertures therein, each of the one or more apertures arranged to be aligned with
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`corresponding apertures found radially inwardly of the elongate conductive element forming
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`the one or more windings.
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`20
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`The or each of the coil winding preferably comprises a radially inner aperture, and the
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`distortion arrangement may comprise a projection arranged to extend into the aperture. This
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`has been found to further improvethe effectiveness of the distortion arrangement.
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`25
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`The rearward side of the one or more windings comprises a peripheral edge, and the
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`distortion arrangement may comprise a lip that extends around at least a portion of the
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`peripheral edge. This again further improvesthe effectiveness of the distortion arrangement.
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`The ratio of the volume of ferromagnetic components to carrier material in the distortion
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`30
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`arrangement is preferably less than 1.5:1, and preferably less than 1:1.
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`

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`WO 2017/187184
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`-2-
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`According to a second aspect of the present invention there is a magnetic stimulation coil
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`arrangement for use in apparatus for the magnetic stimulation of tissue,
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`the magnetic
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`stimulation coil arrangement comprising one or more coil windings formed from an elongate
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`conductive element and having a forward side for presentation to a patient and a rearward
`
`Ai
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`side, the magnetic stimulation coil arrangement further comprising a distortion arrangement
`
`for distorting a magnetic field produced by the one or more coils positioned adjacent to the
`
`rearward side, the distortion arrangement having a plurality of ferromagnetic particles and a
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`carrier for carrying the ferromagnetic particles, the ferromagnetic particles being spaced
`
`from one anotherby the carrier wherein the ratio volume of ferromagnetic particles to carrier
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`10
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`material is less than 1.5:1.
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`This provides the advantage that noise is effectively attenuated whilst most of the energy
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`delivered to the coil is now stored in the volume on the forwardside of the coil.
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`15
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`The ratio of the volume of ferromagnetic particles to carrier material is preferably less than
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`1:1.
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`The ferromagnetic particles may for example comprise ironfilings.
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`20
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`Preferred features of the first aspect should also be understood as being preferred features of
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`the second aspect.
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`The present invention will now be described by way of example only with reference to the
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`accompanying drawings in which:
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`25
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`Figure la is a three dimensional representation of a magnetic stimulation coil winding,
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`figure 1b is a double TMS coil winding and figure 1c is a cross-section of a single
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`magnetic stimulation coil winding.
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`30
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`Figure 2a-e are schematic representations of the magnetic simulation coil winding as
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`presented in figures la and ¢ with varying sized and shaped ferromagnetic disks placed on
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`the rearward side of the coil winding.
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`WO 2017/187184
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`9.
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`Figure 3a and b are schematic representations of finite element modelled magnetic field
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`contour lines around the magnetic stimulation coil winding shownin figure la and the
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`magnetic stimulation coil winding as shownin figure 1d for comparative purposes.
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`S44
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`Figure 4 is an illustration of the finite element modelled magnetic field contour lines
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`produced by increase of the thickness of the ferromagnetic material.
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`Figures 5a and b are a comparison ofthe finite element modelled magnetic field contour
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`10
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`lines for a 16mm disk of ferromagnetic material in comparison to the same disk having
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`additional formations.
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`Figure 6 is a graphical representation of the magnetic field pulse wave forms from finite
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`element modelling as recorded beneaththe turns of MS coil winding of the distortion
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`15
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`arrangements as presented in figures 2a-e respectively.
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`Figure 7 is a representation of an exemplary embodiment of the present invention where
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`figure 7a is a representation of the patients side of a double coil winding, figure 7b is the
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`representation of the rearward or non-patient side of a magnetic simulation coil
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`20
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`arrangement including a distortion arrangement according to an exemplary embodiment of
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`the present invention and figure 7c is a schematic representation of a distortion
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`arrangement according to an exemplary embodiment.
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`Figure 8 is a graphical representation of the measured magnetic field on the forward or
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`25
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`patient side of the magnetic stimulation coil windings for the exemplary embodiment as
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`shownin figure 7.
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`Figure 9a-d are exemplary embodiments of ferromagnetic components for distortion
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`arrangements according to an exemplary embodiment.
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`30
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`Figure 10 is a schematic representation of further ferromagnetic components for use in
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`distortion arrangements according to an exemplary embodiment.
