method to homogenize a magnetic field, detector to detect magnetic resonance and panel to homogenize

专利摘要:
METHOD AND APPARATUS TO PRODUCE HOMOGENEOUS MAGNETIC FIELDS A method for chocking a magnetic field is revealed using a single chock chain to contribute to the suppression of more than one geometric component of an inhomogeneity in the magnetic field without changing the geometry of the chock path. apparatus for implementing the method is also revealed. In the modalities, the devices comprise chock paths substantially oriented in a common way.
公开号:BR112012013588B1
申请号:R112012013588-0
申请日:2010-12-01
公开日:2021-01-26
发明作者:Garett M. Leskowitz；Gregory McFEETORS；Sebastien PERNECKER
申请人:Nanalysis Corp.；
IPC主号:

专利说明:

[0001] The present invention relates to the suppression of inhomogeneity in magnetic fields Background
[0002] Relevant foundation publications include the following: McDowell, A. and Fukushima, E., "Ultracompact NMR: 1H Spectroscopy in a Subkilogram Magnet", Applied Magnetic Resonance 35 (1), 185-195, 2008. This reference demonstrates NMR spectroscopy on a compact permanent magnet with nanoliter samples -volume.
[0003] Blümich, Bernhard, et al., "Mobile NMR for Geophysical Analysis and Materials Testing", Petroleum Science 6 (1), 1-7, 2009. This reference shows a compact NMR spectrometer that employs a Halbach magnet model.
[0004] Chmurny, Gwendolyn N. and Hoult, David I., "The Ancient and Honorable Art of Shimming", Concepts in Magnetic Resonance Part A 2 (3), 131-149, 2005. This reference details the use of harmonic function expansions spherical in paving.
[0005] Raich, H. and Blumler, P., "Design and Construction of a Dipolar Halbach Array with a Homogeneous Field from Identical Bar Magnets: NMR Mandhalas", Concepts in Magnetic Resonance B: Magnetic Resonance Engineering 23B (1), 16-25, 2004. This reference details the use of Halbach-type magnets made from cubic magnets in nuclear magnetic resonance spectrometers.
[0006] Moresi, Giorgio and Magin, Richard, "Miniature Permanent Magnet for Table-top NMR", Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering 19B (1). 35-43, 2003. This reference reveals efforts to make the field within Halbach's arrangements more homogeneous for NMR applications using flat polar parts. She also mentions a crested design configuration.
[0007] Danieli, Ernesto, "Mobile Sensor for High Resolution NMR Spectroscopy and Imaging", Journal of Magnetic Resonance 198, 80-87, 2009. This reference reveals efforts to make the field more homogeneous using magnets placed within a primary Halbach array.
[0008] Keim, Thomas A., "Intentionally Non-orthogonal Correction Coils for High-homogeneity Magnets", United States Patent No. 4,581,580, 1986. Reveals the use of a set of shim coils capable of producing multiple spherical harmonics through variation of the specified set of applied currents. A given coil within the set can contribute to more than a single spherical harmonic function.
[0009] Golay, MJE, "Homogenizing Coils for NMR Apparatus", United States Patent 3,622,869, 1971. Reveals the use of homogenization coils to optimize the magnetic fields that consist of electrical conductors affixed to the electrically insulating plates and placed parallel and adjacent to the magnetic polar parts.
[0010] Kabler, Donald J., Gang, Robert E., and Reeser, Jr., William O., "Magnetic Field Shim Coil Structure Using Laminated Printed Circuit Sheets", United States Patent No. 3,735,306, 1973. Reveals coils of field homogenization built with printed circuit sheets placed parallel and adjacent to the polar parts in a separate module.
[0011] United States Patent 4,682,111, 1987, to Hughes, discloses the use of molded polar parts to improve the homogeneity of the static magnetic field.
[0012] Rose N.E., "Magnetic Field Correction in the Cyclotron", Phys. Rev. 53, 715-719, 1938. Describes polar pieces with ridges for use in the homogenization of magnetic fields in cyclotrons.
[0013] O'Donnell, Matthew, et al., "Method for Homogenizing a Static Magnetic Field Over an Arbitrary Volume", United States Patent No. 4,680,551, (issued July 14) 1987. Reveals the selection of paving chains based on magnetic field mapping and a weighted least squares calculation.
[0014] US 3,735,306 describes a shimming coil structure (homogenization of the magnetic field) that uses laminated printed circuit sheets. US 6,002,255 discloses an open planar magnet MRI system having active target field shimming. Document US2001 / 0050176 A1 discloses an electrical conductor device that has conductive loops that are arranged in areas with limiting lines defined by a network structure and in which the control devices are connected for the control of currents within the conductor device . Document US 3,622,869 describes a nuclear magnetic resonance apparatus adapted to homogenize a field.
[0015] In a nuclear magnetic resonance (NMR) experiment, a sample is placed under the influence of a static polarizing magnetic field, which partially aligns the sample's nuclear spin magnetic moments. The precession of moments occurs in the static field at a frequency, called the Larmor frequency, which is proportional to the intensity of the field. The sample's magnetic moments can be manipulated by applying a transverse radiofrequency (RF) magnetic field at the Larmor frequency. By observing the reaction of the sample to the RF field, it is possible to obtain an understanding of the analysis in the chemical composition of the sample. The ability of NMR as an analytical method can largely be a function of how well the characteristics of the applied magnetic fields can be controlled.
[0016] The practice of paving magnetic fields (making the fields more uniform) has existed since the early days of NMR and originally used thin pieces of metal physically placed behind the source magnets to adjust the positions of those magnets to refine the magnetic field. Most modern paving techniques use electromagnetic coils. Conventional magnetic resonance spectrometers commonly use shim coils arranged in substantially cylindrical coil shapes. The use of shim coils in compact NMR devices has proven to be difficult mainly due to space restrictions that may not accommodate traditional shim coil systems, which can have many layers. The space available within a main magnet in many such devices may be too small to accommodate a typical set of shim coils whose individual elements are individually designed predominantly to deal with one and only one geometric aspect or geometric component of the residual inhomogeneity of the main magnetic field.
[0017] Figures 1A, 1B and 1C compare the main polarization field and sample-tube configurations of typical high field spectrometer models with a model for compact magnet systems based on the Halback cylindrical arrangement. The arrows labeled B indicate the direction of the main magnetic field. No sidewalk measurement is shown in the figures. Figure 1A shows schematically the superconducting field coils of the high-field magnet, an inserted cylindrical sample tube, and the B field produced by the coils. The magnetic field within the sample volume is aligned along the common axis of symmetry of the coils and the tube.
[0018] Figures 1B and 1C show the same sample tube inserted in a cylindrical Halbach magnet arrangement, which produces a B field perpendicular to the tube's axis of symmetry. This specific Halbach arrangement is composed of eight magnets in a circular arrangement placed around the tube, with the magnetization vectors of the magnets (shown as arrows) perpendicular to the axis of symmetry of the tube. The field within the Halbach array is quite uniform for some applications, but it can be very inhomogeneous for some high resolution NMR experiments.
[0019] To substantially reduce the inhomogeneity of a magnetic field, it may be useful to have independent control over different geometric aspects of the inhomogeneity of the field. In many MRI applications, the main magnetic field is strongly polarized along a specified direction, which we consider to be the Z-axis of a Cartesian frame of reference whose origin is at a certain fixed point. The Larmor frequency of magnetic rotations located at a point in space is determined by the magnitude of the field at that point, which in reasonably homogeneous fields is very closely approximated by the Z-component of the field, Bz. You can expand Bz as a scaled sum of functions,
[0020] For example, commonly, an expansion in spherical harmonic functions is used, where the functions are fn, m (x, y, z) = Nn, mPn, m (cosθ) exp (imΦ) fn, m (x, y, z) = Pn, m (cosθ) exp (imΦ), Where
[0021] If, in addition, the product scaled between each function fk and itself is equal to 1, then the set of functions is said to be orthonormal. summary
[0022] Methods and apparatus for suppressing inhomogeneities in a magnetic field are revealed. The methods comprise the use of one or more paving paths, and a paving path can be used to chock more than one geometric component of the field without any change in the geometry or spatial location of the shimming path.
[0023] In a first modality, a method is revealed to wedge a magnetic field in which there is an inhomogeneity having more than one geometric component, the magnetic field being produced by a set of magnets, the method comprising: applying a plurality of modulated single wedge chains coordinated along corresponding paths of a plurality of substantially commonly oriented paving paths, a portion of each paving path located within the set of magnets; and suppressing more than one geometric component of inhomogeneity in the magnetic field using the plurality of paving currents.
[0024] In an alternative modality, the plurality of paving chains is arranged in a common plane.
[0025] In an alternative modality, individual paths of paving paths are substantially commonly oriented: they are substantially straight; or comprise two substantially straight portions separated by a sudden change of direction; or comprise three substantially straight portions separated by sudden changes in direction; or comprise a region that has a zigzag configuration.
[0026] In an alternative embodiment, a sample is inserted into the magnetic field along an axis and the orientation of the paving paths is substantially parallel to the axis.
[0027] In an alternative modality, each individual current of the plurality of paving currents flows in a respective path of the plurality of paving paths and in which the individual currents of the currents are determined by: estimating a magnetic field produced by the application of a current known to each one of several paving paths; computation of a scalar product of representative functions of the geometric components of the estimated magnetic field to obtain values of geometric components; arrangement of the values of geometric components in a matrix; determining a pseudo-inverse of the matrix to obtain pseudo-inverse matrix values; and choosing the individual currents among the currents according to the pseudo-inverse matrix values.
[0028] In an alternative mode, the application comprises adjusting the magnitudes of the curb currents in a coordinated way.
[0029] In an alternative embodiment, a single paving current induces an image current in a magnetically permeable material in the vicinity of the paving path.
[0030] In an alternative embodiment, a detector is revealed to detect magnetic resonance in a sample exposed to a main magnetic field, the detector comprising: a substantially flat pavement panel having two ends; and a plurality of paving paths having a substantially common orientation extending between the two ends, the paving paths for applying paving chains to them.
[0031] In an alternative embodiment, the detector comprises a longitudinal space that has an axis, the longitudinal space for inserting a sample probe containing the sample along the axis and in which the orientation is substantially parallel to the axis.
[0032] In an alternative embodiment, the flat pavement panel comprises two flat panels.
[0033] In an alternative modality, the detector comprises polar parts on which the two flat shimming panels are mounted, the polar parts extending within a longitudinal space.
[0034] In an alternative embodiment, one of the paving currents induces an image current within a polar part.
[0035] In an alternative modality, at least a subset of the various paving paths is arranged in substantially parallel planes.
[0036] In an alternative embodiment, a printed circuit board is provided in which the flat pavement panel is comprised.
[0037] In an alternative modality, the paving paths either: comprise substantially straight regions separated by a sudden change of direction; or they are substantially parallel across at least a portion of their lengths.
[0038] In an alternative embodiment, a paving panel is disclosed which has substantially spaced first and second ends and a substantially flat portion comprising a plurality of paving paths each extending substantially between the ends, wherein the paving paths: comprise substantially regions straight lines separated by a sudden change in the direction of the path; or they are substantially parallel across at least a portion of their length; or it has a substantially common orientation.
[0039] In alternative modes, the paving paths are on a common plane.
[0040] In alternative modalities the detector accepts the insertion of a sample along an axis and the ends of the panel are substantially oriented along the axis.
[0041] In alternative modalities, the pavement panel comprises a printed circuit board. In an alternative embodiment, a method is revealed to determine the curb currents for an MRI device, the method comprising the steps of: estimating the magnetic field produced by applying a known current to a number of curb paths; discover the geometric components of a magnetic field produced using a scalar product of functions; arrange the values obtained as geometric components in a matrix; and choose the applied currents according to the values in a pseudo-inverse of the matrix.
