US20110175694A1 - Magnetic assembly and method for defining a magnetic field for an imaging volume - Google Patents

Magnetic assembly and method for defining a magnetic field for an imaging volume Download PDF

Info

Publication number
US20110175694A1
US20110175694A1 US13/000,877 US200913000877A US2011175694A1 US 20110175694 A1 US20110175694 A1 US 20110175694A1 US 200913000877 A US200913000877 A US 200913000877A US 2011175694 A1 US2011175694 A1 US 2011175694A1
Authority
US
United States
Prior art keywords
magnetic field
magnet assembly
magnets
target
magnet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US13/000,877
Other languages
English (en)
Inventor
B. Gino Fallone
Tony Tadic
Brad Murray
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alberta Health Services
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to US13/000,877 priority Critical patent/US20110175694A1/en
Assigned to ALBERTA CANCER BOARD reassignment ALBERTA CANCER BOARD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FALLONE, GINO B., MURRAY, BRAD, TADIC, TONY
Assigned to ALBERTA HEALTH SERVICES reassignment ALBERTA HEALTH SERVICES ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ALBERTA CANCER BOARD
Publication of US20110175694A1 publication Critical patent/US20110175694A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/543—Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3806—Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/08—Deviation, concentration or focusing of the beam by electric or magnetic means
    • G21K1/093—Deviation, concentration or focusing of the beam by electric or magnetic means by magnetic means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N2005/1085—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy characterised by the type of particles applied to the patient
    • A61N2005/1087—Ions; Protons
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N2005/1085—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy characterised by the type of particles applied to the patient
    • A61N2005/1089—Electrons
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A61N5/1043—Scanning the radiation beam, e.g. spot scanning or raster scanning
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles

Definitions

  • the present invention relates generally to magnetic fields with predetermined specially desired characteristics, and more particularly to magnetic assembly and method for defining a magnetic field for an imaging volume.
  • Magnetic Resonance Imaging is a well-known imaging technique during which an object, such as a human patient, is placed into an MRI machine and subjected to a uniform magnetic field produced by a polarizing magnet housed within the MRI machine.
  • Radio frequency (RF) pulses generated by an RF coil housed within the MRI machine, are used to scan target tissue of the patient.
  • MRI signals are radiated by excited nuclei in the target tissue in the intervals between consecutive RF pulses and are sensed by the RF coil.
  • finely controlled magnetic field gradients are switched rapidly to alter the uniform magnetic field at localized areas thereby to allow spatial localization of MRI signals radiated by selected slices of the target tissue.
  • the sensed MRI signals are in turn digitized and processed to reconstruct images of the target tissue slices using one of many known techniques.
  • a strong uniform static magnetic field is required in order to align the nuclear spins of the object within a particular imaging volume.
  • This uniform static magnetic field is normally produced by a permanent or coil magnet assembly with a magnetic field strength on the order of 0.1 to 4.7 Tesla within the imaging volume.
  • the finely controlled magnetic field gradients imposed in the imaging volume allow for discrimination amongst nuclear spins at different locations.
  • inhomogeneities in the static magnetic field within the imaging volume are inseparable from the magnetic field gradients during image acquisition and directly lead to geometric distortions in the resulting images.
  • the opposing surfaces of the magnet pole pieces are contoured in such a way that the pole pieces are shaped axisymmetrically about an axis generally extending towards the opposing pole piece surface.
  • the most common such pole piece design is known as a rose-ring design, in which the surface of the pole piece which is closest to the imaging volume is entirely flat with the exception of a ring of magnetic material placed along the periphery of the said pole piece surface.
  • a graph of axial distance of the pole piece surface along the axis, versus radial distance from the axis is a line of zero slope with a single vertical step at the radial position of the rose-ring.
  • One magnet assembly design disclosed in U.S. Pat. No. 5,539,366 consists of axisymmetrically shaped pole pieces for which a graph of axial distance, of the pole piece surface along the axis, versus radial distance from the axis is a piece-wise linear curve, or is a non-linear curve having a continuous slope with at least two sign reversals. Both such designs are limited in that points on the surface regions of the pole pieces located an identical radial distance from the axis are also located a common axial distance along the axis, and thus only axisymmetric magnetic field inhomogeneities can be reduced prior to shimming. Furthermore, these systems are massive and immobile as the pole piece sizes are necessarily very large, and therefore are not suitable for movement relative to the subject being examined.
  • Such additional devices may be affected by the presence and/or characteristics of the magnetic field at their location and may themselves alter the characteristics of the magnetic field in the imaging volume.
  • the incorporation of such objects or devices within or proximate the magnet assembly may require a particular volume of free space to be vacated from the magnet assembly, such as a large hole through the magnet structure, either for placement of the object or device, or for providing a benefit in performance of the object or device itself.
  • such vacated volumes significantly affect the magnetic field produced by the magnet assembly and contribute to a highly inhomogeneous field in the imaging volume.
  • a magnet assembly comprising:
  • each of the magnets producing a variety of magnetic field strengths across inward-facing surfaces thereof that, in combination, produce a substantially homogeneous magnetic field in the imaging volume.
  • the variety of magnetic fields across the inward-facing surfaces of the magnets enables production of a substantially homogenous magnetic field that is acceptable for imaging in an imaging volume, and that is of a sufficient size without necessarily resorting to use of very large magnets.
  • the production of a variety of magnetic fields across the inward-facing surfaces of the magnets provide a configuration that enables a more compact magnet assembly for a given imaging volume.
  • MRI Magnetic Resonance Imaging
  • a detector detecting radiofrequency signals emitted by protons within the imaging volume when re-aligning with the substantially homogeneous magnetic field after perturbation, wherein imaging is based on the detected radiofrequency signals.
  • a method of defining a magnetic field for an imaging volume comprising:
  • the target magnetic field is a magnetic field that is acceptably homogeneous
  • the initial model is based on parameters specifying the magnet assembly
  • the modifying comprises modifying one or more parameters representing the surface geometry of one or both inward-facing surfaces of two magnets of the magnet assembly.
  • a computer readable medium having a computer readable program thereon for defining a magnetic field for an imaging volume, the computer program comprising:
  • a magnet assembly comprising:
  • each of the magnets producing a variety of magnetic field strengths across inward-facing surfaces thereof that, in combination, produce a target magnetic field in a target volume.
  • a method of defining a magnetic field for a target volume comprising:
  • a computer readable medium embodying a computer program for defining a magnetic field for a target volume, the computer program comprising:
  • the method described herein can be applied to the computer-based design of magnetic assemblies for use in medical applications, particularly those involving Magnetic Resonance Imaging (MRI) where a bi-planar magnet configuration (eg. Helmholtz type) is to be employed.
  • MRI Magnetic Resonance Imaging
  • bi-planar magnet assemblies include those with spaced-apart first and second pole pieces with generally opposing first and second pole faces, such as, but not limited to, C-shaped magnets, two column magnets, or four column magnets.
  • the method can be utilized to produce magnet assemblies which produce a substantially uniform magnetic field in a particular imaging volume by way of reduction of axisymmetric and/or non-axisymmetric field inhomogeneities.
  • the method described herein may be employed to produce a magnetic field with specially desired characteristics in a particular region within or proximate the magnetic assembly where additional objects or devices may be located whose operation may be affected by the presence and/or characteristics of the magnetic field.
  • objects or devices may be x-ray tubes, medical linear accelerator waveguides (linac), flat-panel imagers, nuclear medicine or ultrasound imagers, or other devices.
  • Such devices may be placed at the ends of the open space between the two poles.
  • the method described herein is also applicable to the definition of a magnetic field in an imaging volume for magnet assemblies that include an opening in one or both of the magnet poles either in the centre or at any location, for positioning of any device at that location.
  • Such placement may be provided for design or operational advantage, such as reduction in size and/or reducing perturbations in patient dosimetry in a treatment system that is integrated with imaging system and/or producing a particular magnetic field.
  • a linear accelerator linac
  • one particular configuration would be the positioning of a linear accelerator (linac) at a location within the magnet structure where the direction of electrons in the waveguide or photons produced by them is parallel to the magnetic field produced by the magnet thus decreasing the subsequent perturbations in patient radiation dosimetry.
  • the magnetic field in the imaging volume may, in certain applications, be a desired though substantially non-homogeneous magnetic field having a particularly desired gradient, for example.
  • the invention may be employed for the defining of magnetic fields in volumes not intended for imaging. For example, it may be desired to define a magnetic field for a volume for directing/guiding/changing the path of an electron or proton beam such as is done currently with the use of bending magnets.
  • magnet assembly and method described herein may be applied in systems that integrate external beam radiotherapy and MRI systems and even such systems configured for use in rotation mode, such as those described in PCT Patent Applications Publication Nos. WO 2007/045076 A1 and WO 2007/045075 A1 both to Fallone et al., the contents of each of which are incorporated herein by reference in their entirety.
  • FIG. 1 is a perspective view of an open compact magnet assembly according to an embodiment
  • FIG. 2 is a cross-sectional view of an open compact magnet assembly of the present invention, including a direct view of the pole assembly surface and the distribution of variable design parameters representing locations on the pole assembly surface;
  • FIG. 3 is a graph plotting the radial position versus the angular position of the variable design parameter distribution of locations on the pole assembly surface
  • FIG. 4 is a perspective view of a contoured non-axisymmetric pole assembly in isolation according to an embodiment
  • FIG. 5 is a perspective view of an alternative open compact magnet assembly, having in particular two large holes vacated through the entire magnet assembly;
  • FIG. 6 is a perspective view of a planar-faced ferromagnetic pole piece in an initial model of a magnet assembly, having a large hole vacated therethrough, along with the distribution of surface locations represented by variable design parameters;
  • FIG. 7 is a perspective view of an axisymmetrically contoured ferromagnetic pole piece resulting from application of the method to the magnet assembly incorporating the pole piece of FIG. 6 ;
  • FIG. 8 is a flowchart showing steps for defining a magnetic field for an imaging volume according to an embodiment
  • FIG. 9 is a flowchart better illustrating the steps for generating an initial model of a magnet assembly as shown in FIG. 8 ;
  • FIG. 10 is a flowchart better illustrating the steps for calculating deviation from a target magnetic field in the form of an objective function as shown in FIG. 8 .
  • FIGS. 1-4 show a magnet assembly 1 according to an embodiment.
  • magnet assembly 1 includes a first ferromagnetic pole assembly 2 and a second ferromagnetic pole assembly 3 .
  • the first and second ferromagnetic pole assemblies 2 , 3 are arranged in a fixed, spaced relationship with one another as “biplanar” magnets thereby to define a space therebetween that encompasses an imaging volume 17 and is large enough to receive an object (not shown) to be imaged at the imaging volume 17 .
  • the magnet assembly 1 is “open” as the object to be imaged can be moved between the pole assemblies 2 , 3 to be positioned at the imaging volume 17 .
