SQUID-based radio frequency detection and acquisition system and equipment comprising the same

Abstract

The present application relates to a SQUID-based radiofrequency detection and acquisition system and to an apparatus comprising the same. The radiofrequency detection and acquisition system, based on SQUIDs and arranged to be integrated into a nuclear magnetic resonance apparatus, comprises: a main detection antenna; a flux transformer, the flux transformer having an input winding connected to the main detection antenna; a low critical temperature SQUID device, the low critical temperature SQUID device capturing the magnetic flux generated by the output winding of the flux transformer and supplying a secondary detection signal; a cryogenic device, the cryogenic device cooling the SQUID device and the flux transformer; and a step of processing the secondary detection signal emitted by the SQUID device so as to supply an analog acquisition signal. The main detection antenna is of the volume type, comprising a Helmholtz coil or a saddle coil, or more complex volume geometries, in particular gradiometer geometries, and the step of processing the secondary detection signal comprises a flux-locked loop, the flux-locked loop being arranged to linearize the response of the SQUID device.

Description

TECHNICAL FIELD

[0001] The present invention relates to a SQUID-based low-noise RF detection and acquisition system. The present invention also relates to an equipment item comprising this system, in particular a magnetic resonance imaging equipment. BACKGROUND

[0002] It is well known to use a SQUID-based (for "Superconducting Quantum Interference Device") detection system in a magnetic resonance imaging (MRI) equipment.

[0003] During an MRI experiment, the subject is placed in a fixed and uniform magnetic field B0. The sample is then subjected to an RF frequency signal ω, which is tuned to the Larmor frequency ω0= γB0of the protons in the field B0, with γ / (2π) = 42.6 MHz. -1 The gyromagnetic ratio of the protons. After this excitation, the sample emits a frequency signal ω0picked up by the detection system, the principle of which in modern commercial equipment is based on a cooled induction antenna.

[0004] The usual MRI paradigm is to choose the highest possible magnetic field for two reasons:

[0005] - The first reason is that a higher field makes it possible to bias a larger number of protons, which leads to more signal and thus to a reduced experiment time and a finer image resolution.

[0006] - The second reason is that conventional RF detection is done by an induction antenna, the sensitivity of which is proportional to ω.

[0007] By considering the thermal noise level in ω 1 / 4 , the only detection of a Faraday antenna follows the law ω -3 / 4 Since ω is proportional to the working field B0, working at a high field makes it possible to reduce the detection threshold. Typical clinical MRI equipment works at 1 T, 5 T or 3 T. Certain models reach 7 T and experiments aim to reach 11 T, 7 T.

[0008] However, increasing the field generates ionic noise in the sample, reduces the image quality due to the differences in the magnetic susceptibility of the tissues, and tends to make the contrast level, not to mention the usual constraints associated with high fields: production and maintenance of expensive superconducting coils, magnetic shielding of the MRI coils, impossibility of performing MRI on people with cardiac stimulators or pacemakers, impossibility of performing MRI on soldiers wounded by bullets.

[0009] Document CN105137374A discloses an MRI device with nanometer resolution SQUID detection, which implements a magnetic resonance imaging method and an ultra-high resolution apparatus. The method comprises at least one of the following steps: a step of placing a measured sample within a working range of a magnetic field gradient source and a nano superconducting quantum interference device; a step of using a static magnetic field source to apply a static magnetic field to the measured sample, and using a radio frequency source to apply a nuclear magnetic resonance radio frequency pulse to the measured sample to excite the measured sample so as to generate nuclear magnetic resonance; a step of using the nano superconducting quantum interference device to directly couple the measured sample to detect a nuclear magnetic resonance spectrum signal generated by the measured sample; and a step of establishing an image of the measured sample according to the detected nuclear magnetic resonance spectrum signal and spatial distribution information of the magnetic field gradient source. The nano superconducting quantum interference device is used as a detector, magnetic resonance imaging with nanometer resolution can be performed, measurement is not disturbed by vibration and electric field signals, the sample can be directly coupled with the detector at a close distance, the imaging range is increased, and work in a strong magnetic field is performed.