[0042] In the embodiments, an MRI device can be an NMR detector and can be an NMR spectrometer.
[0043] In the modalities, the curb currents are determined by estimating the effects of unit currents applied to the paths and the estimation can include: simulating a unit curb field; or map a unitary pavement field.
[0044] In the modalities, each individual stream flows in a path and the individual stream currents are determined by: discovering the scalar product of the geometric components of the unitary pavement fields for the paths; arrangement of products in a matrix; and choosing the currents as proportional to the values in a corresponding entry in a pseudo-inverse of the matrix.
[0045] In the modalities, a paving apparatus is revealed for paving a magnetic field having two geometric components, the apparatus comprising a paving path and characterized in that the apparatus is operable to suppress the inhomogeneities in different geometric components of the magnetic field by changing the magnitude of a current applied to the path while the path geometry remains constant.
[0046] Characteristics and advantages of the subject under study will become more evident in the light of the following detailed description of the selected modalities, as illustrated in the attached figures. As will be perceived, the material under study revealed and claimed is capable of modifications in several aspects, all without departing from the scope of the present material under study. Consequently, the drawings and description should be considered as illustrative, and not restrictive. Brief Description of Drawings
[0047] Figure 1A is a schematic side showing a sample tube in a coil arrangement to produce a strong magnetic field aligned along an axis of symmetry of the sample tube for NMR. Figure 1B is a schematic top view showing a sample tube in a cylindrical Halbach magnet arrangement seen along the tube's axis of symmetry. Figure 1C is a schematic perspective view showing a sample tube in a cylindrical Halbach magnet arrangement seen along an axis perpendicular to the symmetry axis of the tube. Figure 2A is a schematic top view of a space in which a modality of a pavement panel could be inserted or within which a modality of a pavement panel can be positioned. Figure 2B is a side view of a space according to Figure 2A. Figure 3 shows an end view of a set of magnets suitable for producing a magnetic field substantially along the z axis. Figure 4A shows a side view of a polar part model for use with a pavement panel according to a modality. Figure 4B is a view of a part and pole taken at right angles to Figure 4A. Figure 4C shows detail of Figure 4B. Figure 5 shows an arrangement of two pieces and pole with paving panels according to a modality. Figure 6 is a plan view showing a modality of a paving panel. Figure 7 is a plan view showing a second embodiment of a paving panel having a zigzag pattern of paving paths on each of the two sides or two layers of the panel. Figure 8 is a three-dimensional graph showing a magnetic field profile produced by applying a current of 200mA to one of the lines shown in Figure 7 in isolation. Figure 9 is a three-dimensional graph showing a magnetic field profile produced by applying currents to the lines of Figure 7 in combination. Figure 10 shows a block diagram of a first general modality. Figure 11A shows an alternative form of a paving panel. Figure 11B shows a first layer of the paving paths from the panel according to Figure 11A. Figure 11C shows a second layer of the paving paths from the panel according to Figure 11A. Figure 11D shows a third layer of the paving paths from the panel according to Figure 11A. Figure 11E shows the fourth layer of the paving paths from the panel according to Figure 11A. Figure 12 shows a section perpendicular to the array of magnets according to Figure 13. Figure 13 shows a block diagram of an example of a modality. Figure 14 shows a pavement panel according to an alternative modality. Detailed Description of Preferred Terms
[0048] In this disclosure, the recitation of a specified number of elements is understood to include the possibility of any greater number of such elements. Thus, for example, the recitation that a pavement panel comprises two pavement paths, indicates that the pavement panel comprises at least two pavement paths, but can comprise 3, 4, 5 or any number of larger pavement paths. than two. Similarly, reference to the individual elements of a group of elements indicates that any single element or more than one of such elements has the specified property or characteristic.
[0049] In this disclosure the term "paving" refers to any method for suppressing inhomogeneity of the magnetic field. The magnetic field can be a main magnetic field and can be generated or maintained within an MRI device; which can be an NMR machine, can be a spectrometer and can be a compact NME machine.
[0050] In this disclosure the term "magnetic resonance" or "MR" means resonant reorientation of a sample's magnetic moments in a magnetic field or fields; and includes nuclear magnetic resonance (NMR), electron spin resonance (SER), magnetic resonance imaging (MRI) and ferromagnetic resonance (FMR). As the present invention relates to methods and apparatus for making static magnetic fields in general more uniform, the invention can also be applied in ion cyclotron resonance (ICR). In specific applications and modalities the devices and methods revealed are applied to NMR and in modalities they are applied to NMR spectrometers or NMR image makers. Materials that exhibit magnetic resonance when exposed to a magnetic field are referred to as magnetically resonant or nuclides or active MR materials.
[0051] In this disclosure the terms "shimming", "path", "shimming path", "shimming trace", "current path" and the like refer to the current conduction paths to suppress inhomogeneity in a primary magnetic field. A "curb chain" is a chain applied to a shimming path. A "shimming field" or "paving field" refers to a magnetic field generated by one or more shimming paths or shimming currents. In the embodiments such paths can be supported on a suitable surface generally referred to as a "shimming plate" or "shimming panel" which can be a plate and can be substantially non-conductive or substantially non-magnetic. In the embodiments, a path can be directly supported by the surface of a primary magnet or the surface of a magnetically permeable material. In the specific modalities the paths can be provided in or on one, two, three, four, five or more layers, or planes on, or on, less than: six, five, four, three or two layers or plan of a panel of shimming, and a shimming panel can comprise or support any suitable number of shimming paths. In the specific modalities, the shimming panels can comprise or support 8 or 24 paths, but in the alternative modalities 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 , 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or more paths are possible. A panel may comprise substantially opposite or mutually spaced ends, and a path may have ends close to each of the two ends of the shimming panel. In the modalities, the shimming panels can be positioned parallel or perpendicular to a primary magnetic field or in any other desired orientation.
[0052] In the modalities of the shimming panels, the arrangement of the shimming paths in multiple layers or planes can allow a better and more accurate control of the pavement fields. In the modalities, the shimming panels can be printed circuit boards that can be ultrafine printed circuit boards with paths in the appropriate geometry. In alternative modalities, the construction of the shimming panels can use magnetically transparent materials such as low temperature fired ceramics ("LTCC"). A range of alternative materials will be readily apparent to those skilled in the art. The paths can be parallel or substantially parallel throughout their length. A path can reverse direction and can be curved or straight integrally or partially. In the modalities, several shimming paths are arranged in a common plane and are commonly oriented in a substantial way. The shimming paths can be parallel or substantially parallel over a part of their entire length, and in modalities they can comprise two or more substantially straight regions separated by rapid changes of direction. Thus, in alternative modalities, through its length a given shimming path can be substantially straight, slightly or substantially curved, having one, two, three, four, five, six or more sudden changes in direction, can form an acute angle, they can form a zigzag, or they can form any other configuration desired by a user. It will be understood that where the paths are arranged on a common plane, the plane itself can be curved or moved in one or more directions at one or more points. In the modalities a path can have a geometry that is arranged on a plane or on a substantially two-dimensional surface.
[0053] In this disclosure, the term "orientation" or "oriented", where used in relation to the shimming paths, indicates the general alignment of the path, based on the positions of the extremities of the portion of the path that are arranged in a shimming panel. Thus, even if the configuration of a number of paths comprises multiple changes of direction, as long as their ends are generally oriented or aligned along a common axis, those paths are referred to as having a common orientation. Similarly, the orientation of a shimming panel is defined in relation to those of its ends or surfaces that comprise ends of the shimming paths.
[0054] In this disclosure, a shimming "current" refers to the current applied to a shimming path and can have any suitable value, in magnitude or signal, for its desired purpose. of a range delimited by the selected values of the group consisting of approximately - more or less 1mA, 2mA, 3mA, 4mA, 5mA, 6mA, 7mA, 8mA, 9mA, 10mA, 20mA, 30mA, 40mA, 50mA, 60mA, 70mA, 80mA, 90mA, 100mA, 110mA, 120mA, 130mA, 140mA, 150mA, 160mA, 170mA, 180mA, 190mA, 200mA, 250mA, 300mA, 350mA, 400mA, 450mA, 500mA, 550mA, 600mA, 700mA, 800mA, 900mA, 1000mA, 1500mA, 1000mA, 1500mA 2000mA or more than approximately 2000mA or - 2000mA It will be understood that in the modalities the direction of a shimming current can be reversed and that any reference to a value for a shimming current comprises or considers both positive and negative orientations or directions , of such current, which will be promptly selected by here they are well versed in technique.
[0055] In the specific modalities, the shimming current in a given shimming path can flow in any direction along the path or predominantly in one direction, and can vary from a current value of approximately 0mA to approximately a maximum value, J. This maximum value J can be approximately 1mA, 2mA, 3mA, 4mA, 5mA, 6mA, 7mA, 8mA, 9mA, 10mA, 20mA, 30mA, 40mA, 50mA, 60mA, 70mA, 80mA, 90mA, 100mA, 110mA, 120mA, 130mA, 140mA, 150mA, 160mA, 170mA, 180mA, 190mA, 200mA, 250mA, 300mA, 350mA, 400mA, 450mA, 500mA, 550mA, 600mA, 700mA, 800mA, 900mA, 1000mA, 1500mA, 2000mA or more than approximately 2000mA. Similarly, in specific modalities and if desired, the minimum value for a current can be selected from the following range of values.
[0056] In this disclosure the term "orthogonality" means that a specified scalar product of functions is zero when evaluated between the individual geometric components of the field. Those skilled in the art will recognize that orthogonal field correction may be desirable so that individual geometric components of inhomogeneity can be adjusted widely independently and is approximated in conventional large-scale nuclear magnetic resonance spectrometers, which may have multiple overlapping coils. or other conductive shapes in a cylindrical coil shape, with each coil or shape predominantly responsible for a specific orthogonal geometric component of the magnetic field, with each geometric component related to a spherical harmonic function.
[0057] In this disclosure the term "primary magnet" refers to one of the magnets contributing to a primary magnetic field for use in magnetic resonance applications. In the modalities there can be two or more of such primary magnets and the homogeneity of the field (referred to as the "primary field") between them can be modulated or improved by using paving paths.
[0058] In this disclosure the term "polar piece" refers to pieces of magnetically permeable material placed in the vicinity of primary magnets for use in contributing to, or shaping, the primary magnetic field. It will be understood that the polar parts may have elongated faces and may be in the form of plates of an appropriate shape.
[0059] In this disclosure the term "primary" or "primary" or primary or primary magnetic field means the primary field generated in an apparatus for MRI applications.
[0060] In this disclosure the term "sample volume" refers to a volume of space in which a sample can be placed and exposed to a primary or primary magnetic field for the purpose of detecting the magnetic resonance properties or the sample, including determining the presence , absence or characteristics of magnetic resonance in the sample. The sample volume can be of any suitable size and can be closed, or partially closed; it may be able to be a vacuum or partial vacuum or to be a controlled atmosphere. In the embodiments, the sample volume may have polar parts, shimming paths, shimming panels and such other devices around it as necessary or desirable. In specific embodiments, the sample volume may or may be within or may comprise a hexagonal or cylindrical cavity or other molded cavity; and can be limited by one, or more, or a plurality of magnets.
