WO2020178766A1 - Appareil irm et méthode permettant un changement du champ magnétique statique b0 depuis une première valeur vers une seconde valeur - Google Patents

Appareil irm et méthode permettant un changement du champ magnétique statique b0 depuis une première valeur vers une seconde valeur Download PDF

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Publication number
WO2020178766A1
WO2020178766A1 PCT/IB2020/051877 IB2020051877W WO2020178766A1 WO 2020178766 A1 WO2020178766 A1 WO 2020178766A1 IB 2020051877 W IB2020051877 W IB 2020051877W WO 2020178766 A1 WO2020178766 A1 WO 2020178766A1
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WO
WIPO (PCT)
Prior art keywords
magnetic field
unit
static magnetic
generate
magnet
Prior art date
Application number
PCT/IB2020/051877
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English (en)
Inventor
Zelio CERASANI
Igor RIGON
Original Assignee
BRAGA, Massimo
PENZO, Matteo
JACARONI, Giulio
Fenice Med S.R.L.
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.)
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Application filed by BRAGA, Massimo, PENZO, Matteo, JACARONI, Giulio, Fenice Med S.R.L. filed Critical BRAGA, Massimo
Publication of WO2020178766A1 publication Critical patent/WO2020178766A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/445—MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging
    • 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
    • G01R33/3628—Tuning/matching of the transmit/receive coil
    • G01R33/3635—Multi-frequency operation

