Apparatus and method for performing magnetic resonance imaging of metallic or partially metallic components and application of said method to imaging of 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 encompasses 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 the spin of an electron or an atomic nucleus. In the case of medical NMR, the nucleus of interest is most often water, fat, or hydrogen (which has only one proton) present in human body tissues.

[0003] An NMR (or MRI) experiment is performed in several precise steps. First, the sample (in imaging of a lithium-ion cell or any metallic part, this is the part itself) is placed in a very uniform static magnetic field, B, called the polarizing field, which is generated by a large superconducting coil. In most commercial instruments, this field varies from 1.5 T to over 10 T. As the sample protons are placed in the magnetic field B, they lead around this field at a frequency ω given by ω = γ, where γ is called the gyromagnetic ratio.

[0004] The protons are then excited by a radio frequency signal with the same frequency as the proton precession, ω = ω. This excitation displaces the protons from their precession, and after a while, they slowly decay back to their original precession state, emitting a signal that is detected by an antenna. Measuring this signal is the means by which information about the composition of the body's interior can be gathered and ultimately used to reconstruct an MRI image.

[0005] The overall principle of the MRI experiment can be summarized as follows. The part of the body to be imaged is placed in a static uniform magnetic field B0. -When placed in this magnetic field, the protons will lead with frequency ω0 = γB0. The excitation antenna is used to transmit pulses of intensity B1 and frequency ω=ω0 tuned to the precession of the protons. - The protons are sent to a higher energy state, sending a signal of intensity B2 and frequency ω0, which decays back to their original state. More importantly, this signal decays with 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 characteristic of the exact state at each point in the sample and are used to generate contrast in MRI images. In the case of 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 where the signals detected by the MRI antenna come from. For this purpose, gradient coils are used. In addition to the permanent, uniform magnetic field B0, they add a small auxiliary magnetic field δB(x,y,z) that varies linearly along the three directions in space.

[0007] Typically, in an MRI machine with a magnetic field of 5 T, the -1 An additional magnetic field δB of the order of magnitude is observed. Since the resonant frequency of the nuclei is proportional to the local magnetic field, gradient fields can be used to spatially encode the resonant frequency and phase of the signal, thereby forming a 3D image.

[0008] During an MRI sequence, these gradient fields are rapidly varied on a millisecond time scale to selectively excite specific portions of the sample. The models chosen to apply the gradients and excitation pulses constitute an MRI sequence.

[0009] Different sequences allow different contrasts to be displayed, allowing different things to be seen. In medical MRI, a wide variety of sequences exist, some adapted to see blood vessels (time-of-flight sequences), others more suited to functional imaging (BOLD, which stands for "blood oxygenation level dependent"), and the more common T1 or T2 weighted sequences, which can distinguish between fat, organic tissue, tumors, etc.

[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] We next explain why it is necessary to use low-field MRI to image metallic samples.

[0012] For over 40 years, MRI innovation has consistently moved toward higher magnetic fields. Higher field strength means that more nuclei in the sample are polarized, resulting in a higher signal-to-noise ratio. Furthermore, because the detection frequency is proportional to the magnetic field, it allows typical inductive detection antennas to operate at higher frequencies, a range in which they are inherently more sensitive. In essence, higher field strength means better resolution and shorter acquisition times. However, this strategy has clear drawbacks. Commercial high-field machines require heavy, expensive superconducting magnets cooled to 4 Kelvin with liquid helium, necessitating 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 dedicated, magnetically shielded rooms with reinforced floors. This makes MRI a more extensive imaging procedure than ultrasound or CT.

