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
  • G01R33/56—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
• • 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
  • G01R33/288—Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room

Definitions

• the present invention relates to a magnetic field corrector device intended to be used for magnetic resonance imaging (MRI).
• MRI magnetic resonance imaging
• SNR signal-to-noise ratio
• Clinical MRI devices in particular with a magnetic field equal to 1.5T or 3T, are equipped with a volume antenna, called "body antenna", used to transmit the RF magnetic field, i.e. radiofrequency, or B 1+ field, of excitation to the nuclei that we wish to study.
• the purpose of this antenna is to produce a perfectly homogeneous signal in order to ensure the quality of the MRI images used by radiologists.
• US Patent 7,639,011 discloses an RF magnetic field delivery correction device configured to position over a patient under MRI examination. This device comprises conductive dipole strips arranged in parallel on a support.
• Application US 2015/196225 describes an antenna element for an MRI diagnostic tool to be placed under the breast and which may comprise a combination of conductive tracks and capacitors selected for an amplification of the RF magnetic field.
• Application GB 2,580,011 discloses a device for concentrating a magnetic field of radiofrequency signals in an MRI system.
• the device comprises a plurality of conductive elements arranged in a matrix.
• the device may include semiconductors each connected between a pair of two conductive elements. These semiconductors require an external power supply.
• Patent CN 102723608 discloses a metamaterial comprising microstructures arranged on a substrate. These microstructures comprise conductive wires forming open rings and inductance patches connected in series with the conductive wires.
• Application US 2010/213941 discloses an antenna for exciting or detecting magnetic resonance in an object to be examined.
• the antenna comprises at least one line resonator and a conductive loop interrupted by at least one capacitor. This document concerns an active system to be connected to a magnetic wave generation device.
• the subject of the invention is a magnetic field correction device in magnetic resonance imaging, intended to be positioned on a zone of the body of a patient during an examination in magnetic resonance imaging, comprising a substrate and at least one track disposed on said substrate, said at least one conductive track comprising at least two segments interconnected by at least one reactive electrical component.
• the invention makes it possible to solve the problems of homogenization of the radiofrequency magnetic field with a planar, fine and flexible structure which is perfectly compatible with the conditions of clinical examination in MRI.
• the reactive electrical components make it possible to correct the resonance frequency of the metal track or tracks and to reduce the quality factors of the resonances, and thus to modify the RF magnetic field produced during the MRI examination.
• reactive electric component it should be understood that said component reacts to the passage of an electric current without power consumption or external power supply.
• the device is not powered by a radiofrequency wave generation device, thus constituting a passive system.
• the device during its operation, is traversed by a current created solely by an electromagnetic induction phenomenon.
• the invention also makes it possible to increase the signal-to-noise ratio of the MRI measurement in at least part of the human body without impacting the rest, while maintaining the Specific Absorption Rate (SAR) below the authorized limit.
• SAR Specific Absorption Rate
• the device according to the invention When it is worn by a patient during an MRI measurement using a transmission antenna and one or more reception networks, the device according to the invention makes it possible to obtain an image with better contrast in the usually empty areas. of signal for MRIs with intense magnetic fields. These low-signal areas are found in particular in the case of pelvic, abdominal or cardiac MRI examinations, with a 3T magnetic field.
• the reactive electrical components are preferably capacitors.
• the reactive electrical components are inductors.
• the reactive electrical components are preferably capacitors. Otherwise, the reactive electrical components are preferably inductors.
• the capacitance value of said capacitor is preferably between lpF and InF.
• its value is preferably between InH and
• the choice of the capacitance of the capacitor(s) or of the inductor(s) is linked to the length of the segments placed end to end and to the number of segments.
• Said at least one reactive electrical component may have an electronically adjustable capacitance or inductance value, for example using a suitable electronic circuit.
• Said at least one reactive electrical component may be a component mounted on the surface and soldered to the conductive track at the adjacent ends of two segments of said track.
• Said at least one conductive track comprises between one and fifteen segments. Increasing the number of segments makes it possible to control the distribution of the amplitude of the current flowing on the conductive track. This aspect makes it possible to adapt the size of the device according to the invention with respect to the targeted area.