Definitions

  • the present invention relates to an apparatus for data acquisition and the creation of magnetic resonance images, and to a method for data acquisition and creation of magnetic resonance images.
  • Magnetic resonance imaging Magnetic resonance imaging
  • Bo static magnetic field
  • radiofrequency electromagnetic fields
  • the object under examination usually a patient, is immersed in the main static magnetic field and uniform Bo so that the magnetization vectors of the protons of the atoms begin a precession motion about an axis that has the same direction as the field Bo.
  • the precession frequency is said the Larmor frequency and is dependent on the physical properties of the nuclei under examination, and in particular on the gyromagnetic ratio y and on the intensity of the field Bo according to the relation:
  • the radiofrequency pulse After having excited the system to a sufficient degree, the radiofrequency pulse is interrupted. Under the action of Bo, the system will tend to return to a state of equilibrium, thereby transferring the accumulated energy to the external environment in the form of an electromagnetic wave.
  • the relaxation signal is collected by RF antenna elements called RF coils (MRI - Magnetic Resonance Imaging - coils ) .
  • the signal detected during the relaxation process is processed and, on account of this, it is possible to obtain data and to create the images by means of the principle of physics of nuclear magnetic resonance.
  • the main magnetic field Bo In order to award the various signals received a spatial position and therefore to reconstruct the images, the main magnetic field Bo needs to be changed in the three directions by means of three field gradients: Gx, Gy and Gz .
  • the apparatus comprises a main magnet that generates the static magnetic field Bo, which, in clinical applications, assumes values that are generally between 0.2 T and 4 T.
  • a shield is generally positioned between the field coils and the gradient coils.
  • the radiofrequency coils with which a magnetic resonance system is provided can essentially be categorized into two categories: body coil and other RF coils intended for specific anatomical districts.
  • the body coil is generally housed inside the space that also contains the magnet and the gradient coils.
  • This type of coil is generally both a transmitting and a receiving (T/R) coil and can solely be used to transmit the radiofrequency impulse or to transmit the impulse and then to receive the return signal that originates from the anatomical district under examination. [0017] In particular, it is used exclusively as a transmitter (T) when used in combination with a coil that is exclusively assigned with collecting the magnetic resonance signal.
  • said coil can be used as a T/R coil, for example, when examining particularly voluminous districts, such as the chest or abdomen.
  • the dedicated RF coils are the specific types of antenna that are directly applied to the patient and are conceived and designed for optimizing the transfer and collection of the signal from the particular anatomical district, these can be exclusively receiving (R) or both transmitting and receiving (T/R) .
  • the patient is typically laid down on a bed that, by means of an electromechanical movement system, allows to correctly position the anatomical district to be examined inside the magnet.
  • the electronic unit necessary for managing the different peripheral devices that the system consists of.
  • the electronic part may be of different types and it may comprise different components; in any event, the electronics can be summarized, purely by way of example, as indicated in the following.
  • the electromagnetic fields of the RF coils are managed by means of an RF amplifier that can generate radiofrequency signals in a frequency band that is dependent on the static field Bo of the system.
  • the three gradients are typically managed individually by devices called gradient amplifiers that, in turn, are generally supplied with power by one or more dedicated power supplies .
  • the signals collected in order to form the image are sent to a reconstructor that reconstructs the images.
  • the reconstructor is a computer provided with dedicated software and algorithms.
  • the magnetic resonance images are currently generally processed by the signals from the hydrogen nuclei 1 H, even if it is known that the physical phenomenon of the nuclear magnetic resonance would also make it possible to receive information from other species, such as 2 H, 15 N, 17 0, 3 He, 13 C, 19 F, 23 Na, 31 P and 129 Xe .
  • broadband coils may be provided, adapted to receive different frequencies but this would worsen the performances of the entire system in terms of the quality of the images. Furthermore, the costs associated with the apparatus would be considerably greater and the system would also be more complex than the current systems.
  • the present invention intends to overcome the limitations of the current nuclear magnetic resonance systems, making the collection of information from not only the hydrogen atoms 1 H, but also from other nuclei, for example 2 H, 15 N, 17 0, 3 He, 13 C, 19 F, 23 Na, 31 P and 129 Xe, in order to be able to obtain images, and therefore magnetic resonance examinations possible, which are able to provide more information than the systems of the prior art.
  • Fig. 1 is a schematic view of a possible embodiment of an apparatus according to the present invention.
  • Fig. 2 is a schematic view of an alternative embodiment of an apparatus as per the present invention.
  • the apparatus 12 comprises : - a first unit 14 adapted to generate a static magnetic field Bo, comprising a main magnet 140;
  • a second unit 16 adapted to generate three magnetic field gradients in three directions (x, y, z) that are perpendicular to one another, comprising gradient coils 160;
  • a third unit 18 adapted to generate and receive an electromagnetic field having a frequency that is equal to the Larmor frequency, comprising at least one radiofrequency coil 180;
  • control unit 20 that is connected to the second unit 16 and to the third unit 18.
  • the apparatus is characterized in that it comprises an auxiliary unit 22 comprising at least one auxiliary magnet 220, which is adapted to selectively generate a second static magnetic field Boi so as to change the value of the magnetic field Bo generated by the first unit 14 to a value Bo' .
  • the second unit 16 adapted to generate the magnetic field gradients may comprise a unit for managing the gradients 50, comprising gradient amplifiers for each gradient coil, which are supplied with power by at least one power supply.
