Magnetic resonance imaging procedure

Abstract

The invention relates to a fixing device which comprises: - a main section which is intended to be held integral with the beam, the main section comprising a bottom surmounted laterally by two side walls (100b, 100c); - snap-fastening means configured to allow the crosspiece (30) to be snap-fastened between the side walls (100b, 100c) after engagement of said crosspiece (30) between the side walls (100b, 100c) by a front face, opposite the rear face, of the main section; - spring means configured to exert a force against the crosspiece (30), snap-fastened between the side walls (100b, 100c), in a direction going from the rear face towards the front face. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: magnetic resonance imaging method FIELD OF THE INVENTION

[0001] The present invention relates to the field of magnetic resonance imaging. In particular, the present invention relates to a magnetic resonance imaging method. More particularly, the magnetic resonance imaging method according to the present invention implements means for limiting the effect of ambient noise and in particular the electronic noise captured by electronic control modules of said device for forming an MRI image of a body by means of an MRI device. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Magnetic resonance imaging (MRI) is now widely used to non-invasively image the interior of bodies, particularly human bodies. In particular, magnetic resonance imaging makes it possible to probe the hydrogen nuclei, and particularly their nuclear spin, of water molecules that form part of the body under examination.

[0003] In this regard, an MRI device is provided with a magnet intended to impose a static magnetic field on the body (called the "main magnetic field"), under the effect of which, the nuclear spins associated with the hydrogen nuclei contained in the water molecules forming part of this body become polarized.

[0004] In particular, the magnetic moments associated with these spins are preferentially aligned along an axis, called the z axis, determined by the orientation of the main magnetic field so as to create a magnetization of the body.

[0005] An MRI device also includes gradient coils configured to produce small amplitude, spatially varying magnetic fields when a current is applied thereto. More particularly, the gradient coils are configured to produce a magnetic field component that is aligned parallel to the main magnetic field, and that varies linearly in amplitude with position along one of the x, y, or z axes (the x, y, and z axes being pairwise perpendicular).

[0006] Thus, the combined effects of the magnetic fields imposed by the gradient coils make it possible to spatially code each of the positions of the body intended to be probed.

[0007] An MRI device also comprises at least one radiofrequency (RF) coil intended to act as an RF transmitter / receiver. In particular, the at least one radiofrequency coil is configured to emit pulses of RF energy of a frequency equal to or close to the resonance frequency of the spins of the hydrogen nuclei and which is at least partly absorbed by these nuclei.

[0008] Once the RF emission is interrupted, the nuclear spins relax to return to their initial energy state and in turn emit an RF signal that can be collected by at least one RF coil. This RF signal is then processed using a computer and reconstruction algorithms to obtain an image of the body.

[0009] The main magnetic field, generally between 1.5 Tesla and 3 Tesla, makes it possible to achieve relatively reasonable signal-to-noise ratios and consequently to form images of the human body of sufficient quality over durations of the order of a minute or more.

[0010] However, there are circumstances in which it is not possible to implement a main magnetic field of such intensity. Portable MRI devices are an example. These generally comprise a permanent magnet or electromagnets of limited capacity, and cannot impose a main magnetic field of an intensity greater than 60 mT, or even greater than 200 mT, without penalizing the mass or size of the MRI device in question.

[0011] This limitation in terms of main magnetic field intensity directly affects the performance of the MRI device. In particular, the images obtained with such an MRI device are likely to have a quality that is significantly degraded by an unfavorable signal-to-noise ratio. This unfavorable signal-to-noise ratio is the consequence of the strong reduction in the magnetization present in the tissues due to the consideration of a low amplitude main magnetic field.

[0012] An aim of the present invention is to propose a magnetic resonance imaging method making it possible to reduce noise when the main magnetic field is weak and in particular less than 100 mT. BRIEF DESCRIPTION OF THE INVENTION

[0013] In order to achieve this aim, the invention proposes a method for imaging a part of a human or animal body by means of a magnetic resonance imaging device, said imaging method comprising the implementation of a belt surrounding a section of the trunk of said body called the contact section, said belt comprising a matrix of insulating material in which are arranged a set of wires ensuring electrical contact with the contact section, all of the wires being connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during an acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges.

