WO2008100546A1 - Contrôle de profil de transmission en irm - Google Patents

Contrôle de profil de transmission en irm Download PDF

Info

Publication number
WO2008100546A1
WO2008100546A1 PCT/US2008/001911 US2008001911W WO2008100546A1 WO 2008100546 A1 WO2008100546 A1 WO 2008100546A1 US 2008001911 W US2008001911 W US 2008001911W WO 2008100546 A1 WO2008100546 A1 WO 2008100546A1
Authority
WO
WIPO (PCT)
Prior art keywords
coil
magnetic field
coils
resonance imaging
magnetic resonance
Prior art date
Application number
PCT/US2008/001911
Other languages
English (en)
Inventor
Alan P. Koretsky
Jeff H. Duyn
Shumin Wang
Hellmut Merkle
Original Assignee
The Government Of The United States Of America, As Represented By The Secretary, Department Of Health And Human Services
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 The Government Of The United States Of America, As Represented By The Secretary, Department Of Health And Human Services filed Critical The Government Of The United States Of America, As Represented By The Secretary, Department Of Health And Human Services
Priority to US12/449,514 priority Critical patent/US8125225B2/en
Publication of WO2008100546A1 publication Critical patent/WO2008100546A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
    • G01R33/3415—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with flexible receiver channels
    • 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
    • G01R33/24—Arrangements or instruments for measuring magnetic variables involving magnetic resonance for measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/246—Spatial mapping of the RF magnetic field B1
    • 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
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
    • G01R33/365—Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array
    • 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
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5611—Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE
    • G01R33/5612—Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels
    • 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
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/5659—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field