  • the auxiliary unit 22, which is adapted to selectively generate a second static magnetic field Boi, may comprise an auxiliary power supply unit 40.
  • the main magnet 140 can be an electromagnet, a permanent magnet or a superconductor magnet.
  • the main magnet can be adapted to generate a static magnetic field Bo that, for clinical applications, is generally between 0.2 T and 4 T. However, larger ranges, for example up to 8 T or even higher, are possible .
  • the first unit 14 can be connected to the control unit 20, for example when the main magnet is an electromagnet or superconductor magnet.
  • the first unit can be provided with an independent control unit (not shown in the attached figures) .
  • a shield 24 can be positioned between the main magnet 140 and the gradient coils. As shown schematically in Fig. 1, the shield can be grounded.
  • the radiofrequency coils 180 with which a magnetic resonance system is provided can be of two types: a body coil 182 and RF coils 184 intended for specific anatomical districts.
  • the third unit 18 can be provided with at least one power supply unit 60 for the radiofrequency coils 180, which is adapted to send signals to the body coil 182 and to the dedicated RF coils 184.
  • the apparatus 12 can comprise an electronic unit 70 that is adapted to receive the signals from the at least one radiofrequency coil 180, and may be suitable for pre-processing the signals.
  • the apparatus may also comprise a reconstructor 80, which is connected to the electronic unit 70 that receives the signals processed by the electronic unit 70 in order to present the data received, and to possibly reconstruct the magnetic resonance image.
  • a reconstructor 80 which is connected to the electronic unit 70 that receives the signals processed by the electronic unit 70 in order to present the data received, and to possibly reconstruct the magnetic resonance image.
  • the electronic unit 70 and the reconstructor 80 will not be further analyzed because they are elements known per se to an expert in the field.
  • the apparatus 12 can comprise a bed on which the subject to be subjected to resonance is positioned and a bed-controlling unit 30.
  • the bed-controlling unit 30 can be connected to the control unit 20.
  • the control unit 20 is adapted to generate the system signals directed at the radiofrequency amplifiers, to the gradients and to the signal receivers. In addition to this, it is adapted to generate a reference signal that is sent to each peripheral device in order to synchronize the different activities. Therefore, with the type of scanning and the time base specified, the control unit 20 is adapted to manage the signals sent by coordinating the times at which the signal is received by the receiving coils. These signals, entering the receivers, are therefore synchronized by the control unit 20 and converted into images and/or graphs that shall therefore be sent directly to and displayed directly on the operating station 26 of the operator.
  • the body coil 182 can be housed inside the space that also contains the main magnet 140 and the gradient coils 160.
  • the body coil 182 can be both a transmitter and a receiver (T/R) . Therefore, the body coil 182 can be exclusively used for transmitting the radiofrequency pulse or for transmitting the pulse and then receiving the return signal from the anatomical district under examination.
  • the body coil 182 When the body coil 182 is only a transmitter or is only used for transmission, it can be used in combination with a dedicated RF coil 184 exclusively assigned with collecting the magnetic resonance signal.
  • said coil can also be used as a T/R coil, typically when examining particularly voluminous districts, such as the chest or abdomen.
  • the dedicated RF coils 184 are particular probe types that are directly applied to the patient and are conceived and designed to optimize the transfer and collection of the signal from the particular anatomical district.
  • the dedicated RF coils 184 can be exclusively receiving coils (R) or both transmitting and receiving coils (T/R) .
  • the radiofrequency coils 180 can comprise a transmission band and a receiving band of a few MHz (the band is less selective and the coil is more selective) and centered at the Larmor frequency, which is dependent on the static magnetic field of the system. For example, for systems from 1.5 T, for hydrogen 1 H this is equal to approximately 63.87 MHz.
  • a shield 24 can be provided between the gradient coils 160 and the body coil 182.
  • the at least one auxiliary magnet 220 is provided between the main magnet 140 and the gradient coils 160.
  • the at least one auxiliary magnet 220 can be positioned on the outside of the body coil.
  • the at least one auxiliary magnet 220 can be an electromagnet or a superconductor magnet.
  • the at least one auxiliary magnet 220 When the at least one auxiliary magnet 220 is supplied with power, it will generate a magnetic field Boi that will be added to or subtracted from the main magnetic field Bo generated by the main magnet 140. When the winding of the auxiliary magnet 220 is not supplied with power, the static magnetic field will be equal to that generated by the main magnet 140.
  • the power supply of the auxiliary magnet may be adapted to be adjusted such that, with regards to the field Bo and on the basis of the atom intended to be examined and on the scanning type that has been selected by the operator, the power supply is adapted to generate a predetermined electric current value having a specific direction, for a certain time interval.
  • auxiliary winding is inserted into a superconductor system and is positioned between the main magnet 140 and the gradient coils 160.
  • the invention is also applicable to systems comprising different types of magnets and different configurations.
  • several auxiliary magnets 220 might be required, for example two.
  • additional shielding, a system for compensating for induced currents, etc. can be provided according to specific requirements, for example in order to prevent spurious currents being created in the various windings, which are able to deform the various fields and change the values for the various physical quantities that are outside the range of optimum values.
  • the apparatus may comprise a magnetic field measurer (not shown) for measuring and verifying the effective attainment of the desired magnetic field.
  • the at least one auxiliary magnet 220 adapted to selectively generate a second static magnetic field Boi can be connected to power supply means that can be selectively activated.