  • each of the first and second pole assemblies 2 , 3 comprises both a cylindrical permanent magnet piece 6 ( 7 ) and a substantially cylindrical ferromagnetic piece 8 ( 9 ).
  • the permanent magnet piece 6 ( 7 ) and substantially cylindrical ferromagnetic piece 8 ( 9 ) are arranged such that the ferromagnetic piece 8 ( 9 ) is positioned between the imaging volume 17 and the permanent magnet piece 6 ( 7 ).
  • Inward-facing surfaces, or “pole faces” 4 , 5 are adjacent to the space between the first and second pole assemblies 2 and 3 .
  • each of the first and second ferromagnetic pole assemblies 2 , 3 produce a variety of magnetic field strengths across their inward-facing surfaces 4 , 5 to produce an acceptably homogeneous magnetic field in the imaging volume.
  • an acceptably homogeneous magnetic field is one that comprises about 10 ppm, or less, of magnetic field inhomogeneity. This level of inhomogeneity is considered acceptable for use in Magnetic Resonance Imaging (MRI) devices such as those that base imaging on radio frequency signals emitted by protons and detected by a detector 50 within the imaging volume 17 when re-aligning with the substantially homogeneous magnetic field after perturbation.
  • MRI Magnetic Resonance Imaging
  • the ferromagnetic pieces 8 , 9 are referred to as “substantially” cylindrical as opposed to strictly cylindrical because while the ferromagnetic pieces 8 , 9 are circular when viewed from above (or below) in FIG. 1 , respective inward-facing, or “opposing” surfaces or pole faces 4 , 5 are not strictly planar in this embodiment. Rather, each ferromagnetic piece 8 , 9 is shaped to have a variety of thicknesses of magnetic material (when viewed cross-sectionally) thereby to produce the variety of magnetic field strengths across inward-facing surfaces 4 and 5 .
  • the magnet assembly 1 also includes a yoke structure 10 with first and second yoke plates 11 and 12 connected with four columns 13 - 16 .
  • the first pole assembly 2 is connected to the inward-facing surface of the first yoke plate 11 which is closest to the second yoke plate 12 .
  • the second pole assembly 3 is connected to the inward-facing surface of the second yoke plate 12 .
  • permanent magnet pieces 6 and 7 are formed of a Neodymium-Iron-Boron compound.
  • another material or materials that are permanently magnetized and have a high maximum energy product may be employed.
  • ferromagnetic pieces 8 , 9 and the yoke structure 10 are each formed of iron-bearing material such as steel.
  • Described herein with reference to FIG. 8 is a method for defining a magnetic field for an imaging volume.
  • an initial model of a magnet assembly 1 is generated (step 100 ), and a magnetic field for the imaging volume is determined based on the model (step 200 ).
  • a deviation between the magnetic field and a target magnetic field for the imaging volume is calculated (step 300 ), and the model is updated to reduce the deviation by modifying the magnet assembly 1 to produce a variety of magnetic field strengths that, in combination, produce substantially the target magnetic field in the imaging volume (step 400 ).
  • step 500 If after the updating at step 400 it is determined at that re-iteration is required (step 500 ), the estimating, calculating and updating steps are performed again.
  • the target magnetic field is a homogeneous magnetic field, such that producing substantially the target magnetic field in the imaging volume produces a substantially homogeneous magnetic field in the imaging volume.
  • FIG. 9 shows in further detail the steps for generating an initial model of the magnet assembly 1 , as shown in step 100 , above.
  • a design parameterization for the magnet assembly 1 that defines parameters representing the shape, dimensions and materials of the magnets and of the magnet assembly 1 is selected (step 110 ).
  • Constraints are then defined (step 112 ) such that the parameters are given initial values and designated as either variable or invariable.
  • the initial values of the design parameters may be selected or predefined in any fashion, including empirically, arbitrarily, or randomly, provided they satisfy the specified constraints.
  • the materials of the magnet assembly 1 are defined initially as representing the magnetic properties of steel and Neodymium-Iron-Boron compound as described above but designated as invariable such that during the updating of the model the materials may not be varied.
  • the parameters representing the surface geometry of the inward-facing surfaces of the magnets are defined initially as representing planar or “flat” inward-facing surfaces but are designated as variable such that they may be modified to optimize their shape during the updating to produce non-planar inward-facing surfaces as shown in FIG. 1 .
  • parameter initial values and constraints having been defined thereby to generate the initial model of the magnet assembly (step 114 )
  • the magnetic field produced by the initial magnet assembly, and particularly for the imaging volume of interest is then estimated using a simulation technique employing the finite element method (FEM) or a boundary element method (BEM) (step 300 )
  • FEM finite element method
  • BEM boundary element method
  • the deviation between the target magnetic field and the magnetic field produced by the magnet assembly as represented by the initial model is then calculated.
  • the deviation to be reduced and preferably minimized is defined as an objective function ⁇ (step 310 ), which can be explicitly or implicitly determined by the set of design parameters.
  • ⁇ 1 which in this embodiment is a calculation of the deviation of the actual magnetic field from that of a perfectly homogenous magnetic field over the imaging volume 17 , as shown in Equation (1) below:
  • ⁇ 1 ⁇ ⁇ ⁇ ( B ⁇ ( r ) - B 0 ) 2 ⁇ ⁇ ⁇ ( 1 )
  • B(r) is the magnetic field strength at the location r.
  • B 0 is the desired magnetic field strength.
  • the location of the desired magnetic field strength B 0 is the point of isocenter of the magnet assembly, or at the center point of the imaging volume 17 . In this embodiment, both of these points coincide.
  • the integral in Equation (1) is evaluated over the imaging volume 17 , denoted mathematically as ⁇ .
  • the objective function ⁇ contains at least one term for each of the regions in which the magnetic field is to be defined. In this embodiment, at least one term of the objective function ⁇ is a measure of the deviation of the actual magnetic field from that of a perfectly homogenous magnetic field, calculated over the imaging volume.
  • each region has an associated term that is similarly a measure of the deviation of the actual magnetic field from that which is desired in that region, calculated over the region's associated volume.
  • the other regions denoted as ⁇ i
  • ⁇ i require deviation reduction and the ith term ⁇ i of the objective function ⁇ is calculated as shown in Equation (2), below:
  • ⁇ i ⁇ ⁇ i ⁇ ( B ⁇ ( r ) - B i ⁇ ( r ) ) 2 ⁇ ⁇ ⁇ i ( 2 )
  • B(r) is the magnetic field at the location r
  • B i (r) is the desired magnetic field at the location r.
  • the preferred total objective function ⁇ representing the deviation of the magnetic field estimated to be produced by the magnet assembly 1 from the target magnetic field is calculated simply as a weighted sum of the individual terms (step 312 ), as shown in Equation (3) below:
  • w i is the user-defined weight for the ith term ⁇ i .
  • the weights w i serve to scale the individual terms ⁇ i in the sum according to their importance as determined by the user.
  • the imaging volume 17 center point may be accorded a higher weight than a point coinciding with another object or device (such as a detector 50 or a linear accelerator at some position proximate the magnet assembly 1 ) in order to favour imaging volume homogeneity over interference mitigation.
  • the objective function could include an evaluation of the integrals over the boundaries of the regions denoted ⁇ and ⁇ i above, rather than over the regions themselves.
  • the design vector z k is defined to be the vector whose elements are the individual variable parameters, as shown in Equation (4) below:
  • the inward-facing surfaces are to be contoured in order to reduce the deviation thereby to produce the target magnetic field.
  • the variables used represent respective axial locations of a collection of points 18 on the pole faces 4 and 5 , as shown in FIG. 2 .
  • the locations are measured with respect to a first axis extending generally from the center of the first pole assembly 2 to the center of the second, opposing pole assembly 3 .
  • the points are arranged such that a plot of their radial position versus their angular position, both measured relative to the first axis, forms a two dimensional grid as shown in FIG. 3 .
  • the actual pole faces 4 and 5 are then described by a linear interpolation between the set of the variable parameters that are located on each of the pole faces 4 and 5 .
  • the constraints that these variable parameters are to satisfy are provided in order to ensure a physically reasonable design.
  • preferably such constraints include a range of permissible values of the axial position of the points on the pole faces 4 and 5 , thus enforcing a minimum axial width of the pole assemblies 2 and 3 , as well as a minimum separation between the two opposing pole assemblies 2 and 3 .
  • the pole assemblies 2 and 3 resulting from the above-described parameterization are not necessarily restricted to be axisymmetric.
  • the beneficial reduction of both axisymmetric and non-axisymmetric magnetic field inhomogenieties in the imaging volume 17 is provided, and beneficial tailoring of the magnetic field produced in any region within or proximate the magnet assembly 1 is permitted to accommodate other objects and/or devices that may interfere with the magnetic field or be interfered with by it.
  • the design parameterization described here is presented for the purpose of illustration, as there are many other variations or choices of what parameters are designated as variable and how those parameters relate to the actual geometries they are meant to describe.
  • the collection of points described above may not necessarily actually lie on the surface of the pole faces 4 and 5 , but may rather be weighted control points that are used for some other method of interpolation which defines the actual pole faces 4 and 5 .
  • the number and geometric distribution of the control points may also be chosen in some other way, based on the requirements of the designer.
  • additional design parameters could be designated as variable, such as the location, orientation, or other various dimensions of the pole assemblies 2 and 3 , as well as particular material properties, such as the magnetization distribution of the permanent magnet pieces 6 and 7 .
  • a nonlinear mathematical optimization algorithm is employed in order to adjust each of the variable design parameters to reduce the value of the objective function ⁇ thereby to reduce the deviation. It has been found that the objective function ⁇ is highly nonlinear with respect to the design parameters. As such, a robust nonlinear optimization algorithm is employed in order to achieve convergence within an appropriately prescribed tolerance on a local minimum of the objective function ⁇ within a reasonable number of iterations.