Definitions

  • MRI magnetic resonance imaging
  • RF radio frequency
  • RF coils are used for transmit and receive modes.
  • RF coils In the transmit mode, RF coils generate a B 1 magnetic field that excites nuclear spins from low-energy states to high-energy states at the corresponding Larmor Frequency.
  • the same set or a different set of RF coils detect the echo generated by nuclear spins that transit from high-energy states to low-energy states.
  • RF coils In the transmit mode, RF coils are expected to provide the desired excitation, e.g., a Bi magnetic field profile for a given imaging method.
  • main B 0 magnetic fields such as at approximately 3 Tesla or higher.
  • the resonant or Larmor frequency of 1 H shifts into the very high frequency (VHF) or ultra high frequency (UHF) domain.
  • Electrodynamic material properties of the imaged subject such as electric conductivity and dielectric permittivity increasingly distort the transmitted B 1 magnetic field. These distortions are typically subject-dependent, and may also depend upon the positioning of the imaging subject, the region of interest and distribution of macroscopic fractions with different electrodynamic material properties within the subject that is being imaged. For example, dynamic reordering/redistribution of dielectric properties (heart/lung placement, -size, - shape) may occur which needs to be addressed within the whole body in vivo investigation.
  • the axial dimension of the region of interest is comparable to or larger than a wavelength.
  • the sinusoidal or the co- sinusoidal current distribution provided by the first Fourier mode does not generate a homogeneous field inside such a finite-length ROI.
  • the phase variation in the transverse dimension becomes large and hot spots appear at the phantom center due to the so-called dielectric resonance effect.
  • B 1 magnetic field Another approach to improve the homogeneity of B 1 magnetic field is to actively control the phase and magnitude of the transmit signal, for example, with a phased- array transmit coil.
  • phase and magnitude of the transmit signal for example, with a phased- array transmit coil.
  • B 1 homogeneity may only be optimally achievable on one axial slice for one phase-magnitude configuration.
  • Another approach to improve the homogeneity Of B 1 magnetic field is to use shimming by inserting high-permittivity material. More specifically, for non traveling-wave coils, where subjects are treated as dielectric resonators, the equivalent ROI radius is increased by inserting high-permittivity material; thus, the Bi magnetic field homogeneity is accordingly improved.
  • the localized Bi magnetic field excitations have the advantage of reduced specific absorption rate (SAR) and thus improved patient safety.
  • SAR specific absorption rate
  • ASL arterial spin labeled
  • RF coils are used to saturate the proton spins in the common carotid arterial.
  • spins in a specific region are selectively excited.
  • One embodiment includes a magnetic resonance imaging apparatus, comprising: a main magnet to generate a substantially uniform main B 0 magnetic field through an examination region; a coil system including a first coil layer and a second coil layer disposed substantially parallel to the first coil layer with a defined air gap in a radial direction, the first coil layer including a first coil array, the second coil layer including a second coil array, the first and second coil arrays being coupled and cooperating to selectively produce a prespecified Bi magnetic field within the examination region.
  • a magnetic resonance imaging method comprising: generating a substantially uniform main B 0 magnetic field through an examination region; and generating a prespecified B 1 magnetic field within the examination region.
  • One embodiment includes a coil arrangement, comprising: a first coil layer including a first coil array; and a second coil layer including a second coil array, the second coil layer being disposed substantially parallel to the first coil layer with a defined air gap in a radial direction, the first and second coil arrays being coupled and cooperating to selectively produce a prespecified B 1 magnetic field within an examination region.
  • FIGURE IA diagrammatically illustrates an exemplary magnetic resonance imaging system according to an exemplary embodiment of the invention
  • FIGURE IB diagrammatically illustrates an exemplary coil arrangement according to an exemplary embodiment of the invention
  • FIGURE 1C diagrammatically illustrates an exemplary magnetic resonance imaging system according to an exemplary embodiment of the invention
  • FIGURE 2A diagrammatically illustrates an exemplary coil arrangement according to an exemplary embodiment of the invention
  • FIGURE 2B illustrates an exemplary flow chart for coupling optimization according to an exemplary embodiment of the invention
  • FIGURE 3A illustrates an exemplary Bi magnetic field map
  • FIGURE 3B illustrates an exemplary B 1 magnetic field map of FIGURE 3 A corrected with a single inner layer coil according to an exemplary embodiment of the invention
  • FIGURE 4 illustrates an exemplary B, magnetic field map of FIGURE 3 A corrected with an exemplary eight element inner coil array according to an exemplary embodiment of the invention.
  • FIGURE 5 illustrates exemplary optimization results of a single coil element of FIGURE 3B according to an exemplary embodiment of the invention.
  • a magnetic resonance imaging scanner or system 100 may include a housing 102 defining a generally cylindrical scanner bore 104 defining an examination region 105, inside of which an associated imaging subject 106 is disposed.
  • the housing 102 is shown in cross-section to illustrate the inside of the housing 102.
  • Main magnetic field coils 110 may be disposed inside the housing 102, and may produce a main B 0 magnetic field parallel to a central axis 112 of the scanner bore 104.