[0061] In this disclosure, the term "pseudo-inverse" means a pseudo-inverse Moore-Penrose, or a pseudo-inverse of linear operators or matrices and is also referred to as a "generalized inverse". As an illustration, for matrix A, its pseudo-inverse A + is a generalization of its inverse matrix, and is equal to the inverse of A if A is an invertible square matrix. More precisely, the pseudo-inverse A + of A is the matrix with the properties 1) 1) AA + A = A, 2) A + AA + = A +, 3) AA + and A + A are Hermitians. In the modalities a pseudo-inverse can be used to establish an acceptable solution with the best fit for a series of equations or to find the optimal solution for a system of equations. In the modalities a pseudo-inverse can be calculated by decomposing a singular value in a digital computer using many standard computational packages, for example, Mathematics ™, by Wolfram Research ™.
[0062] In this disclosure the term: "unit current" means an arbitrarily chosen standard current value. As an example and not as a limitation, a unit current can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more milliamps, or more or less. A "unitary shimming field" or a "unitary field" refers to the magnetic field generated by a unitary current flowing through a path.
[0063] In this disclosure, a reference to "modulating" a magnetic field or an inhomogeneity that can be understood in it, refers to imposing one or more desired limitations on the configuration of the field at any point in space. Thus, modulation generally refers to achieving a desired change.
[0064] In this disclosure "to suppress" an inhomogeneity refers to any adjustment to the geometric components of a magnetic field to correct or smooth or otherwise overcome unwanted irregularities or distortions in the field. Suppression can be complete or partial and can affect one or more geometric components. In specific embodiments, suppression can be triggered to cause a magnetic field to adopt a predetermined desired degree of homogeneity.
[0065] In this disclosure a reference to a "component" of a magnetic field refers to a vector component of the magnetic field, which can be in any direction. Reference to a "component" of an inhomogeneity refers to a geometric component, which may, without limitation, include any functional components, such as the functions of x, xy, or ½ (x2 - y2), for example, expanding of the magnetic field in a set of such functions.
[0066] In this disclosure, "estimating" a parameter, such as a field, a field component, inhomogeneity component or a current, comprises making an evaluation, which can be of any desired degree of accuracy, related to any aspect of the parameter, and can include direction, magnitude, polarity, geometry, rate of change, or the like. Estimation can be obtained through a variety of methods including simulating a field, calculating a field, measuring a unit field, mapping a field, or any other suitable method, a variety of which will be readily apparent for those skilled in the art.
[0067] In this disclosure the term "geometry" when used with reference to a shimming path, shimming current, shimming panel, shimming field, magnetic field or the like, refers to both the spatial arrangement of the components and the overall position of the structure being considered. Thus, an indication that a shimming path can be used to modulate more than one component of a magnetic field without any change in the geometry of the shimming path indicates that such a result is achieved without changing the physical layout of the path and shimming by flexing or remodeling it, and also without moving the entire shimming path to a different location or spatial orientation.
[0068] In that disclosure, any structures or portions of structure can be considered from, consist of or comprise any suitable materials. For example, in the form of polar parts or any other magnetically permeable components, they can be constructed from highly permeable materials such as Mu-metal or permalloy, and these and other materials can be sold under trade names or trademarks such as Carpenter Hymu80. Carpenter High Permeability 49, Ni49 or Liga 4750. Those skilled in the art will readily select, adapt, and work with materials suitable for any given application. MODALITIES
[0069] Modalities of the invention are explained with general reference to Figures 1 to 14. First Mode
[0070] In a first general modality, methods are revealed to suppress inhomogeneities in a magnetic field and a device to put on a magnetic field. The apparatus and method can be understood from or implemented in an MRI detector. The Method can be broadly defined as a method for putting on a magnetic field, the method characterized by the use of a single shimming current to suppress more than one geometric component of an inhomogeneity in the magnetic field. The revealed apparatus can be a detector to detect magnetic resonance in a sample exposed to a main magnetic field, the detector characterized by the use of an individual shimming path to suppress more than one geometric component of a magnetic field inhomogeneity in which the The path extends from a first end of a support to a second substantially opposite end of the support. In an alternative formulation, the modality comprises a paving apparatus for paving a magnetic field having two geometric components, the apparatus comprising a shimming path and characterized in that the apparatus is operable to suppress the inhomogeneities in different geometric components of the magnetic field by changing the magnitude of a current applied to the path while the geometry of the path remains constant or substantially constant. The embodiment also comprises a shimming panel that has first and second substantially opposed ends and comprising a plurality of shimming paths each extending substantially between the ends of an MRI detector comprising contacts for receiving such a shimming panel.
[0071] A further variant of the modality comprises a method for choosing the currents to be applied to a plurality of shimming paths, the method comprising estimating the magnetic field produced by applying a known current or a unitary current to the plurality of shimming paths, discovering the geometric components of a magnetic field and its inhomogeneity generated by the current paths using a scalar product of functions; arrange the values obtained as geometric components in a matrix; and choose the applied currents according to the values in a pseudo-inverse of the matrix. The estimate can comprise mapping the magnetic fields, measuring the magnetic fields or simulating the magnetic fields and can understand the estimation of the image currents.
[0072] For simplicity, specific aspects of the modality and any variants of it will be described separately and particularly the method adopted to calculate the shimming currents used to generate shimming fields will be described separately from the physical architecture. A. General Physical Model of a Modality
[0073] A block diagram of a general form of a first generally indicated embodiment 10 is described initially with general reference to Figure 10 and may comprise a power source or power input 16, a control system 12, current isolating circuitry 14 , a generator 27 for generating a primary magnetic field, and polar pieces 28, shimming panels 18, 18 'having associated shimming paths, spectrometer circuitry 22, and a defined sample volume 25 to accept a sample that can be contained within a sample containment device or sample tube 24. It will be seen that the shimming panels are provided in two opposing combinatorial pairs, designated 18 and 18 '. Thus, in an embodiment of the first embodiment, the four shimming panels may comprise two mutually opposing shimming panels which each have eight shimming paths; and two mutually opposite shimming panels which each have 24 shimming paths.
[0074] One embodiment may be or comprise or be comprised of an integrated apparatus for detecting or measuring magnetic resonance in a sample. In specific embodiments, the apparatus may be any form of magnetic resonance detector and may be or comprise an NMR spectrometer, or an NMR image former. The apparatus may be portable and may be a compact apparatus with a floor area of less than 3,000, less than 2,000 or less than 1,000 square centimeters. The unit can be light, and in modalities it can weigh less than approximately 50, 40, 30, 25 or less than approximately 20 kilograms, so that it can be portable for men. Any suitable form of construction and any suitable form of control system can be adopted, but in specific modalities a device can be controlled from an integrated touch screen and can have an optional remote control and data processing feature. The entire system can have substantially automated system controls, optimization routines and data management.
[0075] Specific modalities may comprise a static magnet, and may comprise polar parts. The device can comprise any number of shimming boards or panels. Homogeneity optimization and control apparatus, a frequency generation and measurement apparatus and a system control computer can all be provided. The shape, size, construction dimensions and arrangement of the components can all be adjusted in ways that will be readily understood by those skilled in the art.
[0076] Specific aspects of the first general modality are now described separately. 1. Shimming panels and polar parts
[0077] Shimming panels carry conductive shimming paths. In the first modality, four shimming panels are provided, two of which carry eight shimming paths each and two of which carry 24 shimming paths individually. The panels can be arranged so that the two panels with 24 shimming paths are mutually opposite and the two panels with eight shimming paths are mutually opposite. In the first embodiment, a shimming panel comprises a plurality of shimming paths and has two substantially opposite or mutually spaced ends. The paths can extend between connectors, one connector being close to the first end of the panel and the second connector close to the second end of the panel.
[0078] The shimming panels or shimming paths can be placed on or near the surface of the parts and pole. In one embodiment, this can be done by placing the shimming paths on the panels (such as circuit boards), and placing the panels on the surface of the polar pieces as shown in Figure 5. In Figure 5, the shimming panels or pathways shimming 90 are placed on polar pieces 80. Examples that do not limit the construction for these panels are traces of copper, aluminum, gold or silver in a circuit panel, or similar metals, embedded in a panel; made using a low-temperature ceramic (LTCC) process.
[0079] In the first modality, each current path is not in itself correlated to an orthogonal geometric component specific to the field. More precisely, each path produces a field profile that can be readily calculated. Part of this calculation considers the effect of the current on the polar part, which responds with a magnetic field that can enlarge the magnetic field of the applied current through an "image current" on the polar part. To build orthogonal components of the field, the currents are controlled in combination.
[0080] In the modality, such non-orthogonal inhomogeneity correction can be used in combination with molded polar pieces that can amplify the curb currents through an image-current effect. In the modalities this can, through the presence of ridges with ridges of a polar piece, which are designed to suppress a predominant geometric component of the global inhomogeneity, make the necessary shimming currents smaller than otherwise might be required. This can have the effect of reducing total energy consumption and heat dissipation.
[0081] For example, passing 200 milliamps of current through one of the paths in Figure 7 produces a field profile in the xz plane that is shown in Figure 8. The x and z coordinates are in millimeters and the field, Bz, is in micro tesla. Figure 9 shows a field profile produced using a combination of currents in two shimming panels of the type shown in Figure 7. It will be seen from the figures that one panel is placed on a pole piece, and the other is placed on the pole piece opposite.
[0082] In alternative embodiments, an individual shimming panel may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70 or more shimming paths. In alternative modalities, as many or at least as many or more than approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. 13, 14, 15, 16, 17, 18 , 19, 20, 21, 22, 23, 24, 25, 26, 28, 30, 32, 34, 36, 38, 40, or more individual shimming panels can be provided. In the modalities groups of shimming panels, such as opposite pairs of shimming panels, or groups of e, 4, 5, 6 or more shimming panels, can be configured in mutual opposition or otherwise arranged to provide balanced contributions to the main field paving.
[0083] In the embodiments, the main magnetic field generated by an apparatus has a longitudinal axis and one or more of the shimming paths can be oriented so that its length substantially corresponds to the longitudinal axis of the main field.
[0084] In specific embodiments, a shimming panel may comprise first, and second, substantially mutually spaced or opposite ends and may comprise several shimming paths each extending substantially between the ends. A magnetic resonance detector according to one embodiment can comprise contacts for receiving a shimming panel of such a model, so that an energized set of contacts for receiving a first end of the shimming panel can be paired with a suitably positioned set of contacts oppositely polarized or grounding, all positioned so as to form conduction coupling with the ends of the paths and to apply the selected current values to them.
[0085] In the embodiments, the shimming panels can be rectangular and can be substantially flat. In alternative modalities, the shimming panels can have any suitable shape and can be in one layer or in multiple layers and can be flat or curved. Numbers of shimming paths can be parallel or partially parallel throughout their length or part of their length.