  • the nonlinear optimization algorithm employed is the method of steepest descent.
  • the design vector at the (k+1)th iteration is obtained from the design vector at the kth iteration, as shown in Equation (5) below:
  • ⁇ k is the scalar step size in the search direction vector d k .
  • the step size ⁇ k scales the amount by which the design vector is updated in the search direction at the kth iteration.
  • Step size ⁇ k is determined using an inexact line search algorithm. According to the steepest descent method, the search direction vector d k is defined, as shown in Equation (6) below:
  • ⁇ is the gradient operator
  • ⁇ k is the gradient vector of the objective function with respect to the variable design parameters, evaluated at the kth iteration.
  • Equation (7) The jth element of ⁇ k is calculated, as shown in Equation (7) below:
  • the finite difference approximation includes calculating a difference between the objective function ⁇ for the design where a single variable parameter z kj is perturbed a small finite amount ⁇ z from its normal value at that particular iteration, and the objective function ⁇ for the unperturbed design at that iteration, as shown in Equation (8) below:
  • FIG. 4 shows in isolation the pole assembly 2 of FIG. 1 .
  • a substantially cylindrical shape with a completely flat/planar surface was empirically chosen for the initial model as part of the magnet assembly.
  • the model was updated such that the value for the single-term objective function ⁇ for the magnet assembly 1 was locally minimized and a large, homogenous magnetic field in the imaging volume 17 was obtained.
  • the variable parameters representing locations on the inward-facing surface 4 of ferromagnetic pole piece 8 of pole assembly 2 were modified during the updating from the initial planar configuration to represent a contoured inward-facing surface 4 .
  • the contouring provides varying amounts of magnetic material across the volume of the ferromagnetic pole piece 8 .
  • pole assembly 2 in conjunction with similarly-formed pole assembly 3 produces a variety of magnetic field strengths across its inward-facing surface 4 that combine to produce a substantially homogeneous magnetic field in the imaging volume 17 .
  • the principles set out in the above-described example may be applied to achieve additional objectives, such as for updating the model to incorporate, in addition to the magnet assembly, one or more objects and/or devices capable of disturbing the magnetic field in the imaging volume in a manner that would cause the magnetic field in the imaging volume to be unacceptably inhomogeneous.
  • objects may include physical barriers in a treatment room, one or more devices such as a linear accelerator, an imaging detector or other object, and so forth.
  • the estimating, calculating and updating would be performed based on this updated model.
  • One or more of such devices may also be themselves capable of being disturbed by the magnetic field in the imaging volume in a manner that would cause the one or more devices to operate unacceptably.
  • the method may further include modifying the target magnetic field based on the updated model to, for example, reduce interference of the magnetic field with the one or more devices.
  • Modifications may include modifying the shape of the imaging volume to accommodate proximate devices, or modifying the acceptability threshold of inhomogeneity to accommodate the proximate devices. Such devices may be inserted into the space defined by the magnets, and/or positioned within a hole vacated in one or more of the magnets.
  • the method for defining a magnetic field to incorporate additional objects and/or devices or to incorporate a hole vacated in one or both of the magnets is performed in multiple sequential stages.
  • one or more of the described modifications are incorporated into the design of the magnet assembly obtained from the optimization at the previous stage. Any new associated constraints and additional terms desired in the objective function associated with the newly incorporated modifications are also included and the deviation-reduction method is executed again, resulting in a magnet assembly design for that stage. Multiple stages are executed until all desired modifications have been incorporated into the computer model simulation and a final design is obtained.
  • the modifications may be placed in any particular order within the overall design optimization scheme, and the design parameters designated as variables need not remain the same between different stages.
  • FIGS. 5 to 7 An embodiment of a magnet assembly 19 having two large holes 35 and 36 vacated through the entire magnet assembly 19 is shown in FIGS. 5 to 7 . More particularly, the first and second holes 35 and 36 are vacated from the first and second pole assemblies 20 and 21 , as well as the first and second yoke plates 29 and 30 of the yoke structure 28 , respectively.
  • a different parameterization than that of the previously-described embodiment is employed, wherein an axisymmetric pole assembly is achieved by selecting the design variables to be the axial position of a collection of points 37 that lie along a radial line of the pole assembly surfaces 22 and 23 . This is shown particularly in FIG. 6 .
  • the pole assembly surface 22 is then formed by linearly interpolating the axial position between adjacent points 37 and then constraining all points on the surface 22 that are an equal radial distance from the center of the pole assembly to have an equal axial position.
  • the points 37 designate the height of a series of annular concentric frustoconical segments on the pole assembly surface 22 .
  • the design parameterization in this embodiment may be substituted by other variations or choices as to which parameters are designated as variable, and how such parameters relate to the actual surface geometry.
  • FIG. 7 shows an embodiment of a ferromagnetic pole piece 26 , having been modified during the updating as described above from the planar surface of FIG. 6 to the non-planar/undulating surface shown. More particularly, a substantially cylindrical shape with a completely flat surface was empirically chosen as the initial design for the pole piece and the optimization method was executed to update the design such that the value for the single-term objective function ⁇ for the magnet assembly 19 was locally minimized to obtain a large, homogenous magnetic field in a spherical imaging volume at the magnet assembly isocenter (not shown in the Figures).
  • the method described herein for defining a magnetic field for an imaging volume, and the initial and updated models may be embodied in one or more software applications comprising computer executable instructions executed by the server and other devices.
  • the software application(s) may comprise program modules including routines, programs, object components, data structures etc. and may be embodied as computer readable program code stored on a computer readable medium.
  • the computer readable medium is any data storage device that can store data, which can thereafter be read by a computing device. Examples of computer readable media include for example read-only memory, random-access memory, CD-ROMs, magnetic tape and optical data storage devices.
  • the computer readable program code can also be distributed over a network including coupled computer systems so that the computer readable program code is stored and executed in a distributed fashion.
  • first and second pole assemblies described above may be substituted with, or accompanied by, a coil magnet configuration.
  • optimization parameters varied in the design process to produce the variety of magnetic field strengths could include any combination of the parameters already described herein, as well numerous parameters related to coil magnet design, such as the number of coil turns, the coil current, coil wire gauge, coil shape, and coil location.
  • the estimating, calculating and updating during the above-described method is iteratively performed a threshold number of times, alternatives are possible.
  • the estimating, calculating and updating may be performed iteratively until a magnitude of the deviation represented by the objective function ⁇ falls below a threshold level, or alternatively until the magnitude of the deviation represented by the objective function ⁇ fails to change by more than a threshold amount between successive iterations.
  • the finite difference approximation has been described above for estimating the first derivatives of Equation (7)
  • the first derivatives can alternatively be approximated using more complicated techniques and approximation formulas known to those skilled in the art.
  • One such technique is known as design sensitivity analysis.
  • the target magnetic field for the imaging volume may not be a substantially homogeneous magnetic field, but rather be a nonhomogeneous magnetic field with a specific gradient having a slope and direction that is predefined for a particular application.
  • applications are contemplated in which the target magnetic field is for use not with imaging, but for other functions.
  • One such function is that of directing particles such as electrons, protons or photons emitted by a radiation therapy device.
  • a magnetic field for a target volume for directing/guiding/changing the path of an electron, photon, or proton beam (for proton therapy) in accordance with its energy such as is done currently with the use of bending magnets.
  • Various applications can be served by the method described above in which the two or more magnets of magnet assembly are identical or mirror images of one another, or in which the two or more magnets of the magnet assembly are dissimilar for achieving desired results, such as bending as described above.
  • the magnets may be alike in that they are identical or mirror images of one another, as well as each having planar inward-facing surfaces, in the updated model in accordance with constraints and requirements, the two magnets may result as dissimilar in the sense that they are not exactly alike, in order to achieve bending or a gradient for imaging, etc.
  • the two magnets may be shaped and dimensioned quite different from one another in the updated model so as to achieve the desired results.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • High Energy & Nuclear Physics (AREA)
  • General Engineering & Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Hardware Design (AREA)
  • Evolutionary Computation (AREA)
  • Geometry (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Architecture (AREA)
  • Software Systems (AREA)
US13/000,877 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume Abandoned US20110175694A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US13/000,877 US20110175694A1 (en) 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US12941208P 2008-06-24 2008-06-24
US13/000,877 US20110175694A1 (en) 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume
PCT/CA2009/000860 WO2009155691A1 (en) 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
PCT/CA2009/000860 A-371-Of-International WO2009155691A1 (en) 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US14/174,423 Continuation US9255978B2 (en) 2008-06-24 2014-02-06 Magnetic assembly and method for defining a magnetic field for an imaging volume

