WO2001069278A1 - Active acoustic control in gradient coil design for mri - Google Patents
Active acoustic control in gradient coil design for mri Download PDFInfo
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- WO2001069278A1 WO2001069278A1 PCT/GB2001/001150 GB0101150W WO0169278A1 WO 2001069278 A1 WO2001069278 A1 WO 2001069278A1 GB 0101150 W GB0101150 W GB 0101150W WO 0169278 A1 WO0169278 A1 WO 0169278A1
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- coil
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3854—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
Definitions
- the present application relates to acoustically quiet gradient coil design in magnetic resonance imaging (MRI).
- Each sector consists of a split plate arrangement in which are embedded two windings, an outer primary winding and a narrow inner re-entrant loop control winding immediately adjacent to and surrounding the split or air gap.
- the wire spacing of the control winding is made small so as not to affect substantially the magnetic field created by the primary winding.
- transverse response expressions are derived from particular frequencies based on normal mode expansions for the plate.
- New detailed expressions are derived for the amplitude ratio of acoustic output in the additive and cancellation modes. This in turn has led to a novel plate design and to wire layout modifications which bring about acoustic cancellation along both plate axes.
- a method of producing an acoustically quiet coil design comprising first inner and outer surface conductor portions on a first block of material and second inner and outer surface conductor portions on a second block of material and including forming said portions of said each of said inner and outer surface conductor portions to be substantially completely rigid and connecting said inner surface conductor portion of said first block to said inner surface conductor portion of said second block and said outer surface conductor portion of said first block to said outer surface conductor portion of said second block by columns, struts or ties to form a substantially rigid structure.
- the present invention also provides an acoustically quiet coil design for MRI including a magnetic coil system comprising a first outer coil loop carrying a first current and a second inner coil loop carrying a second current at least a first portion of the first outer coil loop and a portion of the second inner coil loop being embedded in or fixed to a first block of first material of generally rectangular or arcuate shape with predetermined acoustic characteristics and at least a second portion of the first outer coil loop and a second portion of the second inner coil loop being embedded in or fixed to a second block of said first material generally of rectangular or arcuate shape with predetermined acoustic characteristics, said first and second blocks of material being separated by a second material which could be air and in which said first and second coils comprise a generally rectangular or arcuate path and in which at least the second portion of said inner coil is positioned to create a force when energized with said first and second currents appropriately phased either to counter or to assist the force generated by said first portion of said outer coil on at least two opposite sides of each of
- the present invention also provides a method of providing an acoustically quiet coil design for MRI including a magnetic coil system consisting of at least four sectors each sector comprising a first outer coil loop carrying a first current and a second inner coil loop carrying a second current at least a first portion of the first outer coil loop and a first portion of the second inner coil loop being embedded in or fixed to a first block of first material of generally rectangular or arcuate shape with predetermined acoustic characteristics and at least a second portion of the first outer coil loop and a second portion of the second inner coil loop being embedded in or fixed to a second block of said first material generally of rectangular or arcuate shape with predetermined acoustic characteristics, said first and second blocks of material being separated by a second material which could be air and in which said first and second coils comprise a generally rectangular or arcuate path and in which at least the second portion of said inner coil is positioned to create a force when energized with said first and second currents appropriately phased either to counter or assist the force generated by said first
- the wave propagation at a distance x within the first material is described by
- Fig. 1 is a sketch of a flat rectangular wire loop of width 2d and length £ carrying a current I.
- the loop is embedded in a block of material of width 2D and length L with the loop plane normal to the magnetic field B. Sound S is emitted along the z-axis;
- Fig. 3 shows (a) Graph of acoustic response data Ss A p s '°(dB) versus x for the arrangement of Fig. 2.
- the solid curves are the fitted theoretical expressions, Eq.[7].
- the plate material was GRE 10G 40 (Tufhol);
- the solid curves are the theoretical expressions, Eq.(l l). The plate material is 12 mm thick cast polyester/styrene sheet; (b) Graph of acoustic response data as is Fig. 4(a) above. The solid curves are the improved theoretical expressions based on the normal mode theory and
- the first version P,P' shows the inner loop extended to cover the ends P' producing cancellation or addition along the y-axis as well as normal operation along the x-axis.
- Each plate may comprise a flat rectangular plate or an arcuate shaped rectangular plate.