[0086] Figure 6 shows schematically a generally numbered configuration 100 with parallel shimming paths 101 extending between ends or contacts 103, 104 at ends 110 and 120 of the panel. Figure 7 shows an alternative configuration designated 200 with two layers of paths, one shown as solid lines 201 and the other as dashed lines 202. Each path has ends or poles 231 and 232 that end close to ends 220 and 210 of the panel.
[0087] Figure 11 shows an additional alternative configuration for a shimming panel. The panel shown in Figure 11A and generally designated 300 comprises several paths, individual paths being generally designated 330 and arranged in layers, each layer being separately illustrated in Figures 11B, C, D and E for clarity. Each individual path of a first set of paths 340 is shown in Figure 11E. Each of the shimming paths has opposite ends 301, 302 and is oriented so that the ends of the paths are close panel ends 310 and 320, respectively. It will be seen that in this model, and as shown particularly in Figure 11A and 11E, each path may comprise three substantially straight and parallel regions designated 332, 334, 336 which are interspersed with changes in direction which may be sudden or angular changes in direction.
[0088] It will be seen that in the illustrated model the group of paths shown in Figures 1B and 1E are substantially mirror images, and that the paths shown in Figures 11C and 11D are also essentially mirror images.
[0089] The paths 330 as shown in Figure 11B extend from the ends 361 from the upper right of the panel 300 to the end 362 from the lower left of the panel. As shown in Figure 11E, paths 340 extend from the ends 341 on the upper left of the panel to the end 342 on the lower right of the panel. Similarly, panel 300 comprises additional paths 360 which also extend from the upper right to the lower left and 370 which extend from the upper left to the lower right. It will be understood that in this modality groups of paths are provided in different layers.
[0090] It will be understood that the shimming paths of alternative models can comprise 1, 2, 3, 4, 5; or any plurality of straight or substantially straight portions, or curves, or changes in direction; and that the arrangement and relative length of such portions of the shimming paths are similarly variable and can be adjusted or selected as desired by a user. There is no specific need for shimming panels that are used in combination within a specific modality to be of the same shape, dimensions, number of layers or model, although such similarity limitations may be useful in certain applications. In the modalities, there is no specific need for the shimming panels to exhibit reverse or rotational symmetry, although this may be desirable for some applications. A possible asymmetric embodiment is shown in Figure 14 in which a panel generally designated 400 carries a first set of paths 410 and a second set of paths 420, which are inverse images of each other. It will be understood that in the modalities the different groups of paths, or subsets within such groups, can be arranged on different layers or planes, or on opposite sides of panel 400.
[0091] It will be understood that the contacts for applying current to the paths of a shimming panel may be at or near the ends of the panel. Referring now to Figure 10, it will be seen that a sample can be inserted into the detector along an axis, and in use a shimming panel and its cooperating detector can be configured so that a panel and its associated paths are usually oriented along of the sample insertion shaft.
[0092] In the embodiments a shimming panel can be or can comprise or can be comprised of a printed circuit board or a low temperature baked ceramic plate or a flexible polymer such as mylar or an alumina substrate. The panels can be connected to the power and control circuits through direct connection, wire cable or ribbon to a digital or analog control interface. The current supply return paths can be routed behind the polar parts or outside the primary field, producing measures to shield the sample volume against the effect of its magnetic field.
[0093] With the guidance provided here and general common knowledge in the art, those skilled in the art will promptly select suitable numbers of shimming paths and shimming panels, adopt appropriate geometries for the shimming paths and shimming panels, and readily configure the resulting apparatus, for a selected application.
[0094] A static magnetic field produced by permanent magnets, or electromagnets, can be particularly homogenized by ferromagnetic polar pieces, a possible configuration for which is illustrated in Figures 4 and 5. These polar pieces 80 can be two parallel plates, substantially rectangular oriented perpendicular to the direction of the static magnetic field. Although the poles are useful for concentrating and homogenizing the field, especially from a permanent magnet arrangement, the edges of the poles can suffer from non-uniformity of the field due to the dispersion effects of the field between the opposite poles. In the modalities, the polar pieces are, therefore, shaped in such a way that the dispersions of the field at the edges are minimized. In particular, a raised edge 72, displaced from the face 70 of the polar piece by a distance 74 is designed to minimize the inhomogeneities associated with the short axes of the substantially rectangular polar pieces. This is illustrated in Figure 4. Polar parts 80 can increase field strength and homogeneity especially along the horizontal axis (y) as shown in Figure 2 showing the hexagonal cavity 50 within which a pole sample 52 and parts polar are inserted. As will be seen from the view shown in Figure 4B, the polar pieces can be widened and can have ridges 72 at the enlarged edges to increase the field at the edges or extensions of the polar pieces. As will be seen from Figure 4A, the polar piece may be generally rectangular and, in particular, it may be longer along the axis parallel to the ridges than along the axes perpendicular to the ridges. In cross section, as shown in Figure 4B, the pole piece can be largely trapezoidal, with the base of the trapezoid comprising a recess for receiving a shimming panel. Figure 4C shows detail of the enlarged outer edge with its raised ridges 72.
[0095] Figure 3 shows the general arrangement of the main magnets 60 around a channel 50 that accommodates the polar and sample pieces as shown in Figure 5, the arrows 62 show the predominant magnetization directions of each magnet in the arrangement.
[0096] The practical range of dimensions for the thickness and width of the polar parts can vary, based on field strength and homogeneity requirements, as well as sample volume restrictions. The length of the longitudinal axis (x direction) can vary from the length of the sample volume to even longer than the magnet arrangement itself. In the embodiments, the polar pieces can be laminated or otherwise divided into layers interposed with thin insulating layers to reduce eddy currents within the polar pieces.
[0097] Figure 3 shows an array of magnets used to generate a primary field of the modality. It will be seen that several hexagonal magnets are packed together to leave a central longitudinal hexagonal cavity in which two dimensions perpendicular to the length of the channel are designated x and y for the purpose of further reference. Figure 2 further illustrates the geometry of the central hexagonal channel, with a longitudinal axis x, and the two mutually perpendicular axes y and z which are also perpendicular to the x axis.
[0098] • Eles devem preencher uma fração substancial do espaço de sonda (o espaço entre os ímãs) enquanto mantendo o espaço para o volume de amostra designado e os painéis de shimming. Isso pode aumentar a resistência do campo em adição ao objetivo desejado de homogeneizar o campo. • Deve haver bordas elevadas nas peças polares se estendendo ao longo das bordas longas próximas ao volume de amostra de modo que os efeitos de borda associados com a derivada ∂2Bz/∂y2 ∂2Bz/∂y2 são reduzidos. O tamanho dessas cristas pode ser calculado utilizando-se simulações magnetostáticas de elemento finito. • Em algumas variantes dessa ou de outras modalidades, pode ser desejável ter cabeamento elétrico fixado aos caminhos de corrente nos painéis de shimming e se estendendo até o conjunto de circuitos de controle estendidos atrás das peças polares, isto é, no lado oposto ao volume de amostra, ou fora do conjunto de ímã primário. Figure 5 shows the positioning of the polar pieces 80 in a magnet arrangement and also illustrates the positioning of the shimming panels 90 at their extended ends, which are oriented towards a sample 52. For clarity, only those magnets in the magnet arrangement that are closest to the probe space are shown in Figure 5. As will be seen, the polar parts extend through the central cavity of the magnet arrangement, and the trapezoidal cross section allows them to fit longitudinally in that place. The trapezoidal bases, with their associated 90 shimming panels, are mutually opposite and the sample volume with the sample is between them. The polar parts can be made of a material with a high relative magnetic permeability (for example, above 3,000) so that the surfaces of the polar parts serve substantially as equipotentials of the magnetic potential, with the magnetic field substantially perpendicular to these equipotential surfaces. Some examples of suitable materials include permalloy, Mu-metal, sweet iron (coated to prevent rust), or high permeability alloys and cobalt or nickel. In the specific modalities, the following three non-limiting criteria can be useful in specifying the shape of the polar pieces: • They must fill a substantial fraction of the probe space (the space between the magnets) while maintaining space for the designated sample volume and shimming panels. This can increase the resistance of the field in addition to the desired goal of homogenizing the field. • There should be raised edges on the polar pieces extending along the long edges close to the sample volume so that the edge effects associated with the ∂2Bz / ∂y2 ∂2Bz / ∂y2 derivative are reduced. The size of these ridges can be calculated using finite element magnetostatic simulations. • In some variants of this or other modalities, it may be desirable to have electrical wiring fixed to the current paths in the shimming panels and extending to the set of control circuits extended behind the polar parts, that is, on the side opposite to the volume of sample, or outside the primary magnet assembly.
[0099] It will be understood that a shimming path can be triggered in conventional ways by applying a shimming current through it, to generate a pavement field. This can be controlled via digital / analog converters with analog current amplifiers. The microcontroller used to adjust the shimming currents can have resolution requirements ranging from 200-1000 uA and the total range can be from -200 to 200 mA. In alternative modes, shimming currents may have resolution requirements between approximately 0-100, 0-200, 0-300, 0-400, 0-500, 0-600, 0-700, 0-800, 0-900 and 0 -1000 uA. In the modalities the total range of the shimming currents can be from approximately -200mA to approximately + 200mA and in the modalities it can be between approximately -300 and +300 mA, between approximately -250mA and + 250mA, between approximately -200mA and approximately + 200mA, between approximately - 150mA and approximately + 150mA, between approximately -100mA and approximately + 100mA, between approximately -50mA and approximately + 50mA, or above approximately -300, -250, -200, -150, -100, -50, 0 , +50, +100, +150, +200, +250, +300 or more milliamps.
[0100] In the embodiments, field homogeneity can be monitored by analyzing the NMR signal format of a known, standard compound. Field homogeneity can also be monitored through the strength of the blocking signal and shimming control currents can be adjusted through an automated routine that sequentially varies the current in the individual paths and monitors the resulting change in the intensity of the blocking signal or shape of NMR signal. This procedure can be extended for paired and higher order adjustment of multiple paths simultaneously using a heuristic learning algorithm analogous to a variable length execution average calculation of a type used in multi-input process control. 3. Sample Probe and Sample Volume
[0101] A sample can be maintained by a probe and a sample and kept inside a sample tube that can be inserted into a detector. The volume assigned to a sample in one embodiment is a cylinder 5 mm in diameter and approximately 2 mm in length, and the desired magnetic field can be substantially perpendicular to the axis of symmetry of that cylindrical volume. The space for inserting the sample in this mode can be a hexagonal prism with a 22 mm flat / flat cross-section and 125 mm in length, with access to the field correction device only available through the end caps of the prism.
[0102] The probe can hold the sample in the longitudinally aligned center of the main field generating magnet in a position such that the sample is centered on the long axis of a transmit / receive coil.
[0103] Figure 2 shows two views of a hexagonal prism with a designated volume shown internally. To facilitate the discussion, a coordinate system is defined in the figure. The axis of the sample volume of cylindrical symmetry is along the x direction, and a strong, uniform magnetic field in the z direction is desired. One way to produce this field is to mount the cylindrical magnets or prismatic magnets with hexagonal cross section in a pattern involving the probe space. If the magnets are magnetized substantially uniformly and in a "diametrical" manner, so that each magnetization axis of the magnet is perpendicular to its predominant axis of symmetry, then a suitable magnet arrangement is shown in Figure 3. An array of vectors of magnetization like this is sometimes called "Halbach cylindrical arrangement", which is known to perform a substantially homogeneous field within the arrangement.