[0014] According to one embodiment, the electrical potential is equal to the earth potential.

[0015] According to one embodiment, the imaging method uses an imaging device provided with a magnet defining a space inside which the part of the body is arranged during the acquisition of the magnetic resonance image, the magnet imposing during said acquisition a magnetic field of less than 100 mT, even more advantageously less than 50 mT.

[0016] According to one embodiment, the body part comprises the head.

[0017] According to one embodiment, the belt has a width of between 18 cm and 30 cm.

[0018] According to one embodiment, the matrix comprises a polyamide material.

[0019] According to one embodiment, the threads comprise at least one of the materials chosen from: silver, copper, tin.

[0020] According to one embodiment, the wires are arranged within the matrix so that said belt has a surface electrical resistance of less than 1 Ohm, advantageously less than 0.5 Ohm, even more advantageously less than 0.3 Ohm.

[0021] The invention also relates to a magnetic resonance imaging device provided with a belt comprising a matrix of insulating material in which are arranged a set of wires ensuring electrical contact with a contact section of the trunk of a body, all of the wires being connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges.

[0022] According to one embodiment, the belt has a width of between 18 cm and 30 cm.

[0023] According to one embodiment, the wires are arranged within the matrix so that said belt has a surface electrical resistance of less than 1 Ohm, advantageously less than 0.5 Ohm, even more advantageously less than 0.3 Ohm.

[0024] According to one embodiment, all of the wires are connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device. BRIEF DESCRIPTION OF THE FIGURES

[0025] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0026] [Fig.l] [Fig.l] is a schematic representation according to an exploded view of a magnetic resonance imaging device capable of being implemented within the framework of the present invention;

[0027] [Fig.2] [Fig.2] is a photograph of a section of a human torso and around which a belt is arranged in accordance with the principles set forth in the present invention;

[0028] [Fig.3] [Fig.3] is a schematic representation of a belt capable of to be implemented in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention relates to a method for imaging a part of a human or animal body. In particular, the imaging method uses a resonance imaging device, more particularly a so-called low-field resonance imaging device. By "low field" is meant a main magnetic field with an intensity of less than 200 mT, advantageously less than 100 mT, even more advantageously less than 50 mT.

[0030] Thus, [Fig.l] is a schematic representation of a magnetic resonance imaging device 1 capable of being implemented within the framework of the present invention.

[0031] The imaging device 1 comprises a magnet, and in particular a permanent magnet 2. The permanent magnet 2 may in particular extend along an elongation axis z.

[0032] More particularly, the permanent magnet 2 defines a housing 3 opening through a first opening 4 and a second opening 5 opposite one another along the elongation axis z.

[0033] In this respect, the permanent magnet 2 is arranged to allow the insertion of a body, and more particularly a human body, into the housing 3 through the first opening 4 along the elongation axis z.

[0034] The permanent magnet 2 is more particularly configured to impose a static magnetic field oriented along an axis perpendicular to the elongation axis z, in a zone, called the analysis zone, of the housing 3.

[0035] In this regard, the permanent magnet 2 may comprise an assembly of elementary magnets, and in particular arranged in series of Halbach rings. Document EP3368914B1 gives an example of this. Nevertheless, the invention is not limited to the sole configuration described in this document.

[0036] By way of example, the permanent magnet 2 is configured to impose a static magnetic field with an amplitude of less than 100 mT, advantageously less than 65 mT, and even more advantageously less than or equal to 50 mT.

[0037] The imaging system 1 also comprises a set of gradient coils 6. The gradient coils 6 are notably configured to produce small amplitude magnetic fields varying in space when a current is applied to them.

[0038] More particularly, the gradient coils 6 are designed to produce a magnetic field component that is aligned parallel to the static magnetic field, and that varies linearly in amplitude with position along one of the x, y or z axes (the x, y and z axes form an orthogonal coordinate system).