[0013] A less obvious problem with high-field MRI is that it is not possible to image in the presence of metals, let alone image metallic samples. - Having a sample with both metallic and non-metallic parts means that there are large local differences in magnetic susceptibility, which causes field gradient artifacts that disrupt the linearity of the gradient field patterns 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 a conductor / dielectric interface, eddy currents are generated within the inductor. These eddy currents then generate another magnetic field that compensates for the emerging magnetic field. As a result, the total magnetic field effectively vanishes once it has entered the bulk of the conductive sample. The penetration depth δ is a measure of the depth to which a magnetic field can penetrate inside a metallic sample.

number

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

[0016] For proton MRI, γ H / (2π):42MHz.T -1 whereas for lithium, this number is γ Li / (2π):16.5MHz.T -1 In either case, this means that in conventional high-field MRI, excitation frequencies used are 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 metallic samples impossible. The following table summarizes typical resistivities and penetration depths associated with typical metals used in lithium-ion cell compositions or packaging: [Table 1]

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

[0018] Therefore, to operate at lower frequencies, the magnetic field needs to be reduced. This also means lighter, lower-cost machines that do not require extensive maintenance or magnetic shielding and are not susceptible to magnetic susceptibility artifacts. However, simply reducing the field with conventional machines results in a much lower SNR (signal-to-noise ratio), which means poorer image quality and longer acquisition times.

[0019] One possible solution is the use of SQUIDs (for "superconducting quantum interference device"), which are ultrasensitive magnetometers that allow the magnetic field of an NMR experiment to be reduced while maintaining a sufficient signal-to-noise ratio (SNR) to produce images with good resolution and contrast in a reasonable time. Using this technique, MRI images can be produced in magnetic fields ranging from 100 μT to several mT. Based on lithium, this implies NMR frequencies ranging from 1.6 kHz to approximately 20 kHz. Looking at the table, this implies a penetration depth ranging from a few mm to 1 cm, depending on the metal, making it possible to image metallic samples.

[0020] One example is the work of Alexej Jerschow and his team at New York University. To circumvent the problems associated with high frequencies and the skin effect, the team devised a technique called inverted MRI (ioMRI, for "IntraOperative Magnetic Resonance Imaging") [6][7]. This technique is described in detail in a very recent book by Haber-Pohlmeier, Bliimich, and Ciobanu

[12] . The idea is not to create a direct image of the lithium-ion cell, but to use MRI of the cell's surrounding environment to perform an indirect measurement of the local magnetic susceptibility of the anode and cathode. More precisely, the cell is placed in a holder containing a measurement medium, usually doped water, that surrounds the lithium-ion cell. A permanent magnetic field B is then applied to the cell. The cell then generates a secondary magnetic field B, proportional to the local magnetic susceptibility of the cell components, and this secondary field is mapped with a special MRI sequence of the surrounding doped water. For a schematic 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 susceptibility of the anode and cathode. This overall magnetic susceptibility is then related to the SOC (State of Charge) as shown in Figure 2 by Ilott et al. 2018 [7]. The figure shows the measured overall magnetic susceptibility as a function of the SOC.

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

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

[0024] To date, SQUID MRI has not seen any breakthroughs due to the lack of SNR available at low magnetic fields. To increase the SNR, most attempts have used a technique called pre-polarization. First, a high pulsed field of approximately 100 mT is applied to increase the Boltzmann polarization of the sample, which increases linearly with the magnetic field. The magnetic field is then rapidly decreased, and MRI acquisition is performed at a target magnetic field, typically around 100 μT.

[0025] This allows for both moderately high polarization at 100 mT and the benefits associated with ultra-low fields, primarily improved contrast and reduced field homogeneity constraints. However, pre-polarization requires heavy machinery to generate the pulsed field and complex shielding to counteract noise caused by eddy currents. More importantly, the rapid switching of the magnetic field makes this technique impractical for 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 involving SQUID detection of organic components in the presence of metal. Using this method, the authors were able to image organic samples, in this case bell peppers, encased in a 200 μm thick aluminum case or surrounded by 20 μm thick aluminum foil, see page 149. Summary of the Invention

[0027] However, state-of-the-art imaging equipment is unable to perform magnetic resonance imaging of metal parts with sufficient image quality for industrial use.

[0028] OBJECTS AND SUMMARY OF THE INVENTION The object of the present invention is precisely to remedy the above limitations by providing an apparatus for MRI imaging of metal parts, which is able to provide spatially resolved mapping thereof.