  • the direction of the main B 0 magnetic field is parallel to the z-axis of the reference x-y-z Cartesian coordinate system.
  • Main magnetic field coils 110 are typically superconducting coils disposed inside cryoshrouding 114, although resistive main magnets may also be used.
  • the main magnetic field coils 110 may generate the main B 0 magnetic field, at approximately 3 Tesla or higher, which may be substantially uniform in an imaging volume of the bore 104.
  • the housing 102 also houses or supports magnetic field gradient coil(s) 116 for selectively producing known magnetic field gradients parallel to the central axis 112 of the bore 104, along in-plane directions transverse to the central axis 112, or along other selected directions.
  • the gradient coil(s) 116 are shielded with shielding coil(s) (not shown).
  • the shielding coils are designed to cooperate with the gradient coil 116 to generate a magnetic field which has a substantially zero magnetic flux density outside an area defined by the outer radius of the shielding coil(s).
  • the magnetic resonance imaging scanner 100 may include a radio frequency coil arrangement or system 122 to selectively excite and/or detect magnetic resonances.
  • the radio frequency coil arrangement 122 is disposed inside the bore 104 and may include first or outer coil layer 124 and second or inner coil layer 126 extending substantially parallel to one another with a defined air gap in a radial direction y. Although only one inner coil layer 126 is illustrated, a number of inner coil layers may be, for example, two, three, four,..., ten or more layers, disposed substantially parallel to one another with defined air gaps in the radial direction y.
  • the outer coil layer 124 includes one or more outer layer coil arrays 128 surrounded by a shield 129. Each outer layer coil array 128 may include a plurality of coil elements or coils 132.
  • the inner coil layer 126 includes one or more coil arrays 130 including a plurality of coil elements or coils 134.
  • the coil arrangement 122 may be used to image a brain (as illustrated), a heart, a leg, a body part, or the like.
  • the coil arrays 128, 130 of the outer and inner coil layers 124, 126 cooperate to transmit a selected B 1 magnetic field, such as, for example, a uniform Bi magnetic field or a non-uniform Bi magnetic field.
  • the inner coil layer 126 may include receive coils or elements. Alternatively, the magnetic resonances may be both excited and received by a single coil array, such as, for example, by the outer layer coil array 128. It will be appreciated that if the outer layer coil array 128 is used for both transmitting and receiving, then the inner layer coil array 130 is optionally omitted.
  • An MRI controller 140 operates magnetic field gradient controller or controllers 142 and a radio frequency transmitter or transmitters 144 coupled to the outer layer coil array 128 to selectively energize the outer layer radio frequency coil array 128.
  • a baseline, primary or first Bj 1 magnetic field may be generated.
  • a secondary or second B 1 magnetic field, generated by the inner coil array 130 may be superimposed on the baseline Bi 1 magnetic field to provide the B 1 magnetic field of a desired profile.
  • the outer layer coil array 128 is quadrature driven.
  • Magnetic resonance is generated and spatially encoded in at least a portion of a region of interest of the imaging subject 106.
  • a selected k-space trajectory is traversed, such as a Cartesian trajectory, a plurality of radial trajectories, or a spiral trajectory.
  • imaging data may be acquired as projections along selected magnetic field gradient directions.
  • a radio frequency receiver or receivers 146 coupled to the receive elements or the coil array 128 may acquire magnetic resonance samples that are stored in a magnetic resonance data memory 150.
  • the imaging data may be reconstructed by a reconstruction processor 152 into an image representation.
  • a reconstruction processor 152 In the case of Cartesian k-space sampled data or other data resampled appropriately, a Fourier transform-based reconstruction algorithm may be employed. Other reconstruction algorithms, such as, for example, a filtered backprojection- based reconstruction, may also be used depending upon the format of the acquired magnetic resonance imaging data.
  • SENSE sensitivity encoding
  • the reconstruction processor 152 reconstructs folded images from the imaging data acquired by each RF coil and combines the folded images along with coil sensitivity parameters to produce an unfolded reconstructed image.
  • the reconstructed image generated by the reconstruction processor 152 may be stored in an image memory 154, and may be displayed on a user interface 156, stored in non-volatile memory, transmitted over a local intranet or the Internet, viewed, stored, manipulated, or so forth.
  • the user interface 156 may also enable a radiologist, technician, or other operator of the magnetic resonance imaging scanner 100 to communicate with the magnetic resonance imaging controller 140 to select, modify, and execute magnetic resonance imaging sequences.
  • the coil array 128 of the outer coil layer 124 is actively driven and may include any typical coil structure that radiates the baseline B 1 1 magnetic field.
  • An example of the coil array 128 of the outer coil layer 124 includes a conventional birdcage coil array 128 including parallel coil elements or rods 132. Of course, it is contemplated that the coil array 128 of the outer coil layer 124 may include surface coils or saddle coils.
  • the coil array 130 of the inner coil layer 126 may be coupled to the coil array
  • the coils 134 of the inner coil layer 126 interact with the baseline Bi' magnetic field differently at different azimuthal locations.