[0010] Document JP2010256318A discloses high resolution proton nuclear magnetic resonance equipment and imaging (NMR / MRI) via a magnetic flux transformer in microtesla magnetic fields at high critical temperature (high Tc) using a superconducting quantum interference device (SQUID). The invention relates to a method and apparatus. The SQUID and input coil are mounted in a superconducting can that protects from environmental noise and brings the SQUID into a stable operating state. NMR signals can be maintained even when the sample is far from the SQUID detector.

[0011] Document CN1287160C discloses NMR and MRI equipment with SQUID detection, with pre-polarization, in which nuclear magnetic resonance (NMR) signals are detected in microtesla fields. After pre-polarization in a millitesla field, detection is performed by an untuned direct current superconducting quantum interference device magnetometer (SQUID).

[0012] Document WO2006052236A1 discloses NMR and MRI equipment with SQUID detection, with pre-polarization and a Faraday main antenna. Magnetic resonance imaging in an extremely low magnetic field is based on extremely low field NMR. A gradient magnetic field is applied and an image is constructed from the detected NMR signals.

[0013] These SQUID-based detection and acquisition equipment have the disadvantage of requiring a pre-polarization method and employ high Tc SQUIDs.

[0014] The document "A compact SQUID-detected magnetic resonance imaging system under microtesla field in a magnetically unshielded environment" by Chen Hsin-Hsien et al., Journal of Applied Physics, American Institute of Physics, Volume 110, Number 9, 1 November 2011 (2011-11-01) discloses a system for SQUID-based radiofrequency detection and acquisition, which is specifically set to be integrated in a nuclear magnetic resonance apparatus, the detection system comprising a main detection antenna, a flux transformer having a primary winding connected to the main detection antenna, a SQUID device, a cryogenic device set to cool the SQUID device and the flux transformer, a step of processing the secondary detection signal emitted by the SQUID device, the processing step comprising a flux-locked loop and being set to deliver an analog acquisition signal.

[0015] The document US2013271142A1 discloses low-field SQUID MRI components and methods. They include a low-field portable MRI instrument (SQUID) to be used under the bed and a SQUID-based portable MRI system. The MRI instrument implements a second-order superconducting gradiometer suitable for use with a low-field MRI device.

[0016] The aim of the present invention is to propose a low-noise RF-based detection and acquisition system, which is simpler and cheaper to design than the systems of the preceding prior art and which specifically improves the performance in terms of signal-to-noise ratio. SUMMARY

[0017] The aim is achieved by a system for SQUID-based radiofrequency (RF) detection and acquisition, which is specifically set to be integrated into a nuclear magnetic resonance apparatus (MRI or NMR), comprising:

[0018] - a main detection antenna of the volume type,

[0019] - a flux transformer having a primary winding connected to the main detection antenna,

[0020] - a SQUID device arranged to capture the magnetic flux captured by the main antenna and reproduced within the SQUID device via the flux transformer by the input winding, and to deliver a secondary detection signal,

[0021] - a cryogenic device designed to cool the SQUID device,

[0022] - a step of processing the secondary detection signal emitted by the SQUID device to deliver an analog acquisition signal, comprising a flux-locked loop (FLL) arranged to linearize the response of the SQUID device.

[0023] According to the invention, the SQUID device is of the low critical temperature type, the low temperature device being further arranged to cool the flux transformer, and the primary detection antenna is of the volume type and has an open geometry.

[0024] The primary detection antenna can thus comprise a Helmholtz coil, a saddle coil, or a gradiometer geometry with 1st, 2nd or higher order. These volume antennas can be tuned to the signal to be detected, or not.

[0025] Operating at low magnetic fields of about 1 mT or less also makes it possible to benefit from a sharp increase in contrast T1, opening the way to unique imaging possibilities into the low field mode. This fact is described in detail in the publication "SQUID-detected MRI at 132 μT with T1 -weighted contrast established at 10 μT - 300 mT" by S. K. Lee et al., published in the journal "Magnetic Resonance in Medicine", vol. 53-1, January 2005, pages 9-14.

[0026] The flux-locked loop (FLL) can advantageously comprise a low noise amplifier (LNA), which can comprise a semiconductor heterostructure amplifier or a SQUID-based amplification system. A SQUID-based amplification system is proposed in the document US2013271142A1. To implement these techniques in the context of the present invention, it can be useful to refer to the book "The SQUID Handbook: Fundamentals of Technology and Applications of SQUIDs and SQUID systems" by John Clarke, Wiley-VCH 2004.

[0027] The detection and acquisition system according to the invention can also comprise one or more active noise compensation coils for the noise external to the system.

[0028] The detection and acquisition system according to the invention can also comprise one or more passive shielding screens of the system. Such passive shielding can be magnetic in nature, in particular via ferrite, high permeability alloys, or any other material or alloy of high magnetic permeability. The shielding can also be made of metal, for example copper or aluminum.

[0029] In a preferred version of the application, the main detection antenna cooperates with the flux transformer to concentrate the flux captured by the SQUID device.

[0030] It is also proposed that the detection and acquisition system according to the application further comprises, within the flux transformer, an inductive feedback coil arranged to react to variations in the input flux in order to maintain the SQUID device at its maximum flux sensitivity level.

[0031] According to another aspect of the application, it is proposed an item of magnetic resonance imaging (MRI) equipment comprising: a SQUID-based RF detection and detection system (B) according to the application, an antenna holder device (A) integrating the main detection antenna of the volume type and connected to said detection and acquisition system (B), and an analog-digital conversion stage (C) arranged to convert the analog acquisition signal into digital data suitable for being post-processed for the purpose of generating and displaying MRI images.

[0032] The MRI equipment can be coupled, for example, to a magnetoencephalography device (MEG).

[0033] The SQUID-based RF detection and acquisition system can be implemented in a nuclear magnetic resonance (NMR) equipment, or in a SQUID-based magnetic sensor device for metal prospecting, in order to detect radiofrequency (RF) waves emitted by a metal vein in response to the emission of radiofrequency (RF) waves in the ground.

[0034] The ultra-sensitive RF sensor equipment can also be arranged to comprise a detection and acquisition system according to the application, or an item of radio astronomy equipment operating in the radiofrequency (RF) domain comprising a SQUID-based RF acquisition and acquisition system according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0035] The application can be better understood with reference to the accompanying drawings described below:

[0036] · Figure 1 is a diagram of the RF detection and SQUID-based signal processing circuit.

[0037] · Figure 2 is a schematic diagram of an MRI acquisition according to the RF detection application described herein.

[0038] · Figure 3 several main detection antenna geometries are shown. DETAILED DESCRIPTION

[0039] Reference will now be made to Figure 1 An embodiment of a SQUID-based RF acquisition and acquisition system 1 according to the application will now be described.

[0040] The SQUID-based RF detection and acquisition system 1 includes: a main inductive antenna 5, which has a volume type, is manufactured in the form of a Helmholtz coil or a saddle coil, or has any other type of volume (specifically, a gradiometer), and, when the antenna is in resonance, the main inductive antenna is connected via a capacitor C. a The coupling capacitor 9 is connected to the primary winding 6 with inductance L1; the flux converter 2, which has a secondary winding 7 with inductance L2, is connected in series with the entrance coil 8 with inductance Li, which generates the flux captured by the SQUID device 3.

[0041] If the antenna is not resonant, then the capacitor is absent and antenna 5 is directly connected to the primary winding 6.

[0042] Flux converter 2 and SQUID device 3 are kept at a low temperature in a cryogenic device (not shown), which includes pulse tubes (such as those made by...). The product sold is PT403.

[0043] Step 4, processing the secondary detection signal, includes a preamplifier 40 (LNA) measuring a voltage at a terminal of the SQUID device 3. This voltage measurement represents the detection signal, which is applied to the input of a flux-locked loop circuit 41, which includes a low-noise amplifier and is connected to an inductor L... feed The feedback coil 10 is designed to respond to changes in incoming flux in order to maintain the SQUID device 3 at its maximum flux sensitivity level. A method for a flux-locked loop is disclosed in document US20120206136A1.

[0044] The following are examples of SQUID-based RF acquisition and acquisition of quantitative features of System 1:

[0045] - Typical time width of the wave train to be detected: T2 * ~50ms

[0046] - The center frequency of the main antenna is ω0~40kHz

[0047] -Main bandwidth Δω~20kHz

[0048] -Main quality factor Q ~ 2 (if it is a resonant antenna)

[0049] -Magnetic field strength B at the main antenna p Approximately one hundred fT to pT

[0050] -SQUID's input coil inductance L i =720nH

[0051] -Specific inductance of the main antenna

[0052] - the resistance R of the main antenna a = 1 Ω.

[0053] - the resonant capacity C of the main antenna a = 6 μF.

[0054] Induction antenna

[0055] The volume type geometry is chosen for the antenna 5, taking into account the targeted application. Examples of such geometries include a Helmholtz coil, a "saddle" coil or other more complex geometries, in particular a gradiometer geometry. Such a geometry makes it possible to collect the highest possible signal while allowing relative comfort for the patient by its open geometry. The Faraday main antenna 5 must be tuned to the MRI signal. This antenna 5 has a self-induction L a , the self-induction, the resistance will be sought to be reduced as much as possible in order to minimize the Johnson-Nyquist noise in the antenna.

[0056] The parameters L a , R a are fixed by the chosen antenna geometry and the type of material constituting the antenna. The antenna can then be made to resonate, which allows two things:

[0057] - the quality factor Q of the resonant antenna makes it possible to naturally amplify the detected signal,

[0058] - the bandwidth Δω of the antenna makes it possible to filter the captured signal and reject electromagnetic noise outside the frequency band Δω of interest.

[0059] This implementation is valid for both resonant and non-resonant antennas. The case of a resonant antenna is explained below.

[0060] The capacity is set so that the natural frequency of the antenna is tuned to the frequency of the received signal ω0≈ 40 kHz. Furthermore, the antenna design must take into account its bandwidth Δω a = R a / L a , which is expected to be of the same order of magnitude as the bandwidth width Δω of the RF signal in order not to lose information when limiting the detected noise. Thus, based on the desired frequency characteristics, the value of the self-induction L a of the antenna 5 will determine the ability to select the resistance.

[0061] The main induction antenna 5 is a volume antenna. For example, a saddle-shaped Helmholtz geometry antenna can be chosen, or any other more complex volume geometry, in particular a gradiometer geometry.

[0062] Figure 3Two of these geometries of volumetric antennas implemented in the RF detection and acquisition system according to the application are shown.

[0063] The first geometry (a) is of the saddle type, the performances of which, in particular in terms of spatial uniformity, are well known to the person skilled in the art. The diameter of a saddle antenna is equal to 1.5 times its length.

[0064] The other geometry (b) is a first order gradiometric version of the saddle. This volumetric antenna 5' is composed of two sub-antennas 51, 52 mounted in series with each other. The first, internal antenna 51 has a saddle geometry and has, in this example, two turns of wire. The second, external and larger antenna 52, also of saddle geometry, has a single turn of wire. The dimensions of the system and the orientation of the wires are chosen so that:

[0065] - the external and internal parts of the antenna have the same inductance. This is allowed by the two turns of wire in the internal antenna.

[0066] - the current in the internal part circulates in the opposite direction to the current in the external part.

[0067] With this configuration, the gradiometric antenna (saddle) 5' makes it possible to suppress the noise from sources located at a great distance in front of the dimensions of the antenna 5', while benefiting from the uniformity properties of the saddle geometry. The principle of gradiometric antennas is described in detail in the article "Superconducting quantum interference device instruments and applications" by R.L. Fagaly, Review of Scientific Instruments, 77, 101101 (2006).

[0068] Flow concentration and optimal inductance

[0069] To determine the inductance of the antenna, reference is made to Figure 1 The rest of the detection system is studied. The SQUID device 3 used (for example model SQ680 from StarCryo) is coupled to an input coil 8 with an inductance L i = 720 nH via a flux transformation system 2 embodied by coils L1 and L2 coupled by inductance. The current flowing in the antenna 5 (respectively coil L2) is denoted i1 (respectively i2) and the flux captured by the antenna 5 is denoted Φ a . In addition, the mutual inductance of the input coil - SQUID is denoted and is the mutual inductance between coils L1 and L2.

[0070] k and k ！ are dimensionless factors, and Ls is the self-induction of the SQUID device 3. The goal is to capture the external flux Φ a and the flux Φ sq captured by the SQUID 3.

[0071] The inductive coupling relationship in the circuit is written as:

[0072] Φ a + M 12 i2= (L a + L1)i1 (1)

[0073] (L2+ L i )i2= M 12 i1 (neglecting the effect of the current flowing through the SQUID) (2)

[0074] Φ sq = M is i1 (3)

[0075] By combining these equations, the following is obtained:

[0076]

[0077] This latter equation establishes the link between the external excitation given by Φ a and the response level of the SQUID 3 quantified by Φ sq . It is thus understood why such a component is called a "flux concentrator": the main role of the Faraday antenna 5 is to increase the flux captured by the SQUID 3.

[0078] To reach the maximum sensitivity level of the device, for a given Φ a , the maximum response in Φ s is given by:

[0079]

[0080] The resistance of the main antenna 5 is set to a reasonable value, for example R a = 1 Ω. To comply with a bandwidth value of the order of ten kH, it is thus necessary to ensure that L a = 0.1 mH. This value of L a sets the value of the capacitor:

[0081]

[0082] The ratio of the inductances L1 and L2 is thus required:

[0083]

[0084] i.e. L1 1390L2. By the coupling constant k！ The precise values of L1 and L2 are set, the coupling constant should be as close to 1 as possible in order to ensure the maximum sensitivity of the device.

[0085] Flux transition requirements

[0086] It can be reasonably questioned why the inductive coupling has been chosen from the coils L1 and L2. It would be simpler to connect the antenna directly to the input coil of the SQUID 3. Assuming that the flux transformer 2 comprising the coils (L1) and (L2) does not exist, and that the inductive antenna with the inductance L a is connected in series with the input coil (L i ) of the SQUID. The magnetic coupling is then written as

[0087] Φ a = (L a + L i )i1 (9)

[0088] The coupling is thus introduced to the SQUID Φ sq = M is i1

[0089]

[0090] The above equation shows that the maximum sensitivity is reached for the inductance of the antenna 5 by making it equal to the inductance of the input coil 8 of the SQUID 3: L a = L i .

[0091] The inductance of the antenna 5 can be adjusted, for example, by adjusting the number of turns in the loop or by adjusting the geometry of the antenna.

[0092] The need to introduce a flux transformer is then understood. Indeed, in the absence of the latter, the inductance of the antenna is imposed on the value L a = L i = 720 nH. This inductance value imposes a resistance on the antenna.

[0093] R a = LΔω = 0.72 mΩ (11)

[0094] and a capacitor connected to the antenna with the following values

[0095]

[0096] These results are not satisfactory for two reasons. On the one hand, the capacity found is very high; for these values, chemical capacitors that cannot adapt to the cold of the cryostat should be used. On the other hand, the value of the resistance is very low, which will have an impact on the intensity noise in the antenna.

[0097]

[0098] That is, the antenna is cooled to 100K, δi a ≈3nA / √Hz. This is approximately equivalent to the input of SQUID. The noise level is very low; it is too high.

[0099] One solution is to increase the resistance of the main antenna 5, which requires passing it through the flux converter 2 to accommodate the inductor in order to maintain the same bandwidth.

[0100] SQUID current reader

[0101] The SQUID device 3 used is a cryogenic cooler (e.g., from...) PT 403) cooling low Tc SQUID (e.g. from PT 403) (SQ680) and by current i p Bias.

[0102] Unlike its high-Tc counterpart, the low-Tc SQUID has a much lower thermal noise level, which allows for a significant increase in signal-to-noise ratio and ultimately, improved image quality. This is achieved by reading the current generated in the input coil at a noise level of 0.8 pA / √Hz. Therefore, this noise level is the target for addressing thermal noise in the inductive antenna.

[0103] Low noise amplifier - FLL

[0104] The SQUID device has a nonlinear, periodic current-captured flux response with a quantum flux period of Φ0 = h / 2e. To linearize this response and avoid artifacts that degrade image quality, the SQUID 3 is coupled to a flux-locked loop (FLL), an example of which is described below.

[0105] The circuit first has a preamplifier 40 (LNA) that measures the voltage at the terminals of the SQUID.

[0106] For an amplification system, two options are conceivable: choose to amplify using a squid, as in the case of, for example, US2013271142A, or use an ASIC-type semiconductor heterostructure amplification, which may be more advantageous but also imposes more constraints, specifically on the maximum voltage oscillation level of the input signal.

[0107] With inductance L feed The feedback coil 10 allows for a response to changes in input flux in order to maintain the SQUID 3 at its maximum flux sensitivity level. The signal is read at the output of the flux-locked loop.

[0108] MRI equipment

[0109] The SQUID-based ultra-sensitive detection and RF acquisition system can be integrated into MRI equipment using an operating magnetic field of about B0= 1 mT (which corresponds to a frequency ω0 40 kHz), while maintaining the acquisition times and image quality according to current clinical standards. The operating magnetic field reduction by several orders of magnitude makes it possible to eliminate the constraints, thus preventing, on the one hand, the massive adoption of MRI as an imaging standard, and on the other hand, opening up still non-existent applications, such as an MRI on board a truck for the diagnosis of the type of stroke (ischemic or hemorrhagic), 100% MRI screening of breast cancer (by CT scan) or intraoperative MRI, thanks to a light equipment without magnetic shielding which is not very expensive.

[0110] Figure 2 A schematic diagram of an MRI experiment carried out by the detection system according to the present application is shown. A knee MRI has been chosen, the bone joint imaging being one of the first possible applications of the present application. The patient's knee is inserted into a cylinder a which comprises a solenoid and the above-mentioned receiving antenna, the solenoid ensuring the presence of a permanent magnetic field B0≈ 1 mT uniformly present at about 10 ppm within a volume of about 10 x 10 x 10 cm3 of the gradient. The receiving antenna is cooled to a temperature of about 60 K using a custom cryogenic system derived from a pulse tube, thus ensuring the cooling of the SQUID system of the portion B. 3

[0111] The portion B comprises SQUIDs which ensure the reading of the current coming from the inductive antenna, and the processing electronics of the above-mentioned signal, the preamplification system, and the flux-locked loop FLL composed of an integrator amplifier, a reading resistor and a toroidal coil L feed The entire stage is cooled at a temperature close to 4.2 K using a cryogenic machine (for example a PT403 pulse tube from CryoMech).

[0112] The portion C provides the analog-digital conversion of the signal for computer post-processing in order to control the equipment and display the MRI images obtained.

[0113] Medical applications

[0114] The sensitivity and portability of the device make it interesting first of all for magnetic resonance imaging (MRI). The high level of contrast obtained at low field makes the technique interesting for diagnoses in which the contrast is currently insufficient with high-field technology.

[0115] ​Moreover, the equipment according to the present application can be easily installed in an ambulance in order to quickly diagnose an ischemic or hemorrhagic stroke at the scene of an accident, in order to more quickly care for the patient and avoid irreversible damage to cognitive abilities.

[0116] Due to its low cost and ease of use, the imaging equipment according to the present application can also be widely extended in use cases in which it is not used today: screening for breast cancer in women over 50 years of age, for neurology and psychiatry: early screening of diseases such as schizophrenia, depression or epilepsy; screening for prostate cancer.

[0117] Finally, many low-field MRI projects also have the purpose of designing hybrid MRI-Magnetoencephalography (MEG) devices. Reference is made to the source

[0118] https: / / www.aalto.fi / en / department-of-neuroscience-and-biomedical- engineering / meg-mri-brain-imaging-group Nuclear magnetic resonance This is the case of the work of the Aalto University of Finland.

[0119] The SQUID-based MRI equipment project according to the present application can be adapted to integrate a MEG device therein.

[0120] Mining

[0121] NMR devices, in particular for chemical characterization, can also benefit from the detection system described herein in order to design lighter and cheaper equipment, for similar reasons to those given for MRI.

[0122] Military

[0123] In the mining industry, there are already SQUID-based magnetic sensors for detecting metals, as shown in the document US 7,394,250. The detection system described herein, due to its very low noise level, can also be integrated in such devices for mining. The principle is as follows: RF waves are emitted in the ground, and if there is a metal vein, eddy currents are induced in the vein, which in turn emit RF waves, which are detected by the device described herein, which integrates the detection system with SQUIDs.

[0124] Radio astronomy

[0125] Ultra-sensitive radio frequency sensors are well-known elements of electronic weapon systems: they are used, for example, to detect communication signals. Another advantageous application is the detection of underwater submarines: since submarines are composed of ferromagnetic materials, the device described herein is able to detect their presence by emitting RF waves and detecting the waves generated by the induced eddy currents, according to the same principles as prospecting. At the same time, other systems detect the perturbation of the local earth field generated by the passage of underwater vehicles, as shown in the document "Magnetic detection of a surface ship by an airborne LTS SQUID MAD" by Megumi Hirota et al., published in IEEE Transactions on Applied Superconductivity 11 (1): 884-887, April 2001.

[0126] ​

[0127] SQUID-based systems have been widely used in the field of radio astronomy, for example integrated into superconducting bolometers for reading and / or amplifying very low currents. Due to their very high sensitivity, the system described herein can find interesting integration in calibrated telescopes in the RF domain.

[0128] Of course, the present application is not limited to the implementation already described and many other alternative implementations can be envisaged within the scope of the present application.

Claims

1. A system for SQUID-based radiofrequency detection and acquisition, arranged to be integrated into a nuclear magnetic resonance apparatus, comprising: - a volume-type main detection antenna (5), - a flux transformer (2) having a primary winding (6) connected to the main detection antenna (5), - a SQUID device (3) arranged to capture the magnetic flux captured by the main detection antenna (5) and reproduced within the SQUID device via the flux transformer (2) by an input winding (8) and deliver a secondary detection signal, - a cryogenic device designed to cool the SQUID device (3), - a step (4) of processing the secondary detection signal emitted by the SQUID device (3) to deliver an analog acquisition signal, including a flux-locked loop arranged to linearize the response of the SQUID device (3), characterized in that the SQUID device is of the low critical temperature type, the cryogenic device is also arranged to cool the flux transformer, and in that the main detection antenna (5) is of the volume type and has an open geometry and includes a Helmholtz or saddle coil.

2. The system for radio frequency detection and acquisition of claim 1, wherein, The main detection antenna is a gradiometer antenna.

3. The system for radio frequency detection and acquisition of claim 1, wherein, The flux-locked loop includes a low-noise amplifier.

4. The system for radio frequency detection and acquisition of claim 3, wherein, The low-noise amplifier includes a semiconductor heterostructure amplifier.

5. The system for radio frequency detection and acquisition of claim 3 or 4, wherein, The low-noise amplifier includes a SQUID-based amplification system.

6. The system for radio frequency detection and acquisition of claim 1, wherein, The radiofrequency detection and acquisition system also includes one or more active noise compensation coils for noise external to the system.

7. The system for radio frequency detection and acquisition of claim 1, wherein, The main detection antenna (5) cooperates with the flux transformer (2) to concentrate the flux captured by the SQUID device.

8. The system for radio frequency detection and acquisition of claim 1, wherein, The radiofrequency detection and acquisition system also includes an inductive feedback coil (10) within the flux transformer (2) arranged to react to variations in input flux in order to maintain the SQUID device (3) at its maximum flux sensitivity level.

9. A magnetic resonance imaging apparatus comprising: - a radiofrequency detection and acquisition system according to any one of claims 1 to 8, - an antenna holder device integrating the volume-type main detection antenna and connected to the radiofrequency detection and acquisition system, - an analog-digital conversion stage designed to convert the analog acquisition signal into digital data suitable for post-processing to generate and display a magnetic resonance imaging image.

10. The magnetic resonance imaging apparatus of claim 9, characterized by The magnetic resonance imaging apparatus is coupled to a magnetoencephalography device.

11. A nuclear magnetic resonance apparatus comprising a radiofrequency detection and acquisition system according to any one of claims 1 to 8.

12. A SQUID-based magnetic sensor apparatus for metal prospecting, comprising a radiofrequency detection and acquisition system according to any one of claims 1 to 8, for detecting radiofrequency waves emitted by a metal vein in response to the emission of radiofrequency waves in the ground.

13. An ultra-sensitive radio-frequency sensor apparatus comprising the system for radio-frequency detection and acquisition according to any one of claims 1 to 8.

14. A radio astronomy apparatus operating in the radio-frequency domain comprising the system for radio-frequency detection and acquisition according to any one of claims 1 to 8.

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