- the arrangement Q,Q' substitutes for P,P' and again produces either cancellation or addition along the y-axis but in a symmetric manner which balances Lorentz forces along the y-axis;
- Fig. 6 is a diagram showing the strut/tie assembly of supporting columns within the split plate assembly.
- the columns are glued within the plate material and touch the outward current, Ij, conductor at one end and the return current, I 2 , conductor in both halves of the plate assembly.
- the coupling of the rods to the inner loop conductor may include a small pad which also acts as a load spreader. This leads to an inter-digitation effect.
- the rods or columns may also be potted within the plate assembly;
- Fig. 7 is a sketch of an alternative arrangement for the inter-digitated strut/tie assembly.
- each half of the plate assembly is made from a low acoustic velocity plastic material, the long edges of which are capped with a thin strip of a much stiffer material.
- the inter-digitated rods pass through the plastic body of the plate and are fixed at each end in the capping strips as shown. In one embodiment, the rods do not touch the plate material but pass through the body of the plate and through one edge capping to make contact with the edge cap of the second half of the plate assembly immediately adjacent to the gap.
- rods are either cemented to the body of the plate or are potted into the plate when it is cast;
- Fig. 8 is a diagram of a four sector gradient coil for generation of either an x-,y- or a z-gradient.
- Each sector comprises a split plate coil as in Fig. 2.
- the inner coil or control winding of each sector carries a current I 2 e' ⁇ and forms a re-entrant loop within the primary winding which carries a current Ij.
- NB the sector spacing for a z-gradient will in general be different to that for an x- or y-gradient.
- Figs. (9a- f) shows a number of plate edge stiffening arrangements in which either the conductor itself is shaped or the edge is stiffened with aligned fibre composites and on which the conductor is added.
- v s is the compressional wave velocity in the solid.
- the use of rectangular plates makes the theory of wave propagation within the solid plate much easier to handle.
- the plates themselves are fabricated from suitable reinforced plastic laminates such that the wave propagation velocity within the material is high, typically around 2.5 kms "1 .
- the materials have very low losses and these factors simplify the theoretical approach.
- phase changes associated with displacements can be ignored.
- I l5 which is the outer loop current
- ⁇ e 10 which is the inner loop current applied with a phase ⁇ relative to l ⁇ . Ignoring constant phase shift terms the acoustic output amplitude from the face of the plate structure, after some algebra, is given by
- variable, s, used in Eqs. [6] and [9] is the displacement of the plate centres from the plate assembly origin, as indicated in Fig. 2.
- a S S P ( ⁇ 0)
- F is the Lorentz force applied by the wire at the plate edges
- d is the width of the plate
- A is the cross-sectional area of the plate edge
- E is Young's Modulus.
- a e is the vibrational amplitude due to elastic displacements and the enhancement factor is
- a (k, x) 2 k — cos(k ⁇ V 2) sin( v ⁇ x d), [21 ] d and redefined along the y-axis as
- ⁇ sm( ⁇ yl£) ⁇ A?(k,y)/(/ 2 ⁇ l ⁇ ⁇ 2 ) [22]
- Equations [21] and [23] are the spatial parts of the general solution of Eqs.[18]
- K ⁇ e ⁇ .
- Equations [33] and [34] may be written in matrix form as
- ⁇ g h are the eigenvalues which represent the collective modes of vibration in two dimensions.
- Eqs. [14] and [15] H(k,D,L) is derived from the two-dimensional Fourier components of the k- wave analysis. If the free vibration normal modes along the x- and y-axes are ⁇ g/D and ⁇ h/L respectively, where g and h are integers, the combined collective mode frequencies become
- Q,Q' substitutes for P,P' and again produces either cancellation or addition along the x-axis.
- the actual displacement of the plate can be calculated knowing the force, its time dependance, and the mass of the plate. This we have done to produce the result of Eq.[16].
- the opposing force ideally should be applied in a distributed form throughout the body of the plate. This may be possible by reinforcing the plate appropriately with extremely strong columns of material such that opposing forces applied to the ends of the columns will be transmitted as rapidly as possible throughout the plate material.
- each half-plate the Lorentz forces, F, within each half-plate are equal and opposite, thus squeezing the plate material and thereby launching the wave excitation within the plate described by Eq. [12].
- the motion of each half- plate is symmetric about its centre.