  • the apparatus 12 is therefore adapted to acquire data and generating magnetic resonance images - nuclear magnetic resonance imaging (MRI) - by using the signal coming from a plurality of atomic species, varying the static magnetic field and always using the same radiofrequency coils 180 used for the transmission and receipt of the RF signals.
  • MRI nuclear magnetic resonance imaging
  • the static magnetic field can be changed using the at least one auxiliary magnet 220, which can generate at least one magnetic field Boi that can be concordant or discordant with respect to the magnetic field Bo generated by the main magnet 140.
  • the intensity of the magnetic field Boi is dependent on the current intensity that is passed through said windings, while the direction is dependent on the direction of the currents that are passed through the auxiliary windings.
  • the resultant static magnetic fields Bo' can also be preset in terms of the type of nucleus from which information is intended to be obtained and can be selectable by the operator by means of an operating station
  • a similar table can be created by keeping the resonance frequencies of the various nuclei almost constant, for example around 63,87 MHz (with a deviation of ⁇ 0,5 MHz assuming a transmission band and a receiving band for the various RF coils that is equal to 1 MHz and centered at 63.87 MHz), and by changing the static magnetic field in which the various nuclei are immersed.
  • the method for data acquisition and the creation of magnetic resonance images according to the present invention comprises the steps of:
  • a first unit 14 adapted to generate a static magnetic field Bo, comprising a main magnet 140;
  • a second unit 16 adapted to generate three magnetic field gradients in three directions (x, y, z) that are perpendicular to one another, comprising gradient coils 160;
  • a third unit 18 adapted to generate and receive an electromagnetic field having a frequency that is equal to the Larmor frequency, comprising at least one radiofrequency coil 180;
  • control unit 20 connected to the second unit 16 and to the third unit 18;
  • step (a) In accordance with a possible embodiment, step (b) is
  • the method provides a first step in which the data coming from a first atomic species that is intended to be analyzed is acquired.
  • This step can be carried out in the presence of the sole static magnetic field Bo generated by the main magnet 140, or with a magnetic field obtained as the sum of the magnetic field Bo and the magnetic field Boi generated by the at least one auxiliary magnet 220.
  • a second step takes place in which the data of a second atomic species is acquired.
  • This step obviously depends on the preceding step in regards to the definition of the magnetic field, and can be carried out in particular with a magnetic field that is obtained as the sum of the magnetic field Bo and the magnetic field Boi generated by the at least one auxiliary magnet 220 or in the presence of the sole static magnetic field Bo generated by the main magnet 140.
  • the second value of the magnetic field can be predetermined so as to make the nuclei of the second atomic species to be examined resonate at the same Larmor frequency as the first species.
  • the data of the first species and that of the second species can therefore advantageously be acquired by using the same radiofrequency coils for both transmission and receipt.
  • the data from the first atomic species and from the second atomic species are therefore processed and the relative images or graphs are created.
  • the method according to the present invention could comprise a second change to the resultant static magnetic field in order to enable a third acquisition and to collect the data relating to a third atomic species.
  • the method could therefore be repeated in order to also acquire data from other atomic species of interest .
  • the data can also be processed and images or graphs generated at different times to those mentioned above .
  • the apparatus of the present invention can be used to stabilize the presence and/or the concentration of one or more atomic species of interest .
  • the apparatus remains substantially the same with respect to that described above, but the information that is received by the control unit is not converted into an image, but is made available in terms of data relating to the presence and/or to the concentration .
  • the apparatus can also be used in a diagnostic scanning method for detecting the presence and/or the concentration of specific atomic species of interest .
  • the step of processing and displaying the images could follow each acquisition step.
  • This second way of carrying out the examination may be preferable when wanting to obtain as soon as possible information regarding the first atomic species analyzed. For example, it would already be possible to immediately start examining the information from the first acquisition while the examination is still taking place. [0096]
  • the examples given are not intended to be restrictive in any way with regard to the mode of acquiring, processing and presenting the data.
  • the resonance frequency of hydrogen 3 ⁇ 4 is 63.87 MHz.
  • fluorine 19 F which has a gyromagnetic ratio g equal to 40.06 MHz/T.
  • g gyromagnetic ratio
  • the field will have to increase up to approximately 1.596 T and therefore the at least one auxiliary magnet 220 will have to generate a magnetic field of approximately 0.096 T that is concordant with the static magnetic field generated by the main magnet 140.
  • Another application relates to the fluorine atom that could be used as a contrast liquid for identification, localization and treatment of tumors, similarly to what is already the case with PET (Positron Emission Tomography) , but with a contrast liquid that does not have to be made radioactive.
  • a contrast liquid is generally used, in which the fluorine atoms are radioactive ( 18 F) and bonded to a transporter molecule that allows them to accumulate at the points of interest (generally cancerous cells) .
  • the fluorine atoms which are radioactive during the decay, emit positrons and, on account of suitable systems, it is possible to localize the position of the tumors and to study the activity thereof.
  • images are not formed by a fixed static magnetic field and by using different RF coils for the different resonance frequencies or broadband frequencies, together with all the problems that ensue, but by varying the static magnetic field with the aid of one or more additional auxiliary windings.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