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`-10-
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`Referring to Figure 7a the forward side of the magnetic stimulation coil arrangementis
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`represented for presenting to a patient. Represented is a double coil winding made up of
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`two windings (3) covered to ensure generated heat does not transfer to the patient. At the
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`Ai
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`rearward side as presented in Figure 7b is a distortion arrangement (30) secured to the
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`magnetic stimulation coil windings (3). As better presented in Figure 7c, the distortion
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`arrangement comprises a plurality of ferromagnetic components (32), shownin a carrier
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`material (34). The carrier material (34) acts to both increase the external field strength for
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`which the ferromagnetic component array saturates (due to the gaps) and dampens noise
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`10
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`from the distortion arrangement. In the embodiment presented the ferromagnetic
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`components (32) are encapsulated in the carrier material (34).
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`In the exemplary
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`embodiment a hexagonalarray of 3mm ferromagnetic ball bearings have been providedin
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`an array stacked two layers high. The ball bearings are separated by the carrier material
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`(34) comprising a carrier resin and are held in place in a tray (36) which defines the outer
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`15
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`peripheral edge and also defines the apertures (9) in the distortion arrangement(30).
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`In
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`this exemplary embodiment apertures (9) are presented and are aligned with the
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`corresponding apertures in the middle of the magnetic stimulation coil windings (3). It
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`will be appreciated, however, that the distortion arrangement (30) may be configured to
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`cover these apertures and even more beneficially project into the apertures for increased
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`20
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`efficiency at the forward side of the MS coil arrangement.
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`It should be noted that in the exemplary embodimentthe ferromagnetic components (32)
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`are shownas spheres or ball bearings embeddedin the carrier (34). However alternative
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`shapes of ferromagnetic components maybe utilised such as discs for example shown in
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`25
`
`Figure 9 square, hexagons, triangle or any other shape. It will also be appreciated that
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`uregular shapes may be utilised as shown in Figure 10, howeverfor consistency of
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`operation the ferromagnetic components (32) are preferably of consistent shape. The
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`maximum dimension of the ferromagnetic components is preferably less than 2cm or 1/5
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`the diameter of the MS coil, and is preferably in the range of 0.045cm to lem. Suchsize of
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`30
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`ferromagnetic components combined with the carrier (34) provides a distortion
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`arrangementthat can withstand a higher applicd magnetic ficld strength before the
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`WO 2017/187184
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`-l]-
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`magnetic flux density in the distortion arrangement causes the distortion arrangement to
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`reach saturation point.
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`Referring now to Figure 8 there is a graphical representation of the magnetic field output
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`Ai
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`over time associated with a coil with no distortion arrangement measured adjacent the
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`forward side (as presented in curve 22) and the same measurementovertime associated
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`with a coil with the distortion arrangement comprising two full layers of ball bearings (32)
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`and a partially filled layer positioned the rearward side (as presented in curve 24). The
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`graph clearly shows the increase in maximum magnetic field output associated with the
`
`10
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`coil with the distortion arrangement positioned adjacent the forward side. As the number
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`of layer of ferromagnetic components increases so does the enhancementof the field.
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`A further important feature of the graph presented in Figure 8 is the difference in time
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`period associated with operation of the coil with and without a distortion arrangement. As
`
`15
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`described above,it is important that the distortion arrangementsaturates at a magnetic field
`
`strength typically associated with the use of magnetic stimulation coils, and particularly
`
`transcranial magnetic stimulation coils (TMS coils). For this reason it is important that the
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`distortion arrangement doesnot saturate at high applied magnetic fields. This can be
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`checked as follows. The inductance of the coil windings (3) can be measured both with
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`20
`
`and without the distortion arrangement presentat a low field strength knownto be well
`
`below the saturation level. This measurement shows that the inductance of the coil
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`increases by approximately 0.8microH. There is also an associated changein the time
`
`period. Thus, if the distortion arrangementis not saturating at a higher applied field, then
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`the time period will be expected to be the same,as if the distortion arrangement was
`
`25
`
`saturating the time period maybe different to the expected change from the increased
`
`inductance and showsigns of distortion from an attenuated sine wave. The reason forthis
`
`is that in the event of saturation of the distortion arrangement, the distortion arrangement
`
`will stop acting as a ferromagnetic material. The distortion arrangement according to the
`
`present invention has been shownto maintain ferromagnetic properties and thus not
`
`30
`
`saturate for a typical MS coil arrangement operated at full power. In addition the
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`waveformsare clearly not distorted from the expected attenuated sinc waveform which
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`also suggests the ferromagnetic material is not being saturated.