- the wave within the plate is described by a rapidly convergent normal mode expansion which may be approximated by the leading term, a-..
- the ratio, R, of reduced/full acoustic output may, therefore, be approximated by
- the materials that might form the columns in the above described arrangement could be ceramics like Corundum (A1 2 0 3 ), Zirconium Oxide, Silicon Nitride, Silicon Carbide, Tungsten Carbide or carbon fibre reinforced epoxy (CRE) rods.
- CRE carbon fibre reinforced epoxy
- the typical velocity of sound is in excess of 9 kms "1 .
- high sound velocities may be expected for aligned carbon fibre rods.
- Somewhat lower but useful velocities may be expected for aligned glass fibre rods set in epoxy, also known as GRE pultrusions.
- GRE carbon fibre reinforced epoxy
- the rods or columns could approximate well to near instantaneous delivery of the opposing Lorentz forces throughout the body of the plate.
- the physical arrangement visualised corresponds to an inter-digitated strut/tie assembly as shown in Fig. 6.
- the advantage of this arrangement is that in cancellation mode the relevant wires are effectively coupled together through the rods or columns by the shortest route that ensures that all rods are the same length.
- the plate material is drilled to take the columns which are stuck in and which physically touch the wires.
- the coupling of the rods to the inner loop conductor may include a small pad which also acts as a load spreader.
- the rods or columns may also be moulded, cast or potted into the plastic plate assembly.
- the columns of ceramic material pass through the body of the plates but in one embodiment do not touch the plates.
- the plates have edge caps made of a much stronger and stiffer material, possibly GRE 10G/40 or CRE, which serve to spread the loads and the ceramic columns are arranged to make contact with the edge caps which support the plate wires as shown.
- GRE 10G/40 or CRE a much stronger and stiffer material
- the outer conductor carrying current, I l s and the inner conductor carrying current, I 2 e 10 are either embedded in or fastened to or glued to the edge capping material.
- further modifications along the lines described in Fig. 5 may be additionally introduced in order to quench vibration along the y-axis.
- the advantage of the arrangement of Fig. 7 is that propagation times within the columns are equal, the plate assembly operates correctly in the switched mode giving very large outputs in the additive mode and very low outputs in the cancellation mode.
- the ceramic rods may be glued into the plates, thereby transmitting the cancellation force uniformly through the body of the plate.
- An alternative to gluing into machined holes is to cast the plastic resin into sheet form with the rods in situ. This would reduce fabrication costs.
- Residual unwanted acoustic radiation from the plate edges may be reduced by the methods described in the prior art (P. Mansfield, UK Patent Application, 9920185 1999).
- FIG. 8 A typical four sector arrangement of plate-pairs is shown in Fig. 8 and can be used to produce an x-, y- or a z-gradient. It is emphasised that gradient coils can be generated from the basic arrangement of Fig. 8 using multi- plate stacks to generate all three orthogonal axes, G x , G y and G z , thereby improving gradient linearity. Stacking plates may affect the overall acoustic efficacy of the gradient coils. If sound levels increase additional sound absorbing material may be interleaved between the plates (P. Mansfield, US Patent, 5, 990, 680 November 23 1999, Priority Date 1 April 1995).
- FIG. 9a- f shows a number of plate edge stiffening arrangements in which either the conductor itself is shaped or the edge is stiffened with aligned fibre composites and on which the conductor is added.
- the fibre composites could include epoxy single glass fibre bundles running the length of the plate edge or epoxy single carbon fibre bundles.
- Figs. (9c-f) show the conductor as a flat strip mounted on the aligned fibre composite edge stiffener, it would clearly be possible to shape the conductor in the form of a U-section or other section to give additional stiffening. If the conductors alone form the edge stiffening as in fig. 9(a), then the rods would be fixed, screwed or cemented directly into the conductor stiffening edges. Otherwise the rods would be fixed, screwed or cemented into the aligned fibre composite material. The rod spacing as indicated in Figs.
- edge stiffeners Similar arguments apply to the edge stiffeners. To maintain the integrity of the plate assembly and electrical continuity flexible copper braid can be used where appropriate and a softer flexible material can be used to join the plate sections where necessary. Adding in soft flexible material, will, of course, produce low frequency Chladni resonances but the object here would be to create clear resonant mode windows in which the compressional response behaviour of the plate can operate in an unhindered and unperturbed manner.