L'invention concerne un appareil (12) permettant l'acquisition de données et la création d'images de résonance magnétique, comprenant : une première unité (14) permettant de générer un champ magnétique statique B0, comprenant un aimant principal (140) ; une deuxième unité (16) permettant de générer trois gradients de champ magnétique dans trois directions (x, y, z) perpendiculaires les unes aux autres, comprenant des bobines de gradient (160) ; une troisième unité (18) permettant de générer et de recevoir un champ électromagnétique rotatif possédant la fréquence de Larmor, comprenant au moins une bobine radiofréquence (180) ; et une unité de commande (20) connectée à la deuxième unité (16) et à la troisième unité (18). L'appareil (12) comprend une unité auxiliaire (22) comprenant au moins un aimant auxiliaire (220), permettant de générer sélectivement un second champ magnétique statique B01 de façon à modifier la valeur du champ magnétique B0 générée par la première unité (14) vers une valeur B0.
PCT/IB2020/051877 2019-03-04 2020-03-04 Appareil irm et méthode permettant un changement du champ magnétique statique b0 depuis une première valeur vers une seconde valeur WO2020178766A1 (fr)

Applications Claiming Priority (2)

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IT102019000003097 2019-03-04
IT102019000003097A IT201900003097A1 (it) 2019-03-04 2019-03-04 Apparato e procedimento per l’acquisizione di dati e la creazione di immagini mediante risonanza magnetica

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5281913A (en) * 1990-06-29 1994-01-25 The Regents Of The University Of California NMR relaxometry using fixed RF frequency band
WO2017203330A1 (fr) * 2016-05-27 2017-11-30 Synaptive Medical (Barbados) Inc. Imagerie par résonance magnétique différentes espèces de spin nucléaire avec la même bobine radiofréquence

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5281913A (en) * 1990-06-29 1994-01-25 The Regents Of The University Of California NMR relaxometry using fixed RF frequency band
US5629624A (en) * 1990-06-29 1997-05-13 The Regents Of The University Of California Switched field magnetic resonance imaging
WO2017203330A1 (fr) * 2016-05-27 2017-11-30 Synaptive Medical (Barbados) Inc. Imagerie par résonance magnétique différentes espèces de spin nucléaire avec la même bobine radiofréquence

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