[0104] Those skilled in the art will readily understand the necessary design characteristics and material parameters of a sample probe for use in the modalities. In modalities and applications involving proton-NMR, the sample probe, or parts of it, can be constructed of a material that has a low concentration of protons. In alternative modalities and for alternative applications, it may be desirable or necessary that the probe or part of it has a low concentration of the relevant carbon, fluorine, phosphorus and other magnetically resonant nuclides. In the embodiments, the probe can be designed to accommodate flow applications where the sample flows into the probe through a tube and into a cell.
[0105] A sample probe can contain one or more coils regulated individually and separately for proton, fluorine, carbon, phosphorus or other active magnetic resonance nuclide; or paired in combinations of two or more of the same. In the specific alternative modalities there may be additional coils and there may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more coils.
[0106] In the modalities, probe regulation capacitors, inductors, or other reactive elements can be connected to the RF architecture through SMA or BNC connectors and can be adjusted electronically or manually. A probe set may include a temperature control sensor. The tuning elements can be connected to a monitoring and adjustment circuit which, when combined with a suitable microprocessor and optimization routine, can enable automated tuning of the circuit.
[0107] In one embodiment, the sample can be confined to a cylinder of a specified length and diameter. In another embodiment, it can be a flat sample adhering to a substrate surface that could be moved to a detection region. A range of alternative configurations may be possible for specific applications. In any case, one can calculate or estimate an appropriate weighting function, W (x, y, z), which can be used to estimate the relative contribution to an NMR signal that is due to the turns in a volume element close to the position defined by the x, y, z coordinates when such a signal is detected by a transmit / receive coil. This function can be used to define a scalar product suitable for use in defining the appropriate orthogonal shoring functions. 4. Transmission and Reception Coil
[0108] In the modalities a coil or coils to apply pulses of oscillating magnetic fields to a sample and to monitor the magnetic effects of these magnetic fields applied on the sample can be of any desired length, diameter and other dimensions, as may be desirable to accommodate a given size sample or format. In specific embodiments such transmission / reception coils may be between 8 and 12 mm long, or may be up to, or less than, approximately 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 , 15, 16, 17, 18, 19, or 20 mm, or up to approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30 or more centimeters or can be within a range whose limits are defined by any combination of some of the preceding values. In the specific modalities selected, the diameter of the transmission / reception coils can be between approximately 8 and 9 mm; between approximately 9 and 10 mm; between approximately 10 and 11 mm; between approximately 11 and 12 mm; between approximately 12 and 13 mm; between approximately 9 and 11 mm. In the embodiments, the transmission / reception coils can have a diameter of at least approximately 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm or they can have a diameter no greater than approximately 1 mm, 2 mm, 3 mm , 4 mm, 5 mm, 6 mm or more and in alternative modalities the transmission / reception coils may have a diameter of no more than approximately 5.3 mm, or may have a diameter greater than or less than approximately 1 mm, 2mm, 3mm, 4mm, 4.1mm, 4.2mm, 4.3mm, 4.4mm, 4.5mm, 4.6mm, 4.7mm, 4.8mm, 4.9mm, 5mm, 5.1mm, 5, 2mm, 5.3mm, 5.4mm or more. Transmission / reception coils can be commonly constructed from copper wire or other suitable conductors supported by Teflon, polyimide or ceramic or other suitable materials.
[0109] Although selected geometries for the transmission / reception coils are revealed, in alternative modalities the coils can be of larger or smaller diameters or of lengths or shapes to satisfy the specific requirements of the modality and all necessary changes in dimensions and configurations will be promptly made and implemented by those skilled in the art. 5. NMR magnet
[0110] Figures 3, 4 and 5 show possible arrangements and magnet models of a modality. Shimming panels, polar parts and sample probe assembly can be inserted into a magnet assembly that is responsible for the generation of a static NMR magnetic field. In one embodiment, the magnet model can be related to Halbach magnets in which the static magnetic field is produced using an array of permanent magnets formed from stacked cylindrical magnet shelves, the permanent ones of which the cylindrical axes are or can be substantially parallel to each other, however, each of whose magnetization axes are substantially perpendicular to the common direction of the cylindrical axes and cylindrical magnets is in hexagonal sleeves mounted in an arrangement.
[0111] In the modalities the resistance of the magnetic field can be between 1.3 and 1.6 Tesla (proton frequency of 56 - 68 MHz), but those skilled in the art will readily consider that in the alternative modalities the magnetic field can be between approximately 0 and 0 , 5 Tesla, between approximately 0.5 and 1 Tesla, between approximately 1 and 1.2 Tesla, between approximately 1.2 and 1.4 Tesla, between approximately 1.4 and 1.6 Tesla, between approximately 1.6 and 1.8 Tesla, between approximately 1.8 and 2.0 Tesla, between approximately 2.0 and 2.2 Tesla, between approximately 2.2 and 2.4 Tesla, between approximately 2.4 and 2.6 Tesla, between approximately 2.6 and 2.8 Tesla, between approximately 2.8 and 3.0 Tesla, or as high as 3T (129MHz) or higher. In specific alternative embodiments, the magnet elements can be made of neodymium-iron-boron or cobalt-samarium materials or any other suitable magnet materials and the magnet assembly support frames can be machined from aluminum, polyimide or Teflon or other materials.
[0112] The magnet assembly can be shielded against external magnetic interference by a closure constructed of material of high permeability and can be temperature monitored and controlled through the use of heaters, Peltier coolers and / or feedback control device. The magnet can be mounted on a vibration suppression system. The primary magnetic field can be monitored and adjusted using a second spectrometer circuit that is tuned to a second isotope, such as deuterium, different from the isotope to be examined for magnetic resonance properties. The system can monitor the frequency of deuterium resonance and adjust the transmitter / receiver circuit or the temperature or one or more currents in the field production conductors in any combination to account for real-time variations in the primary magnetic field accordingly. B. Signal Generation and System Control
[0113] A device's modalities may comprise a user interface, device and method for generating, switching, transmitting and receiving radio frequency signals, pulse program controller, device for digitizing and storing signals, data system, temperature management, monitoring and system status control, input and output display. In the modalities the system can require 120 volts of energy or 240 volts of energy and can be configured to be operable using common household and commercial outlets and regular sources of electrical power. 1. Calculating shimming currents and controlling shimming currents
[0114] One aspect of the modalities is a method for putting on a magnetic field or suppressing inhomogeneities in the magnetic field. In the modalities the method and the apparatus using the method can avoid the use of individual shimming strokes or shimming coils, each of which corresponds to an individual geometric component of the inhomogeneity of the magnetic field. A plurality of shimming paths can have a substantially common orientation, but they can be operable to suppress a plurality of geometric components from an inhomogeneity. In specific embodiments, the shimming paths can avoid inversions of direction, can be essentially linear, and can have a first end that is positioned next to a first end of a shimming panel and a second end that is positioned next to a second end of a shimming panel. In the modalities, the shimming fields generated by one or more shimming paths, or generator collectively by all shimming paths, can be modulated by adjusting the magnitude of the current that flows through the shimming path or paths. In addition, in the modalities the methods and devices disclosed can be used to generate a plurality of shimming field configurations, capable of modulating a plurality of geometric components of the primary magnetic field and any inhomogeneities in that place, without the need to modify the orientation or shape or geometric configuration of the shimming paths.
[0115] In another modality, the geometry of the shimming paths is not limited by the need to provide individual shimming paths corresponding to each of the geometric components to be modulated.
[0116] Broadly speaking, the shimming currents to be applied to the individual shimming paths to effectively suppress specific geometric components of inhomogeneity in the primary field are determined by estimating or mapping the shimming fields generated by unitary currents in one of the shimming paths. The resulting fields are then presented as a matrix, which can be a 25 x 64 matrix (where 64 shimming paths are provided to collectively modulate 25 geometric components or spatial shimming dimensions) introduced in a Moore-Penrose pseudo-inverse analysis. The pseudo-inverse analysis thus calculated then used to determine the currents that must be applied to the shimming paths to generate the desired geometric components of inhomogeneity, which can be additionally used as corrections for the magnetic field to suppress inhomogeneities in that place.
[0117] In the embodiments, the revealed devices can generate image currents in permeable materials, and the methods of calculating the appropriate shimming currents therefore incorporate a tolerance for the effects of such image currents. Generation of a set of shimming functions for a set of potential shimming paths
[0118] (a) Começar com s funções "básicas" de valor real de coordenadas espaciais, por exemplo, coordenadas Cartesianas x, y, z com z ≤ c. Essas funções pj(x, y, z) devem ser soluções para a equação de Laplace, ∇2ρj = 0 , de modo que elas são adequadas como campos magneto estáticos. Elas devem também incluir como partes dos polinômios de ordem inferior nas coordenadas, por exemplo, 1, x, y, z, x2, xy, etc. de modo que elas são adequadas como termos em uma expansão matemática de uma função de campo. Com amostras cilíndricas, um conjunto conveniente de funções básicas são as combinações lineares de valor real ou funções de harmônico esférico Yl.m até a 2 ordem 1 = n, com n2 ≤ c. (b) Definir uma função de ponderação, W(x, y, z) definida dentro do volume de amostra e um produto escalar associado para funções f e g, por exemplo ˂f|g˃ =∫ W(x, y, z) f(x, y, z) g(x, y, z) dV A função de ponderação deve ser grande nas regiões onde giros na amostra são esperados para contribuir grandemente com um sinal medido a partir da bobina de detector; e pequenos onde a contribuição será pequena. Uma classe de funções adequada para uma bobina de detector aproximadamente cilíndrica é W(x,y,z) = aB1(x, y, z)sinbB1(x, y, z), onde a e b são constantes que podem ser usadas para otimizar o sinal total e para normalizar a função de ponderação. (c) Usar um procedimento de ortogonalização de Gram-Schmidt para gerar s funções fj(x, y, z) , as quais são combinações lineares das funções básicas s, que são orto normais com relação ao produto escalar definido na etapa 2. Essas são chamadas de funções de shimming. In the modalities it can be useful to select a set of shimming functions that are orthogonal to a scalar product that is suitable for a desired range of sample geometries. If the shimming functions are orthogonal, then in alternative modalities this can make it easier or faster to suppress total inhomogeneity. This section explains the generation of shimming functions for potential shimming paths where the potential shimming paths are c in number, given a sample volume V and a detector coil with field estimated by unit current B1 (x, y, z) . (a) Start with "real" functions of real value of spatial coordinates, for example, Cartesian x, y, z coordinates with z ≤ c. These functions pj (x, y, z) must be solutions to the Laplace equation, ∇2ρj = 0, so that they are suitable as static magnet fields. They should also include as parts of the lower order polynomials in the coordinates, for example, 1, x, y, z, x2, xy, etc. so that they are suitable as terms in a mathematical expansion of a field function. With cylindrical samples, a convenient set of basic functions are linear combinations of real value or spherical harmonic functions Yl.m up to 2 order 1 = n, with n2 ≤ c. (b) Define a weighting function, W (x, y, z) defined within the sample volume and an associated scalar product for functions f and g, for example ˂f | g˃ = ∫ W (x, y, z) f (x, y, z) g (x, y, z) dV The weighting function should be large in regions where rotations in the sample are expected to contribute greatly to a signal measured from the detector coil; and small where the contribution will be small. A suitable function class for an approximately cylindrical detector coil is W (x, y, z) = aB1 (x, y, z) sinbB1 (x, y, z), where a and b are constants that can be used to optimize the total signal and to normalize the weighting function. (c) Use a Gram-Schmidt orthogonalization procedure to generate s functions fj (x, y, z), which are linear combinations of the basic functions s, which are orthogonal to the scalar product defined in step 2. These they are called shimming functions.