  • the inner coil layer 126 includes azimuthally distributed surface coils 134. In the distributed coils arrangement, the distributed coils are positioned spaced over a surface so that a sum of centroid positions represents the desired harmonic. Distributed coils may assist in correcting patient induced inhomogeneity of the B 1 magnetic field.
  • At least one of the outer or inner coil layer 124, 126 includes an array of surface coils.
  • the coil elements 132, 134 of the outer and inner coil layers 124, 126 may include electrical and/or magnetic dipoles, e.g., strip-lines and/or loop coils.
  • the pattern for the coils may be selected based on the design considerations.
  • the examples of the layouts for the loop coils include overlapped loop coils, gapped loop coils, and touched neighboring loop coils.
  • any number of coil arrays 128, 130 with any number of coil elements 132, 134 may be used.
  • a single coil array 130 may be used in the inner coil layer 126.
  • increasing the number of coil arrays 130 and/or coil elements 134 of the inner coil layer 126 introduces more degrees of freedom that may be engineered to achieve a globally homogenized Bi magnetic field profile or an arbitrary in- homogeneous Bi magnetic field profile.
  • a single inner layer coil array 130 including eight coil elements 134 is shown for illustrative purposes.
  • the coil arrays 130 of the inner coil layer 126 may be disposed on a former
  • the former may be disposed with a defined air gap from the imaging subject 106.
  • the air gap is selected for maximum patient comfort and allows for installation of the electronics, such as a separate MRI receive coil array.
  • the air gap can not be selected too great as the electromagnetic fields re-radiated from the coil array 130 of the inner layer 126 may decay rapidly in the vicinity of inner coil layer 126 resulting in the magnetic field patterns which are less azimuthally distinguishable. [00036] Besides choosing the appropriate type, number and layout of the inner layer coil elements 134, another consideration is selective modification of the magnitude and/or the phase of the Bj 11 secondary magnetic field.
  • a loop coil may be viewed in a simplified circuit model as a series
  • the induced coil currents intensity is proportional to the electro-dynamic voltage and inverse proportional to the series RLC network impedance.
  • the voltage is provided by the baseline electromagnetic field according to Faraday's law, which states that the electro-dynamic voltage is proportional to the rate of the magnetic flux changes with respect to time.
  • the magnetic flux is proportional to the magnetic field strength, e.g., B field, and the projection of the area of a loop coil on the direction of the B field.
  • the secondary B 1 11 magnetic field may be modified by changing the RLC network impedance.
  • the secondary B 1 11 magnetic field may be modified by using resistive attenuation, frequency detuning, a combination of the resistive attenuation and frequency detuning, or angled positioning with respect to the outer layer transmit coil.
  • Resistive attenuation may be achieved by connecting resistive components in series to the inner layer coil 134. This corresponds to increasing the resistance R in the coil system 122. Thus, the induced current density decreases.
  • each inner layer coil 134 is individually tuned to a frequency different from the Larmor frequency, e.g., the resonant frequency of the outer layer coil array 128, by using at least one of capacitors, inductors, or a combination of the capacitors and inductors.
  • Each method corresponds to changing the capacitance C, the inductance L, or both the capacitance C and inductance L in the coil system 122.
  • the frequency detuning is achieved by using capacitors available in the loop coil design.
  • the impedance of a coil element achieves its minimum at the resonance frequency, frequency detuning increases the coil impedance when imaging at the Larmor frequency. The induced current intensity is reduced.
  • the detuning capacitors and inductors are used to afford more freedom in design.
  • the resistance or capacitance is changed remotely so that the amount of coupling is optimized for each individual sample, for example, different imaging subjects 106.
  • a loop coil tuned at the Larmor frequency is used as the reference. Applying extra capacitance to detune the coil is equivalent to a geometrical change of decreasing the circumference of the loop coil. On the other hand, applying extra inductance to detune the coil is equivalent to a geometrical change of increasing the circumference of the loop coil. Thus, the geometrical features or their equivalents may be changed to control the induced current intensity.
  • each inner layer coil 134 produces a magnetic field distribution within the bore 104.
  • an inner layer coil currents processor 170 may determine appropriate currents for one or more of the inner layer coils 134 to reduce distortions in the baseline Bi 1 magnetic field. The currents processor 170 may select appropriate currents based on known configurations of the inner layer coils 134 and on the information of the magnetic field non-uniformity that needs to be corrected.
  • Non-uniformity of the baseline B 1 1 magnetic field may be determined in various ways, such as, for example, by acquiring a magnetic field map using a magnetic field mapping magnetic resonance sequence executed by the scanner 100, by reading optional magnetic field sensors (not shown) disposed in the bore 104, by performing a priori computation of the expected magnetic field distortion produced by introduction of the imaging subject 106, or so forth.
  • Magnetic field measurement sequences may be intermixed with the imaging sequence to check the baseline Bi magnetic field magnitude periodically, e.g. after each slice or batch of slices.
  • the currents processor 170 may control an inner layer coil controller 172 to energize one or more of the inner layer coils 134 at the selected currents. Dynamic, i.e., pulsed, control of the coil current settings is contemplated.