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`WO 2017/187184
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`PCT/GB2017/051190
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`-12-
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`An advantage associated with the provision of the array of ferromagnetic components
`
`embedded or encapsulated within the carrier (34) is the lower temperature rise during
`
`Operation in comparisonto a solid ferromagnetic plate. This is achieved through the
`
`fi
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`relative spacing between the ferromagnetic components (32) in the carrier 3(4). The
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`reduction in temperature rise within the distortion arrangementis achieved due to eddy
`
`currents being limited to only being induced within each ferromagnetic component(32)
`
`rather than through the distortion arrangement as a whole. As such, the carrier material
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`between each ferromagnetic component (32) acts to break up and hence minimise the eddy
`
`10
`
`currents.
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`It is also noted that extending the distortion arrangementinto the centres of the coil
`
`windings and aroundthe periphery of the coil windings may also be advantageous. Thisis
`
`shown in figure 2e and also enhancesthefield.
`
`15
`
`The present invention may be manufactured with relative ease. The ferromagnetic
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`components may be pressed into an insulating polymeric carrier material 14, which is
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`typically polymeric but may also be for example ceramic. A high thermally conducting
`
`potting compound maybe usedasthe carrier material to carry heat away from the coils in
`
`20
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`addition to its other functions. The ferromagnetic components may be mixed into a fluidic
`
`carrier material which subsequently solidifies to form a flexible or rigid body. The
`
`ferromagnetic components are then dispersed in a carrier material matrix.
`
`The present invention may be implemented into a non-planar distortion arrangement. This
`
`25
`
`meansthat the distortion arrangement can be formed to accommodate the contours of a
`
`selected coil. For example, in a figure of eight coil comprising first and second coils each
`
`of the coils maybetilted relative to the other coil. A distortion arrangement may therefore
`
`be formed with relative ease to accommodate such a configuration due to the ease of
`
`working with ferromagnetic components having a maximum dimension of between 0.1 and
`
`30
`
`3cm, and preferably in the range 0.1 to lem, and even more preferably in the range
`
`between 0.4 and lem. Such scale of ferromagnetic components lend themsclves to being
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`WO 2017/187184
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`PCT/GB2017/051190
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`moulded with a carrier material. The carrier material may comprise a potting compound,
`
`flexible rubber or other suitable non-metallic material.
`
`-13-
`
`The shape of the carrier material may be adjusted dependent upon the coil to be used. The
`
`A
`
`shape preferably generally matches the shape ofthe coil.
`
`Referring to Figures 9a to 9d alternative configurations of the ferromagnetic components in
`
`the distortion arrangement (30) are presented. In figure 9a layers of ferromagnetic
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`components (32) are presented spaced apart for clarity purposes and in Figure 9b as show
`
`10
`
`in a tightly packed array of five layers deep presented as an exemplary embodimentonly as
`
`ball bearings in a hexagonal array. Figure 9c is a presentation of ferromagnetic
`
`components in the form of ferromagnetic disks (32) and Figure 9d presents ferromagnetic
`
`disks (32) two layers deep. It will be appreciated that in any embodimentthe
`
`ferromagnetic components (32) are embedded, encapsulated or otherwise retained in a
`
`15
`
`carrier material.
`
`Theefficacy of different shapes of ferromagnetic components (32) has been tested, and it
`
`has been found that shapes other than spherical achieve similar effects provided with the
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`carrier material (34). For example, a distortion arrangement comprising a plurality of steel
`
`20
`
`bolts as shownin Figure 10 potted in a thermosetting plastic or silicone rubber gel as the
`
`carrier (32) achieves saturation at a higher applied magnetic field.
`
`In an embodiment according to another aspect of the invention it is possible to use, for
`
`example,iron filings or iron particles as a ferromagnetic material. However, the
`
`25
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`effectiveness of noise reduction must still be achieved and as such there must be sufficient
`
`quantity of carrier material in order to accommodateorattenuate the noise generated. For
`
`this reason the ratio of the volume of ferromagnetic particles to carrier material is less than
`
`1.5:1, preferably less than 1:1.
`
`30
`
`Again, the particles can be mixed into a fluid carrier which is subsequently poured into a
`
`mould and solidified to form the distortion arrangement(30).
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`WO 2017/187184
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`PCT/GB2017/051190
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`-14-
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`Aspects of the present invention enable enhancement of the magnetic field on the patient or
`
`forward side of the coil when placed on or adjacent to the rearward side. The increase in
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`magn