[0119] (a) Mediante integração de forma exata ou numérica da lei de Biot-Savart através do caminho de corrente. (b) Mediante uso da lei de Biot-Savart como em (a) , mas também incluindo correntes de imagem estimadas produzidas em quaisquer materiais de elevada permeabilidade dispostos próximos ao caminho de corrente. (c) Mediante simulação magnetoestática mais cuidadosa utilizando métodos de simulação de elemento finito ou outros métodos de simulação eletromagnética. (d) Mediante aplicação efetiva da corrente e então medindo o campo com uma sonda de magnetômetro. 2. Construir uma matriz Mi,j cujas entradas são os produtos escalares (fi|Fj). As faixas para os índices i e j são 1 ≤ i ≤ s e 1 ≤ j ≤ c. Cada coluna dessa matriz é uma representação do campo magnético Fj projetado nas funções de shimming.3. Construir o pseudoinverso de Moore-Penrose, M+j,i, de Mi,j. Há muitos pacotes computacionais padrão, incluindo Mathematics™, por Wolfram Research™, que farão isso. Aqueles versados na técnica identificarão prontamente e utilizarão pacotes e métodos adequados.4. As colunas da matriz pseudoinversa resultante então conterão listas de números, c em comprimento, que são fatores de escalada que devem ser usados ao se aplicar correntes aos caminhos de shimming para produzir campos magnéticos combinando mais estreitamente com as funções de shimming desejadas (em um sentido de análise de mínimos quadrados).In the modalities it can be useful to generate a set of shimming profiles, which are lists of coefficients, each list having c real numbers, for a given set of shimming paths, also c in number. A given shimming profile corresponds to a desired, determined shimming function. To produce a field function that approximates a desired shimming function, currents are applied to the set of shimming paths, whose currents are proportional to a corresponding number in the shimming profile for that shimming function. This section explains how to generate a set of shimming profiles for a set of shimming functions, corresponding, s in number, that are compatible with a set of shimming paths, c in number, according to the method of the invention. 1. For each current path j, estimate the magnetic field Fj (x, y, z) produced at a set of points within the sample volume that is due to a unit current (1 milliampere, for example) applied to the path. The set of points must be large enough to facilitate the computation of numerical integrals of the type defined in step 2, and must be at least c in number. This can be done in several ways: (a) Through exact or numerical integration of the Biot-Savart law through the current path. (b) Using the Biot-Savart law as in (a), but also including estimated image currents produced from any materials of high permeability arranged close to the current path. (c) Through a more careful magnetostatic simulation using finite element simulation methods or other electromagnetic simulation methods. (d) By effectively applying the current and then measuring the field with a magnetometer probe. 2. Build a matrix Mi, j whose inputs are the scalar products (fi | Fj). The ranges for indexes i and i are 1 ≤ i ≤ if 1 ≤ j ≤ c. Each column of this matrix is a representation of the magnetic field Fj projected in the shimming functions. 3. Construct the Moore-Penrose pseudo-inverse, M + j, i, from Mi, j. There are many standard computational packages, including Mathematics ™, by Wolfram Research ™, that will do this. Those skilled in the art will readily identify and use suitable packages and methods. 4. The columns of the resulting pseudo-inverse matrix will then contain lists of numbers, c in length, which are scaling factors that should be used when applying currents to the shimming paths to produce magnetic fields more closely matching the desired shimming functions (in sense of least squares analysis).
[0120] In a first embodiment, an apparatus is revealed to obtain high magnetic field homogeneity in the magnet systems. In one embodiment, the device combines ferromagnetic polar parts molded with electrically conductive current paths. The paths can be printed on plates suitably sized to form shimming plates, or they can be supported directly on the primary magnets or polar parts, or they can be supported in relation to the primary magnetic field in other ways.
[0121] In one embodiment, the polar parts can be shaped for tight fit within the central hexagonal chamber of a magnet assembly with faces parallel to each other and perpendicular to the static field. Modeling the opposite faces of the polar parts can increase the homogeneity and resistance of the magnetic field. Crests on the opposite polar parts can be raised parallel to the static field and extend parallel to the long axis of the magnet.
[0122] In one embodiment, the polar parts can be parallel to each other and perpendicular to the static magnetic field. The opposite faces of the polar pieces can be raised parallel to the direction of the static field along the long axis of the polar pieces in a calculated optimal position that creates a wide, narrow channel into which a homogenization shimming panel can fit parallel to the polar pieces and seated adjacent to them. In one embodiment such a channel or combined channels can have dimensions of approximately 1x 18 x 150 mm and the shimming plates can be sized to fit within such channels and can themselves have dimensions of approximately 1x 18 x 150 mm. In the embodiments, the plates can have a strip of different dimensions and can be of a thickness so that the exposed surface of the plate is substantially flush with the surface of the polar piece adjacent to the channel.
[0123] Apparatus and methods for suppressing inhomogeneity in a magnetic field are revealed. This can be a field in an MRI device, and it can be in an NMR machine, which can be a compact NMR machine. In the modalities, the shimming panels or shimming paths can allow the device's paving elements to be reduced in size or arranged in desirable configurations. In the embodiments, the paving elements can comprise current, conductive paths that can be applied to a paving plate or to a pole surface and can comprise only one or two layers.
[0124] In one embodiment, an apparatus is revealed to wedge a first magnetic field, the system comprising: two magnetic polar pieces mutually opposed on opposite sides of a volume, and an electrically conductive current path arranged in relation to the volume in order to modulate the current flow. in the current path it is usable to put the magnetic field in a controllable way. In alternative modes the device weighs less than approximately 21 kg.
[0125] In alternative embodiments the device is an NMR machine weighing less than approximately 15 pounds and with a spectral resolution better than approximately 0.1 ppm.
[0126] In one embodiment, a set of magnetic resonance is disclosed comprising a plurality of elongated prisms comprising individually a magnet with a magnetic axis defined in relation to the prism, the plurality of magnets collectively determining a substantially homogeneous magnetic field. C. Example
[0127] The following description is an example of a modality and is only illustrative.
[0128] Figure 13 shows a block diagram of an example of an embodiment, a device for measuring NMR of a liquid sample placed in sample tube 600. Figure 12 shows a top view of main magnet structure 610 in Figure 13, along with other structures placed within the main magnet structure. This main magnet structure is made up of three shelves, each containing 18 magnets, and each magnet is a cylinder or hexagonal prism of a "hard", highly magnetized magnetic material, a suitable material being neodymium-iron-boron with a magnetization of approximately 1.3 Τ / μ0. The shelf structure itself can be made of a substantially non-magnetic material such as aluminum. Each magnet is magnetized almost uniformly and "diametrically", meaning that its magnetization vector is perpendicular to its predominant axis of symmetry. The magnetization vectors of each magnet are arranged in a "Halbach cylinder" arrangement that is shown in Figure 3. The shelves are stacked on top of each other as shown in Figure 13, with the magnetization vectors of each magnet aligned in the same direction as the one above or below it. This arrangement provides a cavity (50 in Figure 3) with a hexagonal cross section, with a magnetic field of the order of 1.2 T inside the cavity. In a preferred embodiment, the hexagonal cavity and the magnets are approximately 22 mm across the hexagon, the magnets themselves are approximately 38 mm high, and the main magnet structure is approximately 130 mm high. 620 non-magnetic spacers, approximately 3 mm thick, can be placed between the magnet shelves.
[0129] Polar parts 630 can be inserted into the cavity of the main electromagnet structure as shown schematically in Figure 13 and Figure 12. These polar parts (shown schematically in Figures 12 and 13) are preferably not as long as the main electromagnet structure itself and can be approximately 76 mm in length. A preferred cross-sectional shape 80 for pole piece is shown in Figure 4, and its alignment with the cavity of the main electromagnet structure is shown in Figure 5. The polar pieces can be made of a soft, high permeability alloy, such as as permalloy or Carpenter ™ high permeability alloy "49". The polar pieces may have a ridge that extends the length of the piece, may be substantially trapezoidal in cross-section, and may have a variable length of material removed from the back surface (the furthest surface from the sample tube 600). If such material is removed from the back of a pole piece, other pieces of magnetic material can be inserted or moved within the resulting space in order to change the actual shape of the pole piece. The presence of these polar pieces, together with these shape changes, can make the field within the rest of the cavity higher than in the absence of the polar pieces (approximately 1.4 T) and more uniform.
[0130] The main shimming panels 640 are placed on the inner surfaces of the polar parts 630. These panels can be 2, 3- or 4-layer printed circuit boards approximately 18 mm across, approximately 160 mm long, and approximately 0 , 6 mm thick. The panels can be mounted with connectors at one or both ends, and the ends can extend outside the main electromagnet structure. Figures 6, 7, 11 and 13 show suitable models for the conductors printed on the layers of the shimming panels. A set of 642 auxiliary shimming panels can be inserted into the cavity of the electromagnet, as shown schematically in Figure 12, and these panels can be approximately 8 mm across, approximately 160 mm long, and approximately 0.6 mm thick . These panels can also have straight conductor patterns (shimming paths) or zigzag-shaped conductors of the types shown in Figures 6, 7, 11 and 13 with the same, lesser, or greater number than the number on the main 640 shimming panels In one model, there are 8 conductors in each of the auxiliary shimming panels 642 and 24 conductors in each of the main shimming panels 640.
[0131] The conductors in the shimming panels are connected to a set of current separators 650 which are connected to a shimming current controller 652, which is controlled during operation of the device by means of a microcontroller 660 using information from a generator. shimming profile 654. These controllers and separators can be implemented in an appropriate combination of computer software and digital and analog electronic media. In a specific embodiment of the example, the current separator circuitry 650 can deliver bipolar currents in the range 0-600 mA or more to the conductors in the shimming panels.
[0132] It may be desirable to monitor and stabilize the temperature of the main electromagnet assembly with a 665 thermal regulator, and so that regulator can be provided in a, and can be controlled by the 660 microcontroller circuitry. The microcontroller can also have an interface established with radio frequency transmission / reception circuit set 670, which provides radio frequency pulses for transmission to a sample winding 676 through amplifier circuit set 674, and which receives response signals from the sample through the set of amplifier circuits 672.
[0133] The microcontroller circuitry, and other parts of the device, can interface with a digital computer 680, which itself can interface with a number of peripherals, such as a 685 display unit or others, such as a printer, file storage system, remote control means, or the like, through cables or wi-fi or other interface means. A 690 power supply unit is provided to provide electrical power, and in a preferred embodiment this power supply can provide approximately 70 W for the operation of the entire unit, but this can be more or less than 70 W in applications.
[0134] The modalities and examples presented here are illustrative of the general nature of the subject under study claimed and are not limiting. It will be understood by those skilled in the art how these modalities can be easily modified and / or adapted for various applications and in various ways without departing from the revealed essence and scope of the study material. The claims of the same should be understood as including without limitation all alternative and equivalent modalities of the present subject under study. Phrases, words and terms used here are illustrative and not limiting. Where permitted by law; all references cited herein are incorporated in their entirety by reference. It will be considered that any aspects of the different modalities disclosed herein can be combined in a range of possible alternative modalities, and alternative combinations of characteristics, all of which varying combinations of characteristics should be understood as forming a part of the present study subject.