- o:F F' is a measure of the effective force applied at the plate edges due to the presence of the rods.
- the factor a will in general lie in the range O ⁇ ⁇ ⁇ l and will depend on the applied frequency, the elastic properties of the rods as well as the plate and rod dimensions.
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/221,935 US7030610B2 (en) | 2000-03-17 | 2001-03-16 | Active acoustic control with flexible joints in gradient coil design for MRI |
AU40858/01A AU4085801A (en) | 2000-03-17 | 2001-03-16 | Active acoustic control in gradient coil design for mri |
JP2001568103A JP3677003B2 (en) | 2000-03-17 | 2001-03-16 | Active acoustic control method in MRI gradient coil system |
EP01911937A EP1269210B1 (en) | 2000-03-17 | 2001-03-16 | Active acoustic control in gradient coil design for mri |
AT01911937T ATE456060T1 (en) | 2000-03-17 | 2001-03-16 | ACTIVE ACOUSTIC CONTROL IN DESIGNING GRADIENT COILS FOR MAGNETIC RESONANCE IMAGING |
DE60141125T DE60141125D1 (en) | 2000-03-17 | 2001-03-16 | ACTIVE ACOUSTIC CONTROL IN THE DESIGN OF GRADIENT COILS FOR THE IMAGING MAGNETIC RESONANCE |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB0006356.0 | 2000-03-17 | ||
GBGB0006356.0A GB0006356D0 (en) | 2000-03-17 | 2000-03-17 | Active acoustic control in gradient coil design for MRI |
Publications (1)
Publication Number | Publication Date |
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WO2001069278A1 true WO2001069278A1 (en) | 2001-09-20 |
Family
ID=9887747
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB2001/001150 WO2001069278A1 (en) | 2000-03-17 | 2001-03-16 | Active acoustic control in gradient coil design for mri |
Country Status (9)
Country | Link |
---|---|
US (1) | US7030610B2 (en) |
EP (1) | EP1269210B1 (en) |
JP (1) | JP3677003B2 (en) |
CN (1) | CN1268936C (en) |
AT (1) | ATE456060T1 (en) |
AU (1) | AU4085801A (en) |
DE (1) | DE60141125D1 (en) |
GB (1) | GB0006356D0 (en) |
WO (1) | WO2001069278A1 (en) |
Families Citing this family (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB0006356D0 (en) * | 2000-03-17 | 2000-05-03 | Mansfield Peter | Active acoustic control in gradient coil design for MRI |
DE10253701B4 (en) * | 2002-11-18 | 2005-12-08 | Siemens Ag | Potted RF components, encapsulated gradient coil for Magnetic Resonance Imaging Scanner, with actuators for active noise abatement, as well as methods for their manufacture and apparatus for carrying out the method |
GB2419416A (en) * | 2004-10-20 | 2006-04-26 | Gen Electric | Method of manufacturing gradient coil for MRI device |
DE102005058651B4 (en) * | 2005-01-26 | 2012-02-16 | Siemens Ag | Magnetic resonance device and integrated gradient and radio frequency coil unit |
DE102005030745B4 (en) * | 2005-06-29 | 2008-05-29 | Schleifring Und Apparatebau Gmbh | RF coils for magnetic resonance imaging |
US7554326B2 (en) * | 2006-05-17 | 2009-06-30 | Kabushiki Kaisha Toshiba | MRI gradient magnetic coil unit assembley using different resins within windings and between components |
JP4402707B2 (en) * | 2007-07-06 | 2010-01-20 | 三菱電機株式会社 | Shim support guide jig for magnetic field generator |
GB2483890A (en) * | 2010-09-22 | 2012-03-28 | Tesla Engineering Ltd | MRIS gradient coil assembly with screening layers connected to respective coil layers |
US8890529B2 (en) * | 2011-05-31 | 2014-11-18 | General Electric Company | System and apparatus for providing interconnections in a gradient coil assembly |
US8766635B2 (en) | 2011-06-30 | 2014-07-01 | General Electric Company | System and apparatus for balancing radial forces in a gradient coil |
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US5764059A (en) * | 1993-06-02 | 1998-06-09 | British Technology Group Limited | Acoustic screen |