[0029] DISCLOSURE OF THE INVENTION This object is achieved by a magnetic resonance imaging (MRI) device configured to perform imaging of a substantially metallic component, the device comprising: means for generating a polarizing magnetic field intended to be applied to the substantially metallic component; - high frequency means for exciting the substantially metallic component; - detection means for cooperating with the radio frequency means to deliver magnetic resonance imaging (MRI) signals; - means for processing the MRI signals to provide characteristic information regarding the condition of the substantially metallic component.

[0030] According to the invention, the component is exposed to a very weak magnetic field of less than 10 mT, and the detection means comprises a pick-up coil magnetically coupled to the polarizing means and radio frequency means and acting as a magnetic flux concentrator, and a SQUID (Superconducting Quantum Interference Device) detector located downstream of the pick-up 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 polarising means, radio frequency means and pick-up coil are enclosed within a shielded chamber.

[0033] Advantageously, the SQUID detector and at least part of the processing means are housed within a cryostat.

[0034] The polarising means may include gradient coils and the pick-up coil may have a volume gradiometric geometry.

[0035] The pickup coil may have a surface geometry, in particular a quadratic gradiometric surface geometry.

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

[0037] In a second application of the invention, the pickup coil comprises 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 device is adapted to image a power plant structure.

[0040] According to another aspect of the invention, a method for magnetic resonance imaging of an object comprising at least one metal part is proposed, the method comprising the steps of: - generating a polarizing magnetic field that is applied to the object (a); - exciting an object (a) with radio frequency (RF) waves; - detecting an MRI signal from the object's response to the radio frequency excitation; - processing the MRI signals thus detected so as to provide information characteristic of the state of the object (a).

[0041] According to the present invention, the object is exposed to a very weak magnetic field of less than 10 mT, and the detection step includes generating an induced signal that is picked up by a 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 performed for the characterization of an electrochemical cell and can be configured to provide a mapping of the electrochemical cell indicative of the state of charge (SOC) of the electrochemical cell and / or indicative of its state of health (SOH).

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

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

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

[0046] The MRI imaging method according to the invention therefore comprises: 7 It can be used to characterize lithium-ion cells containing multiple lithium nuclei, including Li isotope nuclei. 7 generating a spatially resolved image of Li isotope nuclei; 7 and estimating the density of Li nuclei.

[0047] Lithium-ion battery 7 In this area of ​​Li MRI imaging, the prior art is the paper by Klamor et al.

[29] Klamor et al., “Lithium-ion Battery 7 In situ 1D NMR imaging of Li ( 7 Li in situ 1D NMR imaging of a lithium ion battery,” Phys. Chem. Chem. Phys., 2015, 17, 4458.

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

[0049] To generate a map representing the state of health (SOH) of a lithium-ion cell contained within the pickup coil, the steps of applying a voltage wave of a predetermined profile to the terminals of the cell until a maximum charge is reached, 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 effective maximum capacity thus determined and the initial maximum capacity of the cell may also be provided.

[0050] The goal is to develop a low-cost, portable MRI machine that requires no care in operation and can image metal samples in three dimensions (3D). This is achieved by reducing the operating magnetic field from the 1.5 T used in conventional medical machines to less than 1 mT. Because resistive magnets are used, the working field can be easily set between 100 μT and a few mT.

[0051] The amount of available signal decreases linearly with the magnetic field B0, which means at least 1000 times greater in our case compared to high-field MRI. To counteract this signal loss, we use an ultrasensitive antenna based on SQUID detection. SQUIDs are highly sensitive magnetometers made from a loop of superconducting material interrupted by two Josephson junctions. They have a very wide bandwidth and can detect DC signals of 100 MHz with a flat frequency response. Superconductors must be cryogenically cooled to 4 K to operate, which is a problem for the heavy superconducting magnets used in conventional MRI. This is much less of a constraint for SQUIDs, which are mounted on a very small chip, only a few centimeters in size, and therefore require only very light cryogenic machinery to operate.