Publications (1)

Publication Number Publication Date
US20110175694A1 true US20110175694A1 (en) 2011-07-21

Family

ID=41443936

Family Applications (2)

Application Number Title Priority Date Filing Date
US13/000,877 Abandoned US20110175694A1 (en) 2008-06-24 2009-06-25 Magnetic assembly and method for defining a magnetic field for an imaging volume
US14/174,423 Active 2029-07-27 US9255978B2 (en) 2008-06-24 2014-02-06 Magnetic assembly and method for defining a magnetic field for an imaging volume

Family Applications After (1)

Application Number Title Priority Date Filing Date
US14/174,423 Active 2029-07-27 US9255978B2 (en) 2008-06-24 2014-02-06 Magnetic assembly and method for defining a magnetic field for an imaging volume

Country Status (7)

Country Link
US (2) US20110175694A1 (de)
EP (2) EP2316121A4 (de)
JP (3) JP2011525389A (de)
CN (1) CN102150222B (de)
AU (1) AU2009261901B2 (de)
CA (1) CA2728108C (de)
WO (1) WO2009155691A1 (de)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110137589A1 (en) * 2009-12-02 2011-06-09 Nanalysis Corp. Method and apparatus for producing homogeneous magnetic fields
US20120150500A1 (en) * 2010-12-08 2012-06-14 Fujitsu Limited Optimization processing method and apparatus
US20190011510A1 (en) * 2016-03-22 2019-01-10 Hyperfine Research, Inc. Methods and apparatus for magnetic field shimming
US20190025389A1 (en) * 2016-11-22 2019-01-24 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
WO2019226533A1 (en) * 2018-05-21 2019-11-28 Hyperfine Research, Inc. B0 magnet methods and apparatus for a magnetic resonance imaging system
WO2020050776A1 (en) * 2018-09-03 2020-03-12 Singapore University Of Technology And Design Permanent magnet system and method of forming thereof
US10596393B2 (en) 2012-07-27 2020-03-24 University Health Network Radiotherapy system integrating a radiation source with a magnetic resonance imaging apparatus with movable magnet components
US11105873B2 (en) 2016-11-22 2021-08-31 Hyperfine, Inc. Low-field magnetic resonance imaging methods and apparatus
CN114398803A (zh) * 2022-03-25 2022-04-26 中国科学院深圳先进技术研究院 匀场联合仿真方法、装置、电子设备及存储介质

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106443535B (zh) 2013-05-21 2019-04-23 上海联影医疗科技有限公司 磁共振装置中成像磁场测量和校正的系统
US10393827B2 (en) 2016-06-03 2019-08-27 Texas Tech University System Magnetic field vector imaging array
CN110772280B (zh) * 2018-07-31 2023-05-23 佳能医疗系统株式会社 超声波诊断装置和方法以及图像处理装置和方法
KR102228451B1 (ko) * 2018-12-14 2021-03-17 가천대학교 산학협력단 외부에서 조종 가능한 캡슐형 내시경의 전자기 구동장치를 위한　경사자장 형성코일의 최적화 설계 방법 및 이를 이용한 전자기 구동장치와 그 구동 방법
CN113350699B (zh) * 2021-08-10 2021-10-26 苏州好博医疗器械股份有限公司 一种组合磁场发生装置及其使用方法