US5990680A (en) * | 1995-04-01 | 1999-11-23 | Mansfield; Peter | Active acoustic control in quiet gradient coil design for MRI |
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US5276398A (en) * | 1992-06-01 | 1994-01-04 | Conductus, Inc. | Superconducting magnetic resonance probe coil |
US5351007A (en) * | 1992-06-01 | 1994-09-27 | Conductus, Inc. | Superconducting magnetic resonance probe coil |
US5594342A (en) * | 1992-06-01 | 1997-01-14 | Conductus, Inc. | Nuclear magnetic resonance probe coil with enhanced current-carrying capability |
US5585723A (en) * | 1995-03-23 | 1996-12-17 | Conductus, Inc. | Inductively coupled superconducting coil assembly |
US5565778A (en) * | 1992-06-01 | 1996-10-15 | Conductus, Inc. | Nuclear magnetic resonance probe coil |
EP0774670B1 (en) * | 1995-11-16 | 2002-05-02 | Siemens Aktiengesellschaft | Magnet assembly for a diagnostic magnetic resonance apparatus |
GB9620138D0 (en) * | 1996-09-27 | 1996-11-13 | Mansfield Peter | Active control of acoustic output in gradient coils |
GB9804829D0 (en) * | 1998-03-07 | 1998-04-29 | Mansfield Peter | Improvements in active acoustic control |
US6456074B1 (en) * | 2000-01-28 | 2002-09-24 | Intermagnetics General Corporation | Quiet gradient coil |
GB0006356D0 (en) * | 2000-03-17 | 2000-05-03 | Mansfield Peter | Active acoustic control in gradient coil design for MRI |
US6771070B2 (en) * | 2001-03-30 | 2004-08-03 | Johns Hopkins University | Apparatus for magnetic resonance imaging having a planar strip array antenna including systems and methods related thereto |
US7091721B2 (en) * | 2001-04-18 | 2006-08-15 | IGC—Medical Advances, Inc. | Phased array local coil for MRI imaging having non-overlapping regions of sensitivity |
US6661229B2 (en) * | 2001-04-30 | 2003-12-09 | Ge Medical Systems Global Technology Company, Llc | RF birdcage coil with reduced acoustic noise |
-
2000
- 2000-03-17 GB GBGB0006356.0A patent/GB0006356D0/en not_active Ceased
-
2001
- 2001-03-16 EP EP01911937A patent/EP1269210B1/en not_active Expired - Lifetime
- 2001-03-16 US US10/221,935 patent/US7030610B2/en not_active Expired - Fee Related
- 2001-03-16 AT AT01911937T patent/ATE456060T1/en not_active IP Right Cessation
- 2001-03-16 WO PCT/GB2001/001150 patent/WO2001069278A1/en active Application Filing
- 2001-03-16 JP JP2001568103A patent/JP3677003B2/en not_active Expired - Fee Related
- 2001-03-16 AU AU40858/01A patent/AU4085801A/en not_active Abandoned
- 2001-03-16 DE DE60141125T patent/DE60141125D1/en not_active Expired - Fee Related
- 2001-03-16 CN CN01808520.2A patent/CN1268936C/en not_active Expired - Fee Related
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US5764059A (en) * | 1993-06-02 | 1998-06-09 | British Technology Group Limited | Acoustic screen |
US5990680A (en) * | 1995-04-01 | 1999-11-23 | Mansfield; Peter | Active acoustic control in quiet gradient coil design for MRI |
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Title |
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MANSFIELD P ET AL: "SOUND GENERATION IN GRADIENT COIL STRUCTURES FOR MRI", MAGNETIC RESONANCE IN MEDICINE,US,ACADEMIC PRESS, DULUTH, MN, vol. 39, no. 4, 1 April 1998 (1998-04-01), pages 539 - 550, XP000740834, ISSN: 0740-3194 * |
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US20030155174A1 (en) | 2003-08-21 |
ATE456060T1 (en) | 2010-02-15 |
EP1269210A1 (en) | 2003-01-02 |
AU4085801A (en) | 2001-09-24 |
US7030610B2 (en) | 2006-04-18 |
JP2003527177A (en) | 2003-09-16 |
DE60141125D1 (en) | 2010-03-11 |
EP1269210B1 (en) | 2010-01-20 |
CN1426538A (en) | 2003-06-25 |
JP3677003B2 (en) | 2005-07-27 |
GB0006356D0 (en) | 2000-05-03 |
CN1268936C (en) | 2006-08-09 |
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