权利要求:
Claims (16)
[0001]
Method for homogenizing a magnetic field in which there is an inhomogeneity having more than one functional component, the magnetic field being produced by a set of magnets (610) having two sets of opposite and mutually spaced ends and a set of axis, the characterized method by the fact that it understands: providing a plurality of commonly oriented homogenization paths (101), said homogenization paths arranged on a common surface (100) having two opposite and mutually spaced ends (110, 120), each of said surface end ( 110, 120) having at least one associated electrical connector (103, 104); application of a plurality of individual electronic homogenization currents modulated in a coordinated way along corresponding paths of the plurality of homogenization paths (101), each of said electronic homogenization currents causing said electrical connector (103) to enter said end surface (110), flow from the electrical connector (103) at one said surface end (110) to said electrical connector (104) at the other said surface end (120); and outputting the associated electrical connector (104) at the other said surface end (120); and suppression of more than one functional component of inhomogeneity in the magnetic field using the plurality of homogenization currents, wherein each of said surface end (110, 120) is close to a corresponding end of said set of ends so that at least a portion of said homogenization streams flows from said set of ends towards another said set of ends.
[0002]
Method according to claim 1, characterized by the fact that the sample (600) is inserted into the magnetic field along said axis set.
[0003]
Method according to claim 1, characterized by the fact that each individual stream of the plurality of homogenization currents flows in a respective plurality of homogenization paths (101), and in which the individual currents of the currents are determined by: estimate a magnetic field produced by applying a current known to each of the plurality of homogenization paths (101); compute a scalar product of functions representative of the functional components of the estimated magnetic field to obtain values of functional components; arrange the values of functional components in a matrix; determining a pseudo-inverse of the matrix to obtain pseudo-inverse matrix values; and choose the individual currents among the currents according to the values of the pseudo-inverse matrix.
[0004]
Method, according to claims 1 or 3, characterized by the fact that the application comprises adjusting in a coordinated manner the magnitudes of said homogenization currents.
[0005]
Method according to claim 1, characterized by the fact that the plurality of said homogenization paths (101) are mutually connected to one of said surface ends (110, 120) and said mutually connected end paths are maintained at an electrical grounding potential controlled by external electronic means.
[0006]
Panel for homogenizing a magnetic field (100) characterized by the fact that it has first and second ends of panel (110, 120) substantially spaced and mutually opposite and a substantially flat portion comprising a plurality of homogenization paths (101) conducting electric current extending between and ending at said ends of the panels (110, 120), where individual streams of the homogenizing streams have a substantially common orientation, wherein said electrical current causes each said homogenization path (101) to enter said panel end (110) and be conducted along each said homogenization path (101) and to exit each of said homogenization path (101) at the other said panel end (120).
[0007]
Panel for homogenizing a magnetic field, according to claim 6, characterized by the fact that the panel (100) is adapted so that said panel (100) can be positioned in a channel (50) within a magnetic arrangement ( 600) cooperating so that said homogenization path (101) carries the electric current that extends through the channel (50).
[0008]
Panel for homogenizing a magnetic field according to claim 7, characterized in that each said panel end (110, 120) comprises electrical connectors (103, 104) accessible from the corresponding end of the channel (50).
[0009]
Panel for homogenizing a magnetic field according to claim 6, characterized in that said homogenization panel comprises a printed circuit board.
[0010]
Detector for detecting magnetic resonance in a sample exposed to a main magnetic field, the detector characterized by comprising a homogenization panel as defined in claim 6.
[0011]
Detector according to claim 10, characterized by the fact that it also comprises a longitudinal space (50) having an axis, the longitudinal space (50) for insertion of a sample probe (600) containing the sample along the axis and wherein the orientation is substantially parallel to the axis.
[0012]
Detector according to claim 11, characterized by the fact that it further comprises at least two said flat homogenization panels (100), each mounted on separate pieces of two polar pieces (630), said polar pieces (630) being extending within the longitudinal space (50).
[0013]
Detector according to claim 10, characterized in that at least a subset of the plurality of homogenization paths (101) are arranged on substantially parallel surfaces of the homogenization panel (100).
[0014]
Detector according to claim 10, characterized by the fact that it also comprises a printed circuit board in which the flat homogenization panel (100) is comprised.
[0015]
Detector according to claim 10, characterized by the fact that said magnetic field is at least partially produced by a set of magnets (600) having two opposite and mutually spaced ends and an axis set, and in which each of the two ends of the panel (110, 120) is close to one end.
[0016]
Detector according to claim 10, characterized by the fact that said set of magnets (600) is adapted to receive a sample inserted in said magnetic field along said set of axis, and in which said panel axis coincides with or is substantially parallel to said axis assembly.