Citations (40)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2984782A (en) * 1957-12-11 1961-05-16 Robert H Dicke Spectrum analyzer
US3919678A (en) * 1974-04-01 1975-11-11 Telic Corp Magnetic field generation apparatus
US3924211A (en) * 1968-12-25 1975-12-02 Benyamin Alexandrovich Ioffe Method of orienting electrically conductive bodies, preferably non-magnetic ones, in a magnetic field and apparatus for performing same
US4445102A (en) * 1981-11-19 1984-04-24 The United States Of America As Represented By The United States Department Of Energy Magnet pole tips
US4506240A (en) * 1982-09-01 1985-03-19 Tektronix, Inc. Magnet assembly for a YIG tuned filter having adjustment means to elastically strain a pole piece
US4672346A (en) * 1984-04-11 1987-06-09 Sumotomo Special Metal Co., Ltd. Magnetic field generating device for NMR-CT
US4679022A (en) * 1985-12-27 1987-07-07 Sumitomo Special Metal Co. Ltd. Magnetic field generating device for NMR-CT
US4766378A (en) * 1986-11-28 1988-08-23 Fonar Corporation Nuclear magnetic resonance scanners
US4870380A (en) * 1988-02-26 1989-09-26 Picker International, Ltd. Magnet arrangements
US4943774A (en) * 1989-06-01 1990-07-24 General Atomics Magnetic field control apparatus
US5382905A (en) * 1993-04-01 1995-01-17 Shin-Etsu Chemical Co., Ltd. Magnet apparatus for magnetic resonance imaging
US5436607A (en) * 1992-08-05 1995-07-25 General Electric Company Open (non-enclosed) magnets for magnetic resonance imaging
US5448213A (en) * 1993-09-16 1995-09-05 Northrup Grumman Corporation Electromagnetic shielding concept for superconducting levitating magnets
US5539366A (en) * 1994-07-27 1996-07-23 General Electric Company Magnet having contoured pole faces for magnetic field homogeneity
US5684399A (en) * 1994-07-06 1997-11-04 The Petroleum Science And Technology Institute Detection of magnetized fluid flows
US6011396A (en) * 1998-01-02 2000-01-04 General Electric Company Adjustable interventional magnetic resonance imaging magnet
US6020805A (en) * 1997-04-12 2000-02-01 Seas Fabrikker As Permanent magnet assembly
US6198286B1 (en) * 1998-05-11 2001-03-06 Esaote S.P.A. Magnet structure, particularly for nuclear magnetic resonance imaging machines
US6335670B1 (en) * 2000-04-14 2002-01-01 Marconi Medical Systems Finland, Inc. Mri system with split rose ring with high homogeneity
US6340888B1 (en) * 1998-09-02 2002-01-22 Sumitomo Special Metals Co., Ltd. Magnetic field generator for MRI
US20020097122A1 (en) * 2001-01-25 2002-07-25 Uri Rapoport Field adjusting mechanisms and methods for permanent magnet arrangement with backplate
US20030011455A1 (en) * 2001-07-16 2003-01-16 Hitachi, Ltd. Magnet, a method of adjustment of magnetic field and a magnetic resonance imaging apparatus
US20030011456A1 (en) * 2001-05-17 2003-01-16 Mitsubishi Denki Kabushiki Kaisha Superconductive magnet device
US20030048163A1 (en) * 2001-09-12 2003-03-13 Hiroyuki Watanabe Superconducting magnet and magnetic resonance imaging apparatus using the same
US6535092B1 (en) * 1999-09-21 2003-03-18 Magnetic Solutions (Holdings) Limited Device for generating a variable magnetic field
US6570475B1 (en) * 2000-11-20 2003-05-27 Intermagnetics General Corp. Split type magnetic resonance imaging magnet
US6642826B1 (en) * 2000-08-09 2003-11-04 Sumitomo Special Metals Co., Ltd. Magnetic field generator and assembling method thereof
US20050052266A1 (en) * 2003-09-10 2005-03-10 Shin-Etsu Chemical Co., Ltd. Packaging plate for magnetic circuit, method for packaging magnetic circuit using the same, and magnetic circuit package
US20050068138A1 (en) * 2003-09-29 2005-03-31 General Electric Company Multiple ring polefaceless permanent magnet and method of making
US6897751B2 (en) * 1999-11-16 2005-05-24 Neomax Co., Ltd. Pole-piece unit, method for assembling the same, and magnetic field generator
US7071694B1 (en) * 1999-10-29 2006-07-04 Oxford Magnet Technology Limited Magnet assembly of an MRI system with concentric annular ferromagnetic laminations
GB2425842A (en) * 2005-05-05 2006-11-08 Plant Bioscience Ltd Magnetic resonance sensor with rotatable magnetic rods placed around the sample
US7143507B2 (en) * 1999-07-15 2006-12-05 Neomax Co., Ltd. Recycling method for magnetic field generator
US7463129B1 (en) * 2000-11-22 2008-12-09 Fonar Corporation Magnet structure
US7479859B2 (en) * 2006-03-08 2009-01-20 Jack Gerber Apparatus and method for processing material in a magnetic vortex
US20090231073A1 (en) * 2005-09-30 2009-09-17 Hitachi Metals, Ltd. Magnetic Field Control Method and Magnetic Field Generator
US7667462B2 (en) * 2006-12-22 2010-02-23 Schlumberger Technology Corporation Nuclear magnetic resonance module
US7706858B1 (en) * 2003-05-09 2010-04-27 Fonar Corporation Head and neck immobilization in magnetic resonance imaging
US7796002B2 (en) * 2004-09-30 2010-09-14 Hitachi Metals, Ltd. Magnetic field generator for MRI
US7928730B2 (en) * 2006-01-23 2011-04-19 Hitachi, Ltd. Electromagnet apparatus generating a homogeneous magnetic field with ferromagnetic members arranged inside cryogenic vessels

Family Cites Families (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55154046A (en) * 1979-05-17 1980-12-01 Sanyo Electric Co Ltd Convergence device
DE3779715T2 (de) * 1986-09-27 1993-01-28 Sumitomo Spec Metals Vorrichtung zur erzeugung eines magnetfeldes fuer rechnergesteuerte tomographie mittels magnetischer kernresonanz.
JPH03273603A (ja) * 1990-03-23 1991-12-04 Seiko Epson Corp 磁界発生装置
DE4210217C2 (de) * 1992-03-28 1994-03-24 Bruker Analytische Messtechnik Verfahren zum Bau einer optimierten Magnetspulenanordnung
US5382904A (en) * 1992-04-15 1995-01-17 Houston Advanced Research Center Structured coil electromagnets for magnetic resonance imaging and method for fabricating the same
GB2276945B (en) * 1993-04-08 1997-02-26 Oxford Magnet Tech Improvements in or relating to MRI magnets
US6150911A (en) * 1996-07-24 2000-11-21 Odin Technologies Ltd. Yoked permanent magnet assemblies for use in medical applications
US6218838B1 (en) * 1998-08-28 2001-04-17 Picker International, Inc. MRI magnet with high homogeneity, patient access, and low forces on the driver coils
US6150819A (en) * 1998-11-24 2000-11-21 General Electric Company Laminate tiles for an MRI system and method and apparatus for manufacturing the laminate tiles
US6172588B1 (en) * 1999-04-23 2001-01-09 General Electric Company Apparatus and method for a superconductive magnet with pole piece
JP2002336215A (ja) * 2001-05-17 2002-11-26 Mitsubishi Electric Corp 超電導マグネット装置及び磁場均一度調整方法
JP4040334B2 (ja) * 2002-03-14 2008-01-30 株式会社日立メディコ 磁気共鳴イメージング装置
US6707363B1 (en) * 2003-01-06 2004-03-16 Brk Wireless Company, Inc. NMR head imaging system
JP2004236747A (ja) * 2003-02-04 2004-08-26 Hitachi Medical Corp 開放型磁気共鳴イメージング装置用磁石
US7148689B2 (en) * 2003-09-29 2006-12-12 General Electric Company Permanent magnet assembly with movable permanent body for main magnetic field adjustable
JP2005118098A (ja) * 2003-10-14 2005-05-12 Hitachi Medical Corp 磁気共鳴イメージング装置
US7019609B2 (en) * 2004-06-21 2006-03-28 General Electric Company Magnetic field generating device and method of shimming thereof
JP2007037835A (ja) * 2005-08-04 2007-02-15 Hitachi Medical Corp 磁気共鳴イメージング装置
WO2007045075A1 (en) 2005-10-17 2007-04-26 Alberta Cancer Board Real-time dose reconstruction using dynamic simulation and image guided adaptive radiotherapy
ES2383983T3 (es) * 2005-10-17 2012-06-28 Alberta Health Services Sistema de radioterapia de haz externo e IRM integrado