[0052] Because SQUIDs are very small, typically loops with a diameter of a few microns, they are often used in conjunction with antennas that act as flux concentrators. For magnetic fields in the kHz range, such detectors are

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[0053] (References) 1. Superconducting quantum interference device instruments and applications, R.L. Fagaly et al., Review of Scientific Instruments 77 101101 (2006). 2. Electrochemical Impedance Spectroscopy: Principles, Construction, and Biosensing Applications. (Electrochemical Impedance Spectroscopy, EIS: Principles, Construction, and Biosensing Applications), HSMagar et al., Sensors (Basel) 19 6578 (2021). 3. SQUID-Based Magnetic Resonance Imaging at Ultra-Low Field Using the Backprojection Method. (SQUID-Based Magnetic Resonance Imaging at Ultra-Low Field Using the Backprojection Method) Q. Guo et al., 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 al., IEEE transactions on applied superconductivity, 25 no. 3, 1601705 (2015). 5. MRI of the human brain at 130 microtesla. B. Inglis et al., 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. Rechargeable lithium-ion cell State of charge and defect detection by in-situ inside-out magnetic resonance imaging, AJ Ilott et al., Nature Communications 9 1776 (2018). 2. Distortion-free inside-out imaging for rapid diagnostics of rechargeable Li-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 Li-ion cells, Y. Hu et al., 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. D.S. Eastwood et al., 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 al., J. of Power Sources 248 1014-1020 (2014). 7. Characterization of the 3-dimensional microstructure of a graphite negative electrode from a Li-ion battery, P.R. Shearing et al., Eletrochem. Comunn. 12-3, 374-377 (2010). 8. Multi Length Scale Microstructural Investigations of a Commercially Available Li-Ion Battery Electrode, P.R. Shearing et al., J. Electrochem. Soc. 159-7, 1023-1027 (2012). 9. Local Tortuosity Inhomogeneities in a Lithium Battery Composite Electrode, D. Kehrwald et al., J. Electrochem. Soc. 158-12-1393 (2011). 10. In-operando high-speed tomography of lithium-ion batteries during thermal runaway, D.P. Finegan et al., Nat. Comm. 6 6924 (2015). 11. Non-invasive battery analysis via micro-computed tomography, E.L. Ballard et al., U.S. Patent No. 7,902,518 (B2) (2008). 12. In-situ battery diagnosis method using electrochemical impedance spectroscopy, R. Mingant et al., U.S. Patent No. 8,849,598 (B2) (2010). 13. Method for determining an aging condition 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, J.A. Tinnemeyer et al., U.S. Patent Application Publication No. 20110074432(A1) (2009). 15. Electrochemical impedance spectroscopy in battery management system, China Patent Application Publication No. 107076801(A) (2015). 16. A kind of EIS method for fast measuring of lithium ion battery, China 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.: “In the field 7 1D NMR imaging of lithium-ion batteries 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 drawings]

[0056] [Figure 1] 1 is a schematic diagram of a SQUID detection system implemented in an MRI imaging apparatus according to the present invention; [Figure 2] 1 is an example of a flux concentrator geometry for use in a SQUID detection system implemented in an MRI imaging device according to the present invention. [Figure 3] 1 is a schematic diagram of a metal part MRI imaging device according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0057] Referring to FIG. 1, a SQUID detection system 10 includes a magnetic flux concentrator 2 including 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 iand a SQUID 4 whose output signal is amplified by an LNA amplifier 5 (short for "low noise amplifier") coupled to a phase-locked loop FLL 6 (short for "flux-locked loop") which controls a supply coil Lf.

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

[0059] The metallic part is picked up by a pickup coil b, which acts as a magnetic flux concentrator, and the SQUID 4 is connected to the input coil L via two terminals 20 and 21 connected in parallel with an impedance matching capacitor Ca. i The signal transmitted through the L1 and L2 shield transformers is used for impedance matching and ground isolation.

[0060] The excitation coil c is connected to an MRI console d. The SQUID signal output is amplified through a low noise amplifier LNA 5, while operational stability is ensured by a flux locked loop FLL 6.

[0061] In this example, the pickup coil is a saddle coil, although a gradiometer antenna such as that shown in FIG. 2 is often preferred.