  • the inner layer coils 134 are switched between slices or batches of slices.
  • the inner coil array 130 may be driven by a constant current source.
  • the various kinds of dipole impedance modification methods which include, for example, using resistors, capacitors, inductors or combinations of resistors, capacitors, and inductors may be applied.
  • the coil arrays 130 of the inner coil layer 126 may be arranged in first and second levels 210, 212 in the axial direction z.
  • the coil arrays 130 of the inner coil layer 126 may be arranged into multiple levels.
  • the coil elements 134 of the coil arrays 130 of the inner coil layer 126 may have various arrangements.
  • the coil elements 134 of each level 210, 212 of the coil arrays 130 may be arranged in a ring in which the coil elements 134 overlap at the same level and between the first and second levels 210, 212.
  • Each level or ring 210, 212 of coil elements may be laid out according to design considerations. For example, if electrical dipoles are used for the coil array 130 of the inner coil layer 126, the coil elements 134 may be gapped or clustered. The clustered dipoles may form any pattern. An example of dipole clusters includes crosses formed by two dipoles that are orthogonal to one another. Other patterns are also contemplated. [00044] With continuing reference to FIGURE IA and further reference to FIGURE
  • each coil element 132, 134 includes electronic circuitry to provide an appropriate coupling between the outer and inner coil layers 124, 126.
  • the amount of coupling required for each inner layer coil element 134 may be determined by a coupling process 230 which may use a full- wave numerical approach.
  • the combination of frequency detuning and resistive attenuation may be used to scale the power down appropriately.
  • the numerical approach may apply, for example, the method of moments estimation, known in the art, with the presence of the imaging subject 106.
  • the method of moments estimation may start with the analysis of selected individual coil elements, for example, four individual non- overlapping elements.
  • all combinations of frequency detuning and resistive attenuation for the best local Bi magnetic field homogeneity performance may be searched. If, in block 244, it is determined that the best combination of the coupling elements is not found, the flow proceeds to the block 242. If, in block 244, it is determined that the best combination of the coupling elements is found, then the flow proceeds to the block 240 and additional coil elements may be added to the analysis.
  • the coupling of other four elements that overlap with the previous group of four elements is optimized based on a pre-selected criterion with the presence of their nearest neighbors, which now take the optimized frequency detuning and resistive attenuation.
  • an exhaustive search may be applied to find the best global homogeneity performance in a large range of axial slices.
  • the flow may exit 246 the process 230 from block 240 once the optimal coupling of all coil elements is determined.
  • the first round of optimization finishes once the initial coupling of all eight elements is determined. Another round of optimization is possible after the first round.
  • the results typically converge after at two rounds of optimizations.
  • Such strategy belongs to multi-directional optimization schemes. Any advanced method in that category, such as Powell's method, may also be used.
  • a B 1 magnetic field map 300 of the conventional 32-element shielded birdcage coil on an axial slice that needs to be homogenized is illustrated.
  • the profile 300 includes a local maxima 310 disposed about a center area 312 of the region of interest.
  • Local minima 320 are disposed about peripheral regions 322.
  • the inhomogeneous pattern in the peripheral regions 322 is not uniform in the azimuthal direction.
  • FIGURE 3B a corrected Bi magnetic field map 350 of the conventional 32-element shielded birdcage coil of FIGURE 3 A is illustrated.
  • the secondary Bi" magnetic field generated by the inner layer coil array 130 is superimposed on the profile 300.
  • a single inner layer coil element 134 is used to provide the secondary Bj" magnetic field excitation.
  • the local homogeneity of the Bi magnetic field is improved at the azimuthal location corresponding to the position of the coil element 134.
  • FIGURE 4 a substantially homogenized B 1 magnetic field map 400 of the conventional 32-element shielded birdcage coil of FIGURES 3 A and 3B is illustrated.
  • the secondary B 1 " magnetic field generated by the inner layer coils 134 is superimposed on the profile 300.
  • a single-level eight- element overlapped oval coil array 130 is used to provide the secondary B 1 " magnetic field excitation.
  • the capacitive coupling between the nearest neighbors for the overlapped loop coils 134 is substantially reduced or absent.
  • the cost weighted deviation represents a measure of Bi magnetic field inhomogeneity across several axial slices.
  • low cost implies higher degree of B 1 magnetic field homogeneity.
  • Low cost may be achieved either by resistive attenuation at a fixed resonant frequency, by frequency detuning with no resistive attenuation, or by a combination of resistive attenuation and frequency detuning.
  • the cost changes smoothly, not drastically, in the vicinity of the lowest cost point. Since the resonant frequency of loop coils changes only slightly with respect to small imaging subjects, the above observation indicates that if the inner layer coil array 130 is optimized with respect to one small imaging subject, its performance may still be acceptable to other small imaging subjects. Thus, exemplary embodiments described above may be simplified as the coil array 130 of the inner coil layer 126 does not need to be designed with respect to specific subjects.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