Patent Citations (40)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2984782A (en) * 1957-12-11 1961-05-16 Robert H Dicke Spectrum analyzer
US3924211A (en) * 1968-12-25 1975-12-02 Benyamin Alexandrovich Ioffe Method of orienting electrically conductive bodies, preferably non-magnetic ones, in a magnetic field and apparatus for performing same
US3919678A (en) * 1974-04-01 1975-11-11 Telic Corp Magnetic field generation apparatus
US4445102A (en) * 1981-11-19 1984-04-24 The United States Of America As Represented By The United States Department Of Energy Magnet pole tips
US4506240A (en) * 1982-09-01 1985-03-19 Tektronix, Inc. Magnet assembly for a YIG tuned filter having adjustment means to elastically strain a pole piece
US4672346A (en) * 1984-04-11 1987-06-09 Sumotomo Special Metal Co., Ltd. Magnetic field generating device for NMR-CT
US4679022A (en) * 1985-12-27 1987-07-07 Sumitomo Special Metal Co. Ltd. Magnetic field generating device for NMR-CT
US4766378A (en) * 1986-11-28 1988-08-23 Fonar Corporation Nuclear magnetic resonance scanners
US4870380A (en) * 1988-02-26 1989-09-26 Picker International, Ltd. Magnet arrangements
US4943774A (en) * 1989-06-01 1990-07-24 General Atomics Magnetic field control apparatus
US5436607A (en) * 1992-08-05 1995-07-25 General Electric Company Open (non-enclosed) magnets for magnetic resonance imaging
US5382905A (en) * 1993-04-01 1995-01-17 Shin-Etsu Chemical Co., Ltd. Magnet apparatus for magnetic resonance imaging
US5448213A (en) * 1993-09-16 1995-09-05 Northrup Grumman Corporation Electromagnetic shielding concept for superconducting levitating magnets
US5684399A (en) * 1994-07-06 1997-11-04 The Petroleum Science And Technology Institute Detection of magnetized fluid flows
US5539366A (en) * 1994-07-27 1996-07-23 General Electric Company Magnet having contoured pole faces for magnetic field homogeneity
US6020805A (en) * 1997-04-12 2000-02-01 Seas Fabrikker As Permanent magnet assembly
US6011396A (en) * 1998-01-02 2000-01-04 General Electric Company Adjustable interventional magnetic resonance imaging magnet
US6198286B1 (en) * 1998-05-11 2001-03-06 Esaote S.P.A. Magnet structure, particularly for nuclear magnetic resonance imaging machines
US6340888B1 (en) * 1998-09-02 2002-01-22 Sumitomo Special Metals Co., Ltd. Magnetic field generator for MRI
US7143507B2 (en) * 1999-07-15 2006-12-05 Neomax Co., Ltd. Recycling method for magnetic field generator
US6535092B1 (en) * 1999-09-21 2003-03-18 Magnetic Solutions (Holdings) Limited Device for generating a variable magnetic field
US7071694B1 (en) * 1999-10-29 2006-07-04 Oxford Magnet Technology Limited Magnet assembly of an MRI system with concentric annular ferromagnetic laminations
US6897751B2 (en) * 1999-11-16 2005-05-24 Neomax Co., Ltd. Pole-piece unit, method for assembling the same, and magnetic field generator
US6335670B1 (en) * 2000-04-14 2002-01-01 Marconi Medical Systems Finland, Inc. Mri system with split rose ring with high homogeneity
US6642826B1 (en) * 2000-08-09 2003-11-04 Sumitomo Special Metals Co., Ltd. Magnetic field generator and assembling method thereof
US6570475B1 (en) * 2000-11-20 2003-05-27 Intermagnetics General Corp. Split type magnetic resonance imaging magnet
US7463129B1 (en) * 2000-11-22 2008-12-09 Fonar Corporation Magnet structure
US20020097122A1 (en) * 2001-01-25 2002-07-25 Uri Rapoport Field adjusting mechanisms and methods for permanent magnet arrangement with backplate
US20030011456A1 (en) * 2001-05-17 2003-01-16 Mitsubishi Denki Kabushiki Kaisha Superconductive magnet device
US20030011455A1 (en) * 2001-07-16 2003-01-16 Hitachi, Ltd. Magnet, a method of adjustment of magnetic field and a magnetic resonance imaging apparatus
US20030048163A1 (en) * 2001-09-12 2003-03-13 Hiroyuki Watanabe Superconducting magnet and magnetic resonance imaging apparatus using the same
US7706858B1 (en) * 2003-05-09 2010-04-27 Fonar Corporation Head and neck immobilization in magnetic resonance imaging
US20050052266A1 (en) * 2003-09-10 2005-03-10 Shin-Etsu Chemical Co., Ltd. Packaging plate for magnetic circuit, method for packaging magnetic circuit using the same, and magnetic circuit package
US20050068138A1 (en) * 2003-09-29 2005-03-31 General Electric Company Multiple ring polefaceless permanent magnet and method of making
US7796002B2 (en) * 2004-09-30 2010-09-14 Hitachi Metals, Ltd. Magnetic field generator for MRI
GB2425842A (en) * 2005-05-05 2006-11-08 Plant Bioscience Ltd Magnetic resonance sensor with rotatable magnetic rods placed around the sample
US20090231073A1 (en) * 2005-09-30 2009-09-17 Hitachi Metals, Ltd. Magnetic Field Control Method and Magnetic Field Generator
US7928730B2 (en) * 2006-01-23 2011-04-19 Hitachi, Ltd. Electromagnet apparatus generating a homogeneous magnetic field with ferromagnetic members arranged inside cryogenic vessels
US7479859B2 (en) * 2006-03-08 2009-01-20 Jack Gerber Apparatus and method for processing material in a magnetic vortex
US7667462B2 (en) * 2006-12-22 2010-02-23 Schlumberger Technology Corporation Nuclear magnetic resonance module