[0039] Thus, the combined effects of the magnetic fields imposed by the gradient coils 6 make it possible to spatially encode the signals originating from a body present in the housing 3 and intended to be probed. The spatial encoding is manifested in particular by a variation in the resonance energy of the nuclear spins of the hydrogen nuclei included in the body intended to be probed and present in the analysis zone. In other words, the nuclear spins of the hydrogen nuclei are subjected to a magnetic field which differs from one position to another.

[0040] The imaging system 1 further comprises a radiofrequency (RF) coil 7 intended to act as an RF transmitter / receiver. In particular, the at least one radiofrequency coil 7 is configured to emit RF energy pulses of a frequency equal to or close to the resonance frequency of the spins of the hydrogen nuclei and which is at least partly absorbed by these nuclei.

[0041] The radiofrequency coil 7 can be connected to pulse means 10 configured to impose the circulation of a current in said radiofrequency coil 7. More particularly, the pulse means 10 can be configured to allow the generation of current pulses in the radiofrequency coil 7. The pulse means are also advantageously implemented to power the gradient coils 6 in order to spatially code each of the positions of a body likely to be present in the housing 3.

[0042] The radiofrequency coil can also be connected to radiofrequency processing means 11 configured to process a radiofrequency signal capable of being received by the assembly formed by the radiofrequency coil 7.

[0043] The imaging system 1 may comprise a first interface 12 providing a link, on the one hand, between the pulse means 10 and the radiofrequency coil 7, and on the other hand, between the radiofrequency processing means 11 and the radiofrequency coil 7.

[0044] The imaging system 1 may, in addition, comprise a second interface 13 providing a link between the pulse means 10 and the gradient coils 6.

[0045] The pulse means 10, the radiofrequency processing means 11, the first interface 12 and the second interface 13 can be controlled by a control unit 14, for example a computer 14.

[0046] Thus, in operation, the radiofrequency coil 7 is arranged in the housing 3, and the body intended to be imaged in the interior volume of said radiofrequency coil 7.

[0047] The present invention therefore comprises a method for imaging a part of a human or animal body by means of a magnetic resonance imaging device, and in particular the imaging device 1 as described previously.

[0048] The imaging method notably comprises the implementation of a belt 50 (illustrated in [Fig.2] and in [Fig.3]) surrounding a section of the trunk of said body 60 called contact section 51.

[0049] The belt 50 comprises in particular a matrix of insulating material in which are arranged a set of wires ensuring electrical contact with the contact section, all of the wires being connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during an acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges. As shown in [Fig. 3], the belt 50 also comprises an electrical connection means 52 intended to allow the connection of said belt 50 to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during an acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges.

[0050] The belt can be between 18 cm and 30 cm wide.

[0051] The matrix may comprise a polyamide material.

[0052] Advantageously, the wires may comprise at least one of the materials chosen from: silver, copper, nickel, tin.

[0053] The wires may be arranged within the matrix so that said belt has a surface electrical resistance of less than 1 Ohm, advantageously less than 0.5 Ohm, even more advantageously less than 0.3 Ohm.

[0054] Table 1 below gives noise level measurements obtained for different configurations. In particular, this noise, given in microvolts, was measured during the implementation of an imaging method with a resonance imaging device having the following characteristics: • The belt 50 is arranged around the trunk of the body of an individual for imaging an arm of said individual (using a 27 cm scanner) or imaging the head of said individual (using the 32 cm scanner); • The main magnetic field is less than 50 mT; • Sequence used to measure noise: measurement without radio emission frequency with a receive bandwidth of 20 kHz (similar to the bandwidth used for a clinical sequence) • Acquisition of a single dimension; • Averaging of 4 acquisitions;

[0055] Measurement of the effective value in amplitude

[0056] In these tables, the “Phantom” line corresponds to the noise level obtained when measuring an image of a commercial phantom placed in the imaging device described above. This phantom has dielectric properties similar to human tissue. This measurement, used for reference purposes, does not implement the belt according to the terms of the present invention.