La présente invention concerne un appareil d'imagerie comprenant : un aimant principal destiné à générer un champ magnétique principal B0 sensiblement uniforme dans une zone d'examen ; et un système de bobine comprenant une première couche de bobine et une seconde couche de bobine disposée de façon sensiblement parallèle à la première couche de bobine avec un espace d'air défini dans une direction radiale, la première couche de bobine comprenant un premier ensemble de bobines, la seconde couche de bobine comprenant un second ensemble de bobines, les premier et second ensembles de bobines étant couplés et coopérant pour produire de façon sélective un champ magnétique B1 préspécifié dans la zone d'examen.
PCT/US2008/001911 2006-12-07 2008-02-13 Contrôle de profil de transmission en irm WO2008100546A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US12/449,514 US8125225B2 (en) 2006-12-07 2008-02-13 Transmit profile control in MRI

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US90097207P 2007-02-13 2007-02-13
US60/900,972 2007-02-13

Publications (1)

Publication Number Publication Date
WO2008100546A1 true WO2008100546A1 (fr) 2008-08-21

Family

ID=39690417

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2008/001911 WO2008100546A1 (fr) 2006-12-07 2008-02-13 Contrôle de profil de transmission en irm

Country Status (1)

Country Link
WO (1) WO2008100546A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102009024077A1 (de) * 2009-06-05 2010-12-09 Siemens Aktiengesellschaft Auswahlverfahren geeigneter Körpermodell-Positionen für eine SAR-Überwachung von MR-Systemen mit voneinander unabhängig betriebenen Vielkanal-Sende-Antennen (Transmit Array)
WO2013011406A3 (fr) * 2011-07-20 2013-03-14 Koninklijke Philips Electronics N.V. Bobines d'émission locales sans fil et ensemble à charge réglable
US9182468B2 (en) 2010-03-30 2015-11-10 Hitachi Medical Corporation RF reception coil and magnetic resonance imaging apparatus using same
WO2017198914A1 (fr) * 2016-03-29 2017-11-23 Université D'aix-Marseille Procede de controle de la repartition du champ magnetique radiofrequence dans un systeme d'imagerie par resonance magnetique
EP3511727A1 (fr) * 2018-01-11 2019-07-17 Koninklijke Philips N.V. Calage +b1 actif de bobines de transmission

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5296810A (en) * 1992-03-27 1994-03-22 Picker International, Inc. MRI self-shielded gradient coils
US5448214A (en) * 1994-06-15 1995-09-05 General Electric Company Open MRI magnet with superconductive shielding
US20050065431A1 (en) * 2003-09-23 2005-03-24 Arcady Reiderman Magnetic resonance imaging method and apparatus for body composition analysis
US6946840B1 (en) * 2001-03-08 2005-09-20 General Electric Company Integrated and independently controlled transmit only and receive only coil arrays for magnetic resonance systems
US7012430B2 (en) * 1997-11-26 2006-03-14 Medrad, Inc. Transmit/receive phased array coil system
US20060061360A1 (en) * 2002-06-14 2006-03-23 Leussler Christoph G Mr device provided with differently optimized rf coil arrays

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5296810A (en) * 1992-03-27 1994-03-22 Picker International, Inc. MRI self-shielded gradient coils
US5448214A (en) * 1994-06-15 1995-09-05 General Electric Company Open MRI magnet with superconductive shielding
US7012430B2 (en) * 1997-11-26 2006-03-14 Medrad, Inc. Transmit/receive phased array coil system
US6946840B1 (en) * 2001-03-08 2005-09-20 General Electric Company Integrated and independently controlled transmit only and receive only coil arrays for magnetic resonance systems
US20060061360A1 (en) * 2002-06-14 2006-03-23 Leussler Christoph G Mr device provided with differently optimized rf coil arrays
US20050065431A1 (en) * 2003-09-23 2005-03-24 Arcady Reiderman Magnetic resonance imaging method and apparatus for body composition analysis