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8712706B2 (en) * 2009-12-02 2014-04-29 Nanalysis Corp. Method and apparatus for producing homogeneous magnetic fields
US20110137589A1 (en) * 2009-12-02 2011-06-09 Nanalysis Corp. Method and apparatus for producing homogeneous magnetic fields
US20120150500A1 (en) * 2010-12-08 2012-06-14 Fujitsu Limited Optimization processing method and apparatus
US8577653B2 (en) * 2010-12-08 2013-11-05 Fujitsu Limited Optimization processing method and apparatus
US10596393B2 (en) 2012-07-27 2020-03-24 University Health Network Radiotherapy system integrating a radiation source with a magnetic resonance imaging apparatus with movable magnet components
US20190011510A1 (en) * 2016-03-22 2019-01-10 Hyperfine Research, Inc. Methods and apparatus for magnetic field shimming
US11740302B2 (en) 2016-03-22 2023-08-29 Hyperfine Operations, Inc. Methods and apparatus for magnetic field shimming
US11294006B2 (en) 2016-03-22 2022-04-05 Hyperfine Operations, Inc. Methods and apparatus for magnetic field shimming
US10794974B2 (en) 2016-03-22 2020-10-06 Hyperfine Research, Inc. Methods and apparatus for magnetic field shimming
US10788550B2 (en) * 2016-03-22 2020-09-29 Hyperfine Research, Inc. Methods and apparatus for magnetic field shimming
US10613168B2 (en) 2016-03-22 2020-04-07 Hyperfine Research, Inc. Methods and apparatus for magnetic field shimming
US10310037B2 (en) * 2016-11-22 2019-06-04 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
US20190025389A1 (en) * 2016-11-22 2019-01-24 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
US10698048B2 (en) 2016-11-22 2020-06-30 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
US10585153B2 (en) 2016-11-22 2020-03-10 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
US10527692B2 (en) 2016-11-22 2020-01-07 Hyperfine Research, Inc. Rotatable magnet methods and apparatus for a magnetic resonance imaging system
US11105873B2 (en) 2016-11-22 2021-08-31 Hyperfine, Inc. Low-field magnetic resonance imaging methods and apparatus
US11119168B2 (en) 2016-11-22 2021-09-14 Hyperfine, Inc. Low-field magnetic resonance imaging methods and apparatus
US11841408B2 (en) 2016-11-22 2023-12-12 Hyperfine Operations, Inc. Electromagnetic shielding for magnetic resonance imaging methods and apparatus
TWI743481B (zh) * 2018-05-21 2021-10-21 美商海珀菲纳股份有限公司 用於磁共振成像系統的b磁鐵方法及設備
WO2019226533A1 (en) * 2018-05-21 2019-11-28 Hyperfine Research, Inc. B0 magnet methods and apparatus for a magnetic resonance imaging system
US11726155B2 (en) 2018-05-21 2023-08-15 Hyperfine Operations, Inc. B0 magnet methods and apparatus for a magnetic resonance imaging system
US11215685B2 (en) 2018-05-21 2022-01-04 Hyperfine, Inc. B0 magnet methods and apparatus for a magnetic resonance imaging system
US11448715B2 (en) * 2018-09-03 2022-09-20 Singapore University Of Technology And Design Permanent magnet system and method of forming thereof
WO2020050776A1 (en) * 2018-09-03 2020-03-12 Singapore University Of Technology And Design Permanent magnet system and method of forming thereof
CN114398803A (zh) * 2022-03-25 2022-04-26 中国科学院深圳先进技术研究院 匀场联合仿真方法、装置、电子设备及存储介质

Also Published As

Publication number Publication date
AU2009261901A1 (en) 2009-12-30
EP2511724B1 (de) 2019-03-13
CA2728108C (en) 2016-09-27
JP2011525389A (ja) 2011-09-22
EP2316121A4 (de) 2012-01-11
AU2009261901B2 (en) 2014-07-31
US9255978B2 (en) 2016-02-09
US20140229141A1 (en) 2014-08-14
CA2728108A1 (en) 2009-12-30
JP2015116491A (ja) 2015-06-25
WO2009155691A1 (en) 2009-12-30
CN102150222B (zh) 2014-05-28
WO2009155691A8 (en) 2011-07-14
EP2511724A1 (de) 2012-10-17
CN102150222A (zh) 2011-08-10
EP2316121A1 (de) 2011-05-04
JP2017104568A (ja) 2017-06-15

Similar Documents

Publication Publication Date Title
US9255978B2 (en) Magnetic assembly and method for defining a magnetic field for an imaging volume
Stanescu et al. Characterization of tissue magnetic susceptibility‐induced distortions for MRIgRT
US20100164494A1 (en) Transmit profile control in mri
van Gemert et al. High‐permittivity pad design tool for 7T neuroimaging and 3T body imaging
US7196603B2 (en) Magnetic coil design using optimization of sinusoidal coefficients
Santos et al. Magnetic shielding investigation for a 6 MV in‐line linac within the parallel configuration of a linac‐MR system
US20180011156A1 (en) Multi-purpose gradient array for magnetic resonance imaging
US20110254545A1 (en) Method and device for determining a magnetic resonance system control sequence
Chen et al. Electromagnetic computation and modeling in MRI
Fiedler et al. Performance analysis of integrated RF microstrip transmit antenna arrays with high channel count for body imaging at 7 T
US11740301B2 (en) Eigenmode transmit array coil for magnetic resonance imaging
Siebold Design optimization of main, gradient and RF field coils for MR imaging
EP2677333B1 (de) Verfahren zur Korrektur der Inhomogenität des statischen Magnetfeldes einer Vorrichtung zur MR-Bildgebung
US11353535B2 (en) Reduction of artifacts in magnetic resonance imaging
JP7013440B2 (ja) Ｍｒｉシステムの勾配コイルデバイス又は別の周期的に応力がかけられるデバイスを作動させる方法及び制御ユニット
US6717409B2 (en) Method for calculating conductor paths in a switched gradient coil system, and magnetic resonance tomography apparatus employing such a switched gradient coil system
WO2016133204A1 (ja) 磁場調整支援システムおよび磁場調整方法
US20130257430A1 (en) Controlling Magnetic Resonance Systems
Lotey et al. Evaluation of an MRI linac magnetic isocenter walkout with gantry rotation in the presence of angle-specific corrections
JP4566024B2 (ja) 磁気共鳴イメージング装置
JP5149004B2 (ja) 磁気共鳴イメージング装置
Kassahun et al. A power efficient actively shielded two-channel transverse MRI gradient coil numerical design
Harris et al. Design study to investigate the effect of curvature on gradient coil performance for localized regions of interest
JPH0515507A (ja) 均一磁場コイル

Legal Events

Date Code Title Description
AS Assignment

Owner name: ALBERTA CANCER BOARD, CANADA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FALLONE, GINO B.;TADIC, TONY;MURRAY, BRAD;REEL/FRAME:025765/0098

Effective date: 20080911

Owner name: ALBERTA HEALTH SERVICES, CANADA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ALBERTA CANCER BOARD;REEL/FRAME:025765/0219

Effective date: 20090319

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION