Apparatus and method for performing magnetic resonance imaging of metallic or partially metallic components, and application of the method to imaging electrochemical cells.

Abstract

The present invention relates to a magnetic resonance imaging (MRI) apparatus (1) designed to image essentially metallic components, comprising means (b") for generating a polarizing magnetic field intended to be applied to the component (a), radio frequency (RF) means (g) for exciting the component (a), detection means cooperating with the antenna means for delivering a magnetic resonance imaging (MRI) signal, and means for processing the MRI signal to provide characteristic information about the state of the component (a). The component (a) is subjected to a very weak magnetic field of less than 10 mT, and the detection means comprises a pickup coil (h) magnetically coupled to the polarizing means (b") and the radio frequency means (g) and acting as a magnetic flux concentrator, and a SQUID (Superconducting Quantum Interference Device) detector located downstream of the pickup coil (h) via a transformer.

Description

[Technical Field]

[0001] This specification describes an apparatus for performing magnetic resonance imaging of metallic or partially metallic components. This specification also includes a method for imaging metallic or partially metallic components implemented in this apparatus, and its application to imaging electrochemical cells, particularly lithium-ion cells. [Background technology]

[0002] Magnetic resonance imaging (MRI) is based on the principle of nuclear magnetic resonance (NMR). This phenomenon utilizes the resonance between two energy levels that occurs when a quantum magnetic moment (spin) is subjected to an external magnetic field. This spin can be that of an electron or an atomic nucleus. In the case of medical NMR, the target nucleus is almost always hydrogen (which has only one proton) present in water, fat, or human tissue.

[0003] NMR (or MRI) experiments are performed in several precise steps. First, the sample (in imaging of a lithium-ion cell or any metal component, this is the component itself) is placed in a very uniform static magnetic field B0 called a polarization field, generated by a large superconducting coil. In most commercially available instruments, this field varies from 1.5 T to over 10 T. Once the sample protons are placed in the field B0, they precede this field at a frequency ω0 given by ω0 = γB0, where γ is called the gyromagnetic ratio.

[0004] Next, the protons are excited by a high-frequency signal having the same frequency ω=ω0 as the proton precession. This excitation de-precesses the protons, and after a while, they slowly decay and return to their original precessional state, emitting a signal that can be detected by an antenna. Measuring this signal is a means of collecting information about the composition of the body and ultimately reconstructing an MRI image.

[0005] The overall principle of MRI experiments can be summarized as follows: - The body part to be imaged is placed in a static, uniform magnetic field B0. -When placed in this magnetic field, protons lead with frequency ω0 = γB0. - The excitation antenna is used to transmit pulses of intensity B1 and frequency ω=ω0 that are tuned to the precession of protons. - Protons are sent to higher energy states, transmitting signals of intensity B2 and frequency ω0, then decay and return to their original states. More importantly, this signal decays over a typical time τ1 corresponding to the recovery of longitudinal magnetization in the direction of B0, and a typical time τ2 corresponding to the loss of spin-spin coherence in the sample. These typical time constants are characteristics of the precise state at each point in the sample and are used to generate contrast within MRI images. In medical MRI, they provide information about the type of tissue (water, fat, muscle, etc.) at a particular point.

[0006] To construct an MRI image, it is necessary to determine the origin of the signal detected by the MRI antenna. For this purpose, a gradient coil is used. In addition to a permanent and uniform magnetic field B0, a small auxiliary magnetic field δB(x,y,z) that changes linearly along three directions in space is added.

[0007] Typically, in an MRI device with a magnetic field of 5T, 100mT.m -1 An additional magnetic field δB of the order of is observed. Since the resonance frequency of the nucleus is proportional to the local magnetic field, the resonance frequency and phase of the signal can be spatially encoded using the gradient magnetic field, thereby forming a 3D image.

[0008] During the MRI sequence, these gradient magnetic fields change rapidly on a millisecond timescale to selectively excite specific parts of the sample. The models selected to apply the gradient and excitation pulses constitute the MRI sequence.

[0009] Different sequences allow for the display of different contrasts and enable the viewing of different things. In medical MRI, a wide variety of sequences exist, some adapted for viewing blood vessels (time-of-flight sequences), others better suited for functional imaging (BOLD, representing "blood oxygenation level-dependent"), and more common T1 or T2 weighted sequences that can distinguish fat, organic tissue, tumors, and so on.

[0010] It should be noted that MRI sequences function as image constructs in inverse Fourier space (or k-space), and different MRI sequences respond to different acquisition trajectories.

[0011] Next, we will explain why it is necessary to use low-field MRI to image metal samples.

[0012] For over 40 years, innovation in MRI has consistently moved towards higher magnetic fields. Higher magnetic field strength means that more nuclei in the sample are polarized, resulting in a higher signal-to-noise ratio. Furthermore, since the detection frequency is proportional to the magnetic field, it becomes possible for typical inductive detection antennas to operate at higher frequencies in a range where they are inherently more sensitive. In short, higher magnetic field strength means better resolution and shorter acquisition times. However, this strategy has obvious drawbacks. Commercial high-field machines require heavy and expensive superconducting magnets cooled to 4 Kelvin with liquid helium and require costly maintenance. A typical 1.5T scanner costs nearly $1 million upfront, plus hundreds of thousands of dollars per year for maintenance. MRI units must be installed in a dedicated, magnetically shielded room with a reinforced floor. This makes MRI technology a larger imaging procedure than ultrasound or CT.

[0013] A less-known problem with high-field MRI is the inability to image metal samples, let alone images them in the presence of metal. This is a double problem. Having a sample that contains both metallic and non-metallic parts means there are large local differences in magnetic susceptibility. This causes magnetic field gradient artifacts that disrupt the linearity of the gradient magnetic field pattern used to perform MRI. - High-frequency magnetic fields cannot penetrate most metal samples due to the skin effect of conductors.

[0014] When a propagating electromagnetic field reaches the conductor / dielectric interface, eddy currents are generated within the inductor. These eddy currents then generate another magnetic field to compensate for the emerging magnetic field. As a result, the entire magnetic field effectively dissipates once it enters most of the conductive sample. The penetration depth δ is a measure of how deep the magnetic field can penetrate into the interior of a metallic sample.

number

[0015] In the formula, ω is pulsation, ρ is DC resistivity, μ0 is vacuum permeability, and μ r This is the relative permeability of the sample.

[0016] In the case of proton MRI, γ H / (2π):42MHz.T -1 And in the case of lithium, this number is γ Li / (2π):16.5MHz.T -1 It is slightly lower. In either case, this means that in conventional high-field MRI, the excitation frequency used is on the order of 30 MHz or higher. For this reason, the penetration depth in most metals is typically less than 100 μm, making MRI of metal samples impossible. The table below summarizes the typical resistivity and penetration depth associated with typical metals used in lithium-ion cell compositions or packaging. [Table 1]

[0017] Conventional high-field machines operate at magnetic fields in the range of 1 T to over 10 T. Based on lithium, this encompasses frequencies from 25 MHz to over 170 MHz. In the above table, this corresponds to a penetration depth of a fraction of a micron and it can be seen that it makes high-field MRI impossible for metallic samples.

[0018] Therefore, in order to operate at lower frequencies, it is necessary to reduce the magnetic field. Also, this means a lighter and lower-cost machine that does not require extensive maintenance or magnetic shielding and is not affected by susceptibility artifacts. However, simply reducing the magnetic field using a conventional machine results in a much lower SNR (signal-to-noise ratio), which means that the image quality deteriorates and the acquisition takes more time.

[0019] One possible solution is to use a SQUID (which stands for "superconducting quantum interference device"), which is an ultrasensitive magnetometer that makes it possible to reduce the magnetic field of an NMR experiment while retaining an SNR sufficient to generate images with good resolution and contrast within a reasonable time. Using this technology, MRI images can be created at magnetic fields in the range of 100 μT to a few mT. Based on lithium, this means NMR frequencies in the range of 1.6 kHz to about 20 kHz. Looking at the table, this means a penetration depth in the range of a few millimeters to 1 cm depending on the metal, making it possible to image metallic samples.

[0020] One example is the work of the team of Alexej Jerschow at New York University. To avoid problems related to high frequencies and skin effects, this team devised a technique called inverse MRI (ioMRI, representing "IntraOperative Magnetic Resonance Imaging") [6][7]. This technique is described in detail in a very recent book by Haber-Pohlmeier, Bliimich and Ciobanu

[12] . Instead of creating a direct image of the lithium-ion cell, it is the idea of using MRI of the cell's surrounding environment to perform an indirect measurement of the local magnetic susceptibilities of the anode and cathode. More precisely, the cell is placed in a holder containing a measurement medium surrounding the lithium-ion cell, usually doped water. Then, a permanent magnetic field B0 is applied to the cell. The cell then generates a secondary magnetic field B proportional to the local magnetic susceptibilities of the cell components, and this secondary magnetic field is mapped with a special MRI sequence of the surrounding doped water. For a schematic of the layout of this device, see Illot et al. 2018 [7], [Figure 1].

[0021] By accurately measuring this secondary magnetic field during operation, it is possible to estimate the overall magnetic susceptibilities of the anode and cathode. This overall magnetic susceptibility is then shown in [Figure 2] by Ilott et al. 2018 [7] as being related to the SOC (state of charge). This figure shows the overall magnetic susceptibility measured as a function of the state of charge.

[0022] The sensitivity of the anode or cathode (in ppm) increases by approximately 50% from a fully discharged state to a 250 mAh charge. The magnetic field map (in ppm) is given relative to a fully charged cell. The cells used were manufactured by the Rochester Institute of Technology (RIT). Figure 4 in reference [7] also shows that the magnetic field map can be used to classify cells into different defect categories, e.g., bent, small clumps. In this figure, the magnetic field map is given in ppm for the magnetic field value of one of the defect-free cells. The mean and standard deviation of the topographic map taken across the entire photograph are also shown. The MRI sequence used was initially a simple FLASH sequence, followed by specific point imaging with T1 weighting to account for susceptibility artifacts.

[0023] While ioMRI demonstrates that MRI can indeed be effectively used to diagnose state of charge (SOC) and state of health (SOH), it suffers from a major drawback: it only provides a global map of the anode or cathode state and cannot create spatially resolved maps of the local SOC and SOH for each electrode.

[0024] On the other hand, to date, SQUID MRI has not seen any breakthroughs due to the lack of usable signal-to-noise ratio (SNR) at low magnetic fields. To increase the SNR, most attempts have used a technique called pre-polarization. First, a high pulsed field of about 100 mT is applied to increase the Boltzmann polarization of the sample, which increases linearly with the magnetic field. Then, the magnetic field is rapidly reduced, and MRI acquisition is performed at a target magnetic field of typically about 100 μT.

[0025] This allows us to take advantage of both the moderately high polarization at 100 mT and the advantages associated with ultra-low magnetic fields, primarily improved contrast and reduced constraints on magnetic field uniformity. However, pre-polarization requires heavy machinery to generate a pulsed field and complex shielding to cancel out noise caused by eddy currents. More importantly, the rapid switching of the magnetic field makes this technique impractical on metallic samples.

[0026] The paper

[28] , Moszle M et al: "SQUID-detected microtesla MRI in the presence of metal", Journal of Magnetic Resonance, vol.179, No.1, March 1, 2006, pp. 146-151, XO024919553, discloses a magnetic resonance imaging apparatus and method with SQUID detection of organic components in the presence of metal. Using this method, the authors were able to image an organic sample, in this case a bell pepper, enclosed in a 200 μm thick aluminum case or surrounded by 20 μm thick aluminum foil, as shown on page 149. [Overview of the Initiative]

[0027] However, state-of-the-art imaging equipment cannot perform magnetic resonance imaging of metal parts with image quality sufficient for industrial use.

[0028] The objective of the present invention is precisely to improve the above limitations by providing an apparatus for MRI imaging of metal parts that can provide spatially resolved mapping thereof.

[0029] (Disclosure of the invention) This objective is achieved by a magnetic resonance imaging (MRI) device configured to perform imaging of substantially metallic components, but that device, -Means for generating a polarization magnetic field intended to be applied to a substantially metallic component, - A high-frequency means for substantially exciting metallic components, -Detection means for delivering magnetic resonance imaging (MRI) signals in cooperation with high-frequency means, -Means for processing MRI signals to provide characteristic information about the state of substantially metallic components.

[0030] According to the present invention, the components are exposed to a very weak magnetic field of less than 10 mT, and the detection means includes a pickup coil that is magnetically coupled with a polarization means and a high-frequency means and acts as a magnetic flux concentrator, and a SQUID (superconducting quantum interference device) detector positioned downstream of the pickup coil via a transformer.

[0031] In the following, “essentially metallic component” means any component or object that contains one or more metallic cores and / or whose physical composition is essentially metallic.

[0032] In a preferred embodiment of the present invention, the polarization means, the high-frequency means, and the pickup coil are enclosed within a shielded chamber.

[0033] It is advantageous that the SQUID detector and at least a portion of the processing means are housed within a cryostat.

[0034] The polarization means may include a gradient coil, and the pickup coil may have a volumetric glodometric geometry.

[0035] The pickup coil may have a surface geometry, particularly a quadratic gladometric surface geometry.

[0036] In a first application of the present invention, the pickup coil includes means for receiving an electrochemical cell, in particular a lithium-ion cell.

[0037] In a second application of the present invention, the pickup coil includes means for receiving an electronic chip or electronic component.

[0038] In a third application of the present invention, the pickup coil includes means for receiving an industrial machine structure.

[0039] In a fourth application of the present invention, the MRI imaging apparatus is adapted to image a power plant structure.

[0040] According to another aspect of the present invention, a method for magnetic resonance imaging of an object comprising at least one metal component is proposed, the method is - A step of generating a polarization magnetic field to be applied to object (a), - A step of exciting object (a) with radio frequency (RF) waves, - A step of detecting an MRI signal from the response of an object to high-frequency excitation, -The process includes the step of processing the MRI signal thus detected to provide information characteristic of the state of object (a).

[0041] According to the present invention, an object is exposed to a very weak magnetic field of less than 10 mT, and the detection step includes generating an inductive signal that is picked up by magnetic flux concentration in a pickup coil, and applying this picked-up signal to a SQUID detector.

[0042] The MRI imaging process according to the present invention can be advantageously carried out for characterization of an electrochemical cell and can be configured to provide a mapping of the electrochemical cell that represents the state of charge (SOC) and / or the state of health (SOH) of the electrochemical cell.

[0043] The MRI imaging method according to the present invention can be configured to provide a mapping of the electrochemical cell representing the state of health (SOH) of the electrochemical cell.

[0044] Therefore, the ultra-low field magnetic resonance imaging device for metal parts according to the present invention uses detection based on a low-temperature superconducting quantum interference device (SQUID). Using SQUID detection, it operates in magnetic fields ranging from 50 μT (the Earth's magnetic field) to several mT. By using an ultra-low magnetic field corresponding to a very low NMR frequency, it is possible to image metal samples, particularly electrochemical cells.

[0045] The MRI imaging device according to the present invention is designed for spatially resolved diagnosis of the state of metal parts, particularly the state of charge (SOC) and state of health (SOH) of electrochemical cells.

[0046] The MRI imaging method according to the present invention thus 7 can be used to characterize a lithium-ion cell containing a plurality of lithium nuclei including Li isotope nuclei. Then, it 7 includes the step of creating a spatially resolved image of the Li isotope nuclei and the step of estimating the density of the 7 Li nuclei within the spatially resolved image.

[0047] For 7 Li MRI imaging in this field of lithium-ion batteries, as prior art, the paper by Klamor et al.

[29] Klamor et al., " 7 In situ 1D NMR imaging of 7 a lithium ion battery)" Phys.Chem.Chem.Phys., 2015, 17, 4458 can be cited.

[0048] The imaging method according to the present invention 7The imaging method can be configured to provide a one-dimensional (1D) mapping of a lithium-ion cell, representing the state of charge (SOC) of the cell from an estimate of the Li nuclear density. In fact, this imaging method further involves using very high frequencies on the order of 500 MHz and does not enable 3D mapping due to the skin effect in conductors and susceptibility artifacts typical of high NMR frequencies. The method includes the steps of applying a voltage wave of a predetermined profile to the cell terminals while the lithium-ion cell is inserted into a pickup coil for imaging, simultaneously measuring the current entering the cell, and processing the current and voltage measurements to provide estimates of the cell's capacitance and state of charge.

[0049] To generate a map representing the state of health (SOH) of a lithium-ion cell housed in a pickup coil, the method may also provide the steps of: applying a voltage wave of a predetermined profile to the terminals of the cell until it reaches maximum charge; simultaneously measuring the current entering the cell; determining the effective maximum capacity of the cell; and estimating the state of health of the cell from the ratio between the thus determined effective maximum capacity and the initial maximum capacity of the cell.

[0050] The objective is to develop a low-cost, portable MRI device that can image metal samples in three dimensions (3D) without requiring careful operation. This is achieved by reducing the operating magnetic field from 1.5T, which is used in conventional medical devices, to less than 1mT. Since resistive magnets are used, the operating magnetic field can be easily set between 100μT and several mT.

[0051] The amount of available signal decreases linearly with magnetic field B0, which in this invention means at least 1000 times compared to high-field MRI. To counteract the signal loss, an ultra-sensitive antenna based on SQUID detection is used. A SQUID is a highly sensitive magnetometer made from a loop of superconducting material separated by two Josephson junctions. They have a very wide bandwidth and can detect DC signals up to 100 MHz with a flat frequency response. The superconductor needs to be cooled to a cryogenic temperature of 4K to operate, which is a problem for the heavy superconducting magnets used in conventional MRI. In the case of a SQUID, this is far less of a constraint, as it is mounted on a very small chip that is only a few centimeters in size and therefore requires only a very light cryogenic machine to operate.

[0052] SQUIDs are very small, generally being loops with a diameter of a few micrometers, and are often used in conjunction with antennas that act as flux concentrators. Such detectors, in the case of magnetic fields in the kHz range,

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[0053] (References) 1. Superconducting quantum interference device instruments and applications. RLFagaly et al., Review of Scientific Instruments 77 101101 (2006). 2. Electrochemical Impedance Spectroscopy: Principles, Construction, and Biosensing Applications. (EIS: Principles, Construction, and Biosensing Applications), HSMagar et all, Sensors (Basel) 19 6578 (2021). 3. SQUID-based magnetic resonance imaging at ultra-low magnetic fields using the backprojection method. (Q. Guo et all, Concepts in Magnetic Resonance part. B, Magnetic resonance engineering 8882329 (2020)). 4. Progress toward a deployable SQUID-based ultra-low field MRI system for anatomical imaging. MAEspy et all, IEEE transactions on applied super-conductivity, 25 no.3, 1601705 (2015). 5. MRI of the human brain at 130 microTesla. B. Inglis et all, PNAS 110 no.48, 19194-19201 (2013). 6. Real-time 3D imaging of microstructure growth in battery cells using indirect MRI.

[0054] AJIlott et all, PNAS113(39)10779-10784 (2016). 1. In-situ detection of charge state and defects in rechargeable lithium-ion batteries by inside-out magnetic resonance imaging. (AJIlott et all, Nature Communications 9 1776 (2018)). 2. Distortion-free inside-out imaging for rapid diagnostics of rechargeable lithium-ion cells.

[0055] K. Romanenko et all, PNAS 116(38)18783-18789(2019). 1. Diagnosing current distributions in batteries with magnetic resonance imaging. M. Mohammadi et al, J. Mag. Res. 309-106601 (2019). 2. Sensitive magnetometry reveals inhomogeneities in charge storage and weak transient internal currents in lithium-ion cells. (Y. Hu et all, PNAS 117(20) 10667-10672 (2020)). 3. Observation of memory effects associated with degradation of rechargeable lithium-ion cells using ultrafast surface-scan magnetic resonance imaging. (K. Romanenko et al, J. Mater. Chem. 21078-21084 (2021)). 4. S. Haber-Pohlmeier et al., Magnetic Resonance Microscopy: Instrumentation and Applications in Engineering, Life Science, and Energy Research, Chapters 17-18, Wiley-VCH, 2022. ISBN: 9783527827251. 5. Three-dimensional characterization of electrodeposited lithium microstructures using synchrotron X-ray phase contrast imaging. DSEastwood et all, Chem. Comunn. 51 266-268 (2015) 6. Three-dimensional high-resolution X-ray imaging and quantification of lithium-ion battery mesocarbon microbead anodes. F. Tariq et all, J. of Power Sources 248 1014-1020 (2014). 7. Characterization of the 3-dimensional microstructure of a graphite negative electrode from a lithium-ion battery. PRShearing et al, Electrochem.Comunn. 12-3, 374-377 (2010). 8. Microstructural investigations of commercially available lithium-ion battery electrodes at various length scales. (Multi-Length Scale Microstructural Investigations of a Commercially Available Li-Ion Battery Electrode), PRShearing et al, J. Electrochem. Soc. 159-7, 1023-1027 (2012). 9. Local Tortuosity Inhomogeneities in a Lithium Battery Composite Electrode. D. Kehrwald et all, J. Electrochem. Soc. 158-12-1393 (2011). 10. In-operando high-speed tomography of lithium-ion batteries during thermal runaway. DPFinegan et al, Nat.Comm.6 6924 (2015). 11. Non-invasive battery analysis via micro-computed tomography. ELBallard et al, U.S. Patent No. 7902518(B2) (2008). 12. In-situ battery diagnostic method using electrochemical impedance spectroscopy. R. Mingant et all, U.S. Patent No. 8849598(B2) (2010). 13. Method for determining the aging state of a battery cell by means of impedance spectroscopy, J. Ziegler et al, U.S. Patent Application Publication No. 20120019253(A1) (2009). 14. Methods and apparatus for battery testing. JATinnemeyer et all, U.S. Patent Application Publication No. 20110074432(A1) (2009). 15. Electrochemical impedance spectroscopy in battery management system, Chinese Patent Application Publication No. 107076801(A) (2015). 16. A kind of EIS method for fast measuring of lithium ion battery, Chinese Patent Application Publication No. 106970266(A) (2016). 17.https: / www.ieco.fi / index.php?k=10909 18.https: / www.shicryogenics.com / product / rp-082B2S-4K-pulse-tube-cryocooler-series / 19.https: / www.pure-devices.com / index.php / products / products-research / produits-recherche lecteurl.html 20. Moszle M et al: SQUID-detected microtesla MRI in the presence of metal, Journal of Magnetic Resonance, vol.179, No.1, March 1, 2006, pp. 146-151, XO024919553 21. Klamor et al.: "On site 7 NMR imaging of lithium-ion batteries in 1D using Li (Klamor et al: 7 "Li in situ 1D NMR imaging of a lithium ion battery)" Phys.Chem.Chem.Phys.,2015,17,4458 [Brief explanation of the drawing]

[0056] [Figure 1] This is a schematic diagram of a SQUID detection system implemented in an MRI imaging device according to the present invention. [Figure 2] This is an example of the geometric shape of a magnetic flux concentrator used in a SQUID detection system implemented in an MRI imaging device according to the present invention. [Figure 3] This is a schematic diagram of a metal component MRI imaging apparatus according to the present invention. [Modes for carrying out the invention]

[0057] Referring to Figure 1, the SQUID detection system 10 includes a magnetic flux concentrator 2 with an excitation coil c and a pickup coil b surrounding a metal component a such as a lithium-ion electrochemical cell, and an input inductor L iIt includes a shielded transformer 3 connected to the output and a SQUID 4 whose output signal is amplified by an LNA amplifier 5 ("low-noise amplifier") coupled to a phase-locked loop FLL 6 ("flux-locked loop") that controls the supply coil Lf.

[0058] SQUIDs can be fabricated from niobium, magnesium diboride (MgB), or any other medium-critical temperature superconducting material, or from high-temperature copper oxide.

[0059] The metal component is captured by pickup coil b, which acts as a magnetic flux concentrator, and input coil L is sent to SQUID4 via two terminals 20, 21, to which impedance matching capacitor Ca is connected in parallel. i It emits the signal transmitted through it. L1 and L2 shielded transformers are used for impedance matching and ground isolation.

[0060] Excitation coil c is connected to MRI console d. The SQUID signal output is amplified via low-noise amplifier LNA5, while operational stability is ensured by flux-locked loop FLL6.

[0061] In this example, the pickup coil is a saddle coil, but a glidometer antenna, as illustrated in Figure 2, is often preferred.

[0062] In most SQUID MRI experiments, the pickup coil is a secondary surface gradiometer, as described in Fagaly et al.[1].

[0063] In this invention, it is preferable to use a volumetric geometry that captures more signals while maintaining robustness against noise. To maintain a gradiometric configuration and robustness against noise from distant sources, the antenna consists of two saddle coils wired in series with opposite currents. This particular geometry was the subject of a patent application filed on April 12, 2022, under the name of the same applicant.

[0064] The pickup coil 2' has a first saddle coil c' surrounding a second saddle coil b'. The first coil c' includes a first longitudinal conductor c1, a first end conductor c2, a second longitudinal conductor c3, a second end conductor c4, a third longitudinal conductor c5, a third end conductor c6, and a fourth longitudinal conductor c7 connected to the first output conductor 21 to the transformer 3.

[0065] The second coil b', concentric with the first coil c', includes a first longitudinal conductor b1, a first end conductor b2, a second longitudinal conductor b3, a second end conductor b4, a third longitudinal conductor b5, a third end conductor b6, and a fourth longitudinal conductor b7 connected to the second output conductor 20 to the transformer 3.

[0066] Referring to Figure 3, an MRI imaging device 1 for metal components such as lithium-ion electrochemical cells will be described.

[0067] The MRI imaging apparatus 1 according to the present invention includes a magnetic flux concentrator 2'' configured to accept a metal component a, such as a chemical cell. A coil b generates a magnetic field B0 that polarizes the target atomic nuclei in the metal component a, and generates energy levels separated by energy hω0.

[0068] The flux concentrator 2" also includes a gradient coil h used to generate spatial resolution in the MRI image. This coil h is supplied via a pair of conductors 8c by a stabilized current source c that provides a very regular current on the order of several amperes to tens of amperes, depending on the exact shape of the coil.

[0069] The gradient coil b'' is fed by a gradient amplifier d, for example, a model XPA-175-350 from IECO of Finland

[25] . To keep the magnetic field very stable and uniform within the field of view, the magnetic field is continuously monitored by a fluxgate magnetometer probe e. Low-frequency fluctuations of the magnetic field are measured and commands are sent in real time to a current source to maintain the magnetic field fluctuations within a typical drift of 50 ppm over the duration of the MRI acquisition.

[0070] The high-frequency amplifier f supplies power to a high-frequency coil g, which may have, for example, a birdcage-type configuration, to transmit a pulse B1 tuned to the magnetic resonance frequency ω0. The signal is then picked up by the detection system shown in Figure 2.

[0071] The pickup coil h transmits the signal to the SQUID and the rest of the read chain i inside a 4K cryostat j, which is cooled by a cryogenic refrigerator k, such as Sumitomo's RP-082B2S

[26] .

[0072] The output signal is then processed at room temperature by an analog-to-digital conversion module and an MRI console 1, for example, a drive-1 model from Pure Devices

[27] , which interprets the time signal as an MRI image displayed on a screen m. The polarization system, excitation coils and detection coils, and metal components a are all enclosed within a shielded chamber n consisting of a metal grid acting as a Faraday cage, layers of magnetic material such as ferrite or mu-metal to protect the system from shielding signals in the range of 10 kHz or higher, and very low frequency noise below a few kHz.

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[0073] The ultra-low field MRI processes described herein are particularly suitable for direct MRI imaging of a single lithium-ion cell or cell assembly. Compared to the MRIio techniques described above, the direct MRI processes provide images of the cell interior with contrast that show local SOC and SOH time-resolved maps. Several possible strategies exist here. - Li MRI sequences to map the local lithiumization state of the cathode and provide spatially resolved insights into the local SOC charge state [7] - 3C MRI sequencing for studying SOC in the anode;[1] Susceptibility-weighted MRI sequences can provide access to a spatially resolved map of susceptibility linked to local SOC and SOH, as shown by Illot et al.[5].

[0074] The following are approximate quantitative estimates of key device parameters. - While the acquisition time for a fully resolved image is approximately 5 minutes, faster sequences with less information can be performed in a few seconds. - Spatial resolution in the millimeter range, most likely on the order of 1.0-2.5 mm in-plane resolution. - Up to 50cm, and potentially even larger, object volumes (field of view). This makes it possible to image a single cell or a collection of cells in a single acquisition. - A portable device with wheels, the size of a small washing machine, weighing approximately 100 kg.

[0075] Possible uses - Evaluation of the State of Charge (SOC) and State of Health (SOH) of an electrochemical cell or full battery composed of a cell assembly by providing spatially decomposed maps of the State of Charge (SOC) and State of Health (SOH) during operation. - Quality control of electrochemical cells. - Quality control and monitoring of electronic chips and electronic components. - Detection of defects in metal structures in the following industries: automotive, construction, energy, defense and aerospace, and transportation infrastructure. - Medical MRI of patients with metal implants.

[0076] Naturally, the present invention is not limited to the embodiments described above, and numerous other embodiments can be envisioned without departing from the scope of the present invention.

Claims

1. A magnetic resonance imaging (MRI) apparatus (1) configured to perform imaging of substantially metallic components, - Means (b'') for generating a polarization magnetic field intended to be applied to the essentially metallic component (a), - A high-frequency means (g) for exciting the essentially metallic component (a), - A detection means (10) for delivering magnetic resonance imaging (MRI) signals in cooperation with the aforementioned high-frequency means (g), Means (1) for processing the MRI signal to provide information characteristic of the state of the essentially metallic component (a), Equipped with, A magnetic resonance imaging (MRI) apparatus (1) characterized in that the essentially metallic component (a) is exposed to a very weak magnetic field of less than 10 mT, and the detection means (10) comprises a pickup coil (h) which is magnetically coupled with the polarization means (b'') and the high-frequency means (g) and acts as a magnetic flux concentrator, and a SQUID (superconducting quantum interference device) detector (4) which is located downstream of the pickup coil (h) via a transformer (3).

2. The MRI imaging apparatus (1) according to claim 1, characterized in that the polarization means (b''), the high-frequency means (g), and the pickup coil (h) are enclosed in a shielded chamber (n).

3. The MRI imaging apparatus (1) according to claim 2, characterized in that at least a portion of the SQUID detector (4) and the processing means (i) are arranged within a cryostat (j).

4. The MRI imaging apparatus (1) according to claim 1, characterized in that the polarization means (b") includes a gradient coil.

5. The MRI imaging apparatus according to claim 1, characterized in that the pickup coil (2') has a volumetric gliometric geometric shape.

6. The MRI imaging apparatus according to claim 1, characterized in that the pickup coil has a surface geometric shape, particularly a secondary gladometric surface geometric shape.

7. The MRI imaging apparatus according to claim 1, characterized in that the pickup coil (h) includes means for receiving an electrochemical cell (a), particularly a lithium-ion cell.

8. The MRI imaging apparatus according to claim 1, characterized in that the pickup coil includes means for receiving an electronic chip or electronic component.

9. The MRI imaging apparatus according to claim 1, characterized in that the pickup coil includes means for receiving an industrial machine structure.

10. The MRI imaging apparatus according to claim 1, characterized in that it is adapted for imaging the structure of a power plant.

11. A method for magnetic resonance imaging of an essentially metallic component body (a) including at least one metallic portion, which is implemented in the imaging apparatus according to claim 1, - A step of generating a polarization magnetic field intended to be applied to the metal component (a), - The step of exciting the essentially metallic component (a) with a high-frequency (RF) wave, - A step of detecting an MRI signal of the response of the essentially metallic component to high-frequency excitation, - A step of processing the MRI signal thus detected to provide characteristic information relating to the state of the essentially metallic component (a), Includes, The method is characterized in that the essentially metallic component is exposed to a very weak magnetic field of less than 10 mT, and the detection step includes generating an inductive signal that is picked up by magnetic flux concentration in a pickup coil (h), and applying this picked-up signal to a SQUID detector (4).

12. The MRI imaging method according to claim 11, which is implemented to characterize an electrochemical cell (a).

13. ７ An MRI imaging method implemented to characterize a lithium-ion cell containing multiple lithium nuclei, including Li isotope nuclei, wherein ７ A step of creating a spatially resolved image of Li isotope nuclei, and in the spatially resolved image ７ The MRI imaging method according to claim 12, characterized by comprising the step of estimating the density of Li nuclei.

14. The aforementioned ７ MRI imaging method according to claim 13, configured to provide a mapping of the lithium-ion cell representing the state of charge (SOC) of the cell from an estimated Li nuclear density, further comprising the steps of: applying a voltage wave of a predetermined profile to the terminals of the cell while the lithium-ion cell is inserted into the pickup coil for imaging; simultaneously measuring the current entering the cell; and processing the current measurement and voltage measurement to provide an estimate of the capacity and state of charge of the lithium-ion cell.

15. The aforementioned ７ MRI imaging method according to claim 13 or 14, configured to provide a mapping of the lithium-ion cell representing the state of health (SOH) of the cell from an estimated Li nuclear density, further comprising: applying a voltage wave of a predetermined profile to the terminals of the electrochemical cell until it reaches a maximum charge while the cell is inserted into the pickup coil for imaging; simultaneously measuring the current entering the electrochemical cell; determining the effective maximum capacity of the electrochemical cell; and estimating the state of health of the cell from the ratio between the effective maximum capacity thus determined and the initial maximum capacity of the lithium-ion cell.

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