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102009024077A1 (de) * 2009-06-05 2010-12-09 Siemens Aktiengesellschaft Auswahlverfahren geeigneter Körpermodell-Positionen für eine SAR-Überwachung von MR-Systemen mit voneinander unabhängig betriebenen Vielkanal-Sende-Antennen (Transmit Array)
DE102009024077B4 (de) * 2009-06-05 2012-09-13 Siemens Aktiengesellschaft Verfahren und Vorrichtung zur SAR-Überwachung bei Transmit-Array-Sendesystemen
US9182468B2 (en) 2010-03-30 2015-11-10 Hitachi Medical Corporation RF reception coil and magnetic resonance imaging apparatus using same
WO2013011406A3 (fr) * 2011-07-20 2013-03-14 Koninklijke Philips Electronics N.V. Bobines d'émission locales sans fil et ensemble à charge réglable
US9488705B2 (en) 2011-07-20 2016-11-08 Koninklijke Philips N.V. Wireless local transmit coils and array with controllable load
WO2017198914A1 (fr) * 2016-03-29 2017-11-23 Université D'aix-Marseille Procede de controle de la repartition du champ magnetique radiofrequence dans un systeme d'imagerie par resonance magnetique
US10816620B2 (en) 2016-03-29 2020-10-27 Universite D'aix-Marseille Method for controlling the distribution of the RF magnetic field in a magnetic resonance imaging system
EP3511727A1 (fr) * 2018-01-11 2019-07-17 Koninklijke Philips N.V. Calage +b1 actif de bobines de transmission
WO2019137984A1 (fr) * 2018-01-11 2019-07-18 Koninklijke Philips N.V. Homogénéisation b1 active de bobines de transmission
JP2021510569A (ja) * 2018-01-11 2021-04-30 コーニンクレッカ フィリップス エヌ ヴェＫｏｎｉｎｋｌｉｊｋｅ Ｐｈｉｌｉｐｓ Ｎ．Ｖ． 伝送コイルのアクティブｂ１＋シミング
US11194000B2 (en) 2018-01-11 2021-12-07 Koninklijke Philips N.V. Active b1+ shimming of transmission coils
JP7004828B2 (ja) 2018-01-11 2022-01-21 コーニンクレッカ フィリップス エヌ ヴェ 伝送コイルのアクティブｂ１＋シミング

Similar Documents

Publication Publication Date Title
US8125225B2 (en) Transmit profile control in MRI
US6396271B1 (en) Tunable birdcage transmitter coil
US8421462B2 (en) Sinusoidally resonant radio frequency volume coils for high field magnetic resonance applications
US7573270B2 (en) Radiofrequency magnetic field resonator and a method of designing the same
US8380266B2 (en) Coil element decoupling for MRI
EP2652516B1 (fr) Calage de champ b1 passif
US8013606B2 (en) Shielded multix coil array for parallel high field MRI
EP0918228A2 (fr) Bobine radiofréquences pour la résonance magnétique
CN104769451B (zh) 用于磁共振成像的z分段的射频天线
US6822450B2 (en) Multiple channel, cardiac array for sensitivity encoding in magnetic resonance imaging
US10261145B2 (en) System and method for improved radio-frequency detection or B0 field shimming in magnetic resonance imaging
US6650118B2 (en) RF coil system for an MR apparatus
KR20150021894A (ko) 상이한 타입의 보정 코일을 사용하여 mr 시스템을 환자 맞춤형으로 b0 균질화하기 위한 방법
EP2132583B1 (fr) Découplage de bobines
WO2008100546A1 (fr) Contrôle de profil de transmission en irm
US20080161675A1 (en) Ultra-Short Mri Body Coil
JPH0654822A (ja) 磁気共鳴イメージングのための非対称な無線周波コイル
Choi et al. A review of parallel transmit arrays for ultra-high field MR imaging
Lopez‐Rios et al. An 8‐channel Tx dipole and 20‐channel Rx loop coil array for MRI of the cervical spinal cord at 7 Tesla
Puchnin et al. Quadrature transceive wireless coil: Design concept and application for bilateral breast MRI at 1.5 T
Scholz et al. A 48-Channel Receive Array Coil for Mesoscopic Diffusion-Weighted MRI of Human ex vivo Brain Imaging on the 3T Connectome Scanner
Kim Homogeneous and heterogeneous resonators in ultrahigh-field MRI
GB2253909A (en) Coil arrangements in nuclear magnetic resonance apparatus

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 08725529

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 12449514

Country of ref document: US

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 08725529

Country of ref document: EP

Kind code of ref document: A1