• the segments are straight and aligned with each other.
• the device may comprise several conductive tracks, in particular of elongated shape and arranged on the substrate parallel to each other. These tracks are preferably not interconnected.
• All the conductive tracks can have the same length.
• All the conductive tracks can comprise the same number of segments, in particular two segments.
• the corresponding segments of the different conductive tracks preferably have the same length, the segments within the same conductive track being in particular of identical length.
• corresponding segments it is necessary to understand the same N th segment of the different metal tracks, N being an integer greater than 1 and less than the total number of segments of a metal track, counted according to the longitudinal tax according to which each track extends metallic.
• Said at least one conductive track is preferably made of a metal, preferably non-magnetic, in particular copper, silver or brass.
• said at least one conductive track is made of copper.
• the device may comprise between one and thirty conductive tracks, in particular
• the width of said at least one track is preferably between 1 mm and 25 mm, being in particular equal to 12.5 mm.
• the spacing between each conductive track, measured edge to edge, is preferably between 1 mm and 100 mm, being in particular equal to 50 mm.
• the thickness of said at least one track is preferably between 0.005 mm and 0.2 mm.
• the length of said at least one track is preferably between 0.1 m and 1 m, better still between 60 cm and 85 cm, being in particular equal to 70 cm.
• the thickness of said substrate is preferably between 0.01 mm and 1.6 mm, being in particular equal to 0.4 mm.
• the substrate is flexible. This ensures the flexibility of the entire device.
• the substrate can be made of a thermoplastic polymer, comprising in particular at least one epoxy resin composite or a polyimide, being in particular made of Kapton ® .
• the substrate is made of a low-loss material whose loss angle d is such that tan( ⁇ ) ⁇ 0.025.
• Another subject of the invention is an assembly comprising a device according to the invention, and a protective cover, made in particular of a thermoplastic material, in particular a thermoplastic polymer, intended to receive the device.
• the cover may include a polymer-impregnated fabric compatible with safety and hygiene rules for healthcare and hospital applications.
• the invention also relates to a method for manufacturing a magnetic field corrector device according to the invention and intended to be positioned on a zone of the body of a patient during an examination by magnetic resonance imaging, method in which at least one conductive track is printed on a substrate, said at least one conductive track being cut into at least two segments interconnected by at least one reactive electrical component.
• the number of track(s), the number of segments, the width, the length and/or the thickness of said at least one track, the spacing between each conductive track, and/or the component(s) electrical reactive(s), in particular the capacitance value in the case of capacitor(s) can be chosen according to the field of view of the area of the patient's body to be examined and/or the value of the magnetic field static implemented during said magnetic resonance imaging examination.
• the specific resonance frequency of the conductive track or tracks which is advantageously set so as to be slightly higher, by a few percent, than the Larmor frequency used by MRI devices, in particular an MRI scanner in the case of MRI imaging.
• Numerical simulation tools for example that of electromagnetic field simulation by the finite element method, make it possible to optimize the aforementioned characteristics of the device according to the targeted areas of the body. Typical models of radio frequency antennas and human bodies are used in these simulations. The use of the digital tool makes it possible to best describe the propagation of electromagnetic waves in the human body, which is a complex and heterogeneous environment.
• Another subject of the invention is a method for using a magnetic field corrector device according to the invention, comprising the placement of at least one corrector device on and/or under the zone of the patient's body to be examined. by magnetic resonance imaging.
• Said zone can be the pelvic, abdominal or cardiac, cerebral, cervical zone, or the joints, in particular the knee, the ankle, the elbow, the shoulder and the wrist.
• a first correction device can be placed on the area of the patient's body to be examined and a second correction device can be placed under the area of the patient's body to be examined.
• the reactive electrical component(s) of the first device may be different from the reactive electrical component(s) of the second device.
• the intensity of the static magnetic field implemented during said magnetic resonance imaging examination can be equal to 1.5T, 3T and 7T.
• Figure 1 shows an example of a device according to the invention
• Figure 2A represents the distribution of the Bi+ field obtained in a phantom M of a human simulation model by a body antenna without using the device according to the invention