[0057] The lines “Volunteer 1” and “Volunteer 2” correspond to the noise level obtained during the measurement of a first individual (“First series”) and a second individual (“Second series”) placed in the imaging device described above. The measurements implement a belt 50 surrounding the trunk of the first and second individuals. The measurements implement a belt 22 cm wide. In both cases, the belt has a surface electrical resistance of less than 0.5 Ohm and is connected to the earth electrical potential during the measurement. The second column of the tables “Table 1” and “Table 2” presents the noise measured without a belt. The third column of the tables “Table 1” and “Table 2” presents the noise measured with a belt. Finally, the fourth and last column of the tables “Table 1” and “Table 2” presents the percentage reduction between the noise measured with and without a belt.The measurements are carried out according to the procedure described above.

[0058] Table 1: Use on 27 cm scanner, arm imaging Case Noise measured without belt (microvolt) Noise measured with belt (microvolt) Percentage reduction Phantom 0.06 NANA Volunteer 1 2.05 0.05 97.5% Volunteer 2 1.91 0.06 96.8%

[0059] Table 2: Use on 32 cm scanner, head imaging Case Noise measured without belt (microvolt) Noise measured with belt (microvolt) Percentage reduction Phantom 0.27 NANA Volunteer 1 15.64 0.29 98.1% Volunteer 2 13.54 0.22 98.4%

[0060] The “Voluntary 1” and “Voluntary 2” measurements have a noise level between 13 micro volts and 16 micro volts for use on a 32 cm scanner for head imaging, well above the reference measurements.

[0061] The implementation of the belt makes it possible to substantially attenuate electronic noise and produce good quality images.

[0062] The inventors were thus able to establish that the positioning of the belt 50 around the trunk of the body allows a relatively efficient flow of electrical charges and whatever the part of the body to be imaged. The resulting reduction in electronic noise allows for better resolution of the images obtained and thus the consideration of weaker magnetic fields, for example less than 100 mT, or even less than 50 mT.

[0063] The inventors were also able to observe that the positioning, for example of a bracelet made of the same material as the belt and positioned at the ankle or wrist, did not make it possible to obtain a reduction of electronic noise as effective and universal as the belt as implemented within the framework of the present invention.

[0064] Thus, the invention also relates to a magnetic resonance imaging device as described in relation to [Fig.l] and which comprises a belt 50 according to the present invention.

Claims

Claims

1. A method of imaging a part of a human or animal body by means of a magnetic resonance imaging device, said imaging method comprising the implementation of a belt surrounding a section of the trunk of said body called the contact section, said belt comprising a matrix of insulating material in which are arranged a set of wires ensuring electrical contact with the contact section, all of the wires being connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during an acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges.

2. Imaging method according to claim 1, wherein the imaging method implements an imaging device provided with a magnet defining a space inside which the body part is arranged during the acquisition of the magnetic resonance image, the magnet imposing during said acquisition a magnetic field of less than 100 mT, even more advantageously less than 50 mT.

3. The imaging method of claim 1 or 2, wherein the body part comprises the head.

4. Imaging method according to one of claims 1 to 3, wherein the belt has a width of between 18 cm and 30 cm.

5. An imaging method according to one of claims 1 to 4, wherein the matrix comprises a polyamide material.

6. Imaging method according to one of claims 1 to 5, in which the wires comprise at least one of the materials chosen from: silver, copper, tin.

7. Imaging method according to one of claims 1 to 6, in which the wires are arranged within the matrix so that said belt has a surface electrical resistance of less than 1 Ohm, advantageously less than 0.5 Ohm, even more advantageously less than 0.3 Ohm.

8. Magnetic resonance imaging device provided with a belt comprising a matrix of insulating material in which are arranged a set of wires ensuring electrical contact with a contact section of the trunk of a body, all of the wires being connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device during acquisition of a magnetic resonance image of a part of the human body so as to allow a flow of electrical charges.

9. An imaging device according to claim 8, wherein the belt is between 18 cm and 30 cm wide.

10. An imaging device according to claim 8 or 9, wherein the wires are arranged within the matrix such that said belt has a surface electrical resistance of less than 1 Ohm, advantageously less than 0.5 Ohm, even more advantageously less than 0.3 Ohm.

11. Imaging device according to one of claims 8 to 10, in the set of wires are connected to the same electrical potential as all of the electrical and electronic elements constituting the magnetic resonance imaging device.

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