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同族专利:

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公开号 | 公开日

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CA2780181C|2019-10-15|

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NZ599837A|2014-01-31|

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CN104459584A|2015-03-25|

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US8712706B2|2014-04-29|

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EP2507643A1|2012-10-10|

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US20140225615A1|2014-08-14|

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AU2010327289A1|2012-05-31|

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CN102640010A|2012-08-15|

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JP2013512442A|2013-04-11|

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WO2011066652A1|2011-06-09|

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BR112012013588A2|2016-07-05|

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CN104459584B|2018-03-20|

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EP2507643A4|2015-08-26|

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JP5818267B2|2015-11-18|

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US20110137589A1|2011-06-09|

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HK1171512A1|2013-03-28|

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CA2780181A1|2011-06-09|

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AU2010327289B2|2015-05-28|

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CN102640010B|2015-11-25|

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法律状态:
2019-01-08| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|

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2019-05-07| B06T| Formal requirements before examination|

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2020-01-28| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|

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2020-11-10| B09A| Decision: intention to grant|

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2021-01-26| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 10 (DEZ) ANOS CONTADOS A PARTIR DE 26/01/2021, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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US26601509P| true| 2009-12-02|2009-12-02|

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US61/266,015|2009-12-02|

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PCT/CA2010/001920|WO2011066652A1|2009-12-02|2010-12-01|Method and apparatus for producing homogeneous magnetic fields|

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