• Figure 2B represents the distribution of the Bi+ field of figure 2A in the case where the device represented in figure 1 was used,
• Figure 3 illustrates an example of use of the device according to the invention
• Figure 4A represents a sagittal section of signal to noise ratio without using the device according to the invention
• Figure 4B shows the sagittal section of signal to noise ratio of Figure 4A in the case where the device shown in Figure 1 was used, and
• Figure 5 shows profiles of the signal to noise ratio taken on a horizontal line in the center of the images of Figures 4A and 4B.
• Illustrated in Figure 1 is an example of device 1 according to the invention used for MRI examinations for the pelvic and abdominal areas, with a magnetic field equal to 3T.
• the device 1 comprises in the illustrated example fifteen metal tracks 11, made of copper, of width w equal to 1.25 cm, spaced apart, edge to edge, by 1.25 cm, and of thickness equal to 0.01 cm. .
• the tracks 11 have a length L equal to 70 cm. These tracks 11 are cut into two segments S1, S2, interconnected by fifteen reactive electrical components 12, capacitors of capacitance lOpF in the example described.
• the tracks 11 are deposited on an FR-4 resin substrate (Flame Resistant 4) with a thickness equal to 0.04 cm.
• the device can be protected by a cover of suitable size, for example sewn and made of a thermoplastic polymer, in particular of Dartex.
• FIG. 2A represents the distribution of the Bi+ field obtained by using a body antenna in a phantom M of a human simulation model at 128 MHz, corresponding to the Larmor frequency of the proton for a magnetic field equal to 3T.
• the body antenna alone provides an inhomogeneous RF magnetic field, as seen by the dark areas showing low intensity.
• the homogeneity of the Bi+ radiofrequency magnetic field makes it possible, on the one hand, to guarantee a homogeneous tilt angle throughout the observation area, which guarantees the homogeneity of the contrast in the final MRI images.
• the tilt angle is a parameter used during all MRI acquisition sequences. It characterizes the angle formed by the average magnetization of the probed nuclei and the axis of the static magnetic field Bo. The value of the tilt angle is fixed by the amplitude and the duration of the radio frequency pulses generated by the transmitting antenna.
• the general increase in the intensity of the Bi+ radiofrequency magnetic field makes it possible to control the tilt angle with better efficiency, i.e. less power supplied by the generator.
• This aspect is essential, for the patient, with regard to electromagnetic safety, in terms of specific absorption rate, as presented in the table below.
• the two SAR factors either global, i.e. averaged over the whole of the phantom M, or local, i.e. say averaged over 10g of tissue, are reduced by the addition of one or two corrective devices according to the invention.
• the study of the signal-to-noise ratio is important for the quality of the final MRI images, a signal-to-noise ratio that is too low leading to difficulty or impossibility of diagnosis by a doctor.
• a significant increase in the signal-to-noise ratio also makes it possible to speed up the measurement if high threshold levels are reached.
• the measurements are carried out on an MRI scanner with a magnetic field equal to 3T with a phantom comprising a 20L container with a size of 40 ⁇ 40 ⁇ 20 cm 3 filled with water, representing an analogue of a human abdomen.
• Signal transmission is performed by the body antenna of the MRI scanner and signal reception by two multi-channel antenna arrays, a dorsal array and a ventral array.
• Two measurements are compared respectively carried out in a configuration not using a device according to the invention, corresponding to a reference measurement, and a so-called “double” configuration with two corrector devices inserted between the reception networks (not illustrated) and the surface of the phantom, as shown in figure 3, in which the dotted volume shows the measurement zone which contains the jerrycan, and the plates shaded show the positioning of the two devices according to the invention, in contact with the measurement volume.
• FIGS. 4A and 4B represent the sagittal sections of the signal to noise ratios obtained.
• FIG. 5 represents a profile of the signal-to-noise ratio taken on a horizontal line in the center of the images of FIGS. 4A and 4B.
• a marked improvement in the signal-to-noise ratio can be seen throughout the profile and more generally throughout the cut after insertion of the corrective devices according to the invention.
• the invention is not limited to the examples described above.

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• 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)

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• 2021
  • 2021-02-23 FR FR2101730A patent/FR3120129B1/fr active Active
• 2022
  • 2022-02-11 JP JP2023574754A patent/JP2024507010A/ja active Pending
  • 2022-02-11 EP EP22708082.7A patent/EP4298449A1/de active Pending
  • 2022-02-11 CN CN202280016500.7A patent/CN117043620A/zh active Pending
  • 2022-02-11 US US18/278,084 patent/US20240053424A1/en active Pending
  • 2022-02-11 WO PCT/EP2022/053380 patent/WO2022179863A1/fr active Application Filing

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