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

[0063] The present invention preferably uses a volumetric geometry that captures more signal while remaining robust to noise. To maintain the gradiometric configuration and remain robust to noise from distant sources, the antenna consists of two saddle coils wired in series with opposing currents. This particular geometry was the subject of a patent application filed April 12, 2022 in the name of the same applicant.

[0064] The pickup coil 2' has a first saddle-shaped coil c' surrounding a second saddle-shaped 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] With reference to FIG. 3, an MRI imaging device 1 for metal components such as lithium-ion electrochemical cells is described.

[0067] The MRI imaging apparatus 1 according to the present invention comprises a magnetic flux concentrator 2'' configured to receive a metal part a, such as, for example, a chemical cell. A coil b generates a magnetic field B0 that polarizes the nuclei of interest in the metal part a, generating energy levels separated by an energy hω0.

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

[0069] The gradient coils b” are powered by gradient amplifiers d, e.g., model XPA-175-350 from IECO, Finland

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

[0070] A radio frequency amplifier f feeds a radio frequency coil g, which may have, for example, a birdcage shape, to transmit pulses B1 tuned to the magnetic resonance frequency ω0. The signal is then picked up by the detection system described in FIG.

[0071] The pickup coil h transmits the signal to the SQUID and the rest of the readout chain i inside a 4 K cryostat j cooled by a cryocooler k, e.g., a Sumitomo 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 the 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 and detection coils and metal parts a are all enclosed in a shielded chamber n consisting of a metal grid acting as a Faraday cage, shielding signals in the range of 10 kHz and above, and a layer of magnetic material such as ferrite or mu metal that protects the system from very low frequency noise below a few kHz.

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[0073] The ultra-low field MRI process described herein is particularly suited for direct MRI imaging of single lithium-ion cells or cell assemblies. Compared to the MRI techniques described above, the direct MRI process provides images of the interior of the cell with contrast that reveals time-resolved maps of the local SOC and SOH. Here, several possible strategies exist. - Li MRI sequence to map the local lithiation state of the cathode and provide spatially resolved insight into the local SOC state of charge [7] -3C MRI sequence to study SOC at the anode; [1] Susceptibility-weighted MRI sequences can provide access to spatially resolved maps of magnetic susceptibility that are linked to regional SOC and SOH, as shown by Illot et al. [5].

[0074] Below are approximate quantitative estimates of important device parameters. -Acquisition time is about 5 minutes for a fully resolved image, but fast sequences with less information can be performed in a few seconds. -Spatial resolution in the millimeter range, most likely in-plane resolution on the order of 1.0-2.5 mm. - Volume of interest (field of view) of up to 50cm, and in some cases even larger, which allows imaging of single cells or cell clusters in a single acquisition. -Portable device on 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 cell assemblies by providing spatially resolved maps of SOC and 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, transport infrastructure. - Medical MRI of patients with metal implants.

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

Claims

1. A magnetic resonance imaging (MRI) device (1) configured to perform imaging of a substantially metallic component, comprising: - means (b") for generating a polarizing magnetic field intended to be applied to said essentially metallic component (a); - high frequency means (g) for exciting said essentially metallic component (a); - detection means (10) for delivering magnetic resonance imaging (MRI) signals in cooperation with said radio frequency means (g); means (1) for processing said MRI signals to provide information characteristic of the condition of said essentially metallic component (a); Equipped with 1. A magnetic resonance imaging (MRI) apparatus (1), characterized in that the essentially metallic component (a) is subjected to a very weak magnetic field of less than 10 mT, and the detection means (10) comprises a pickup coil (h) magnetically coupled to the polarization means (b") and radio frequency means (g) and acting as a magnetic flux concentrator, and a SQUID (Superconducting Quantum Interference Device) detector (4) arranged downstream of the pickup coil (h) via a transformer (3).

2. MRI imaging device (1) according to claim 1, characterized in that said polarising means (b"), said radio frequency means (g) and said pick-up coil (h) are enclosed in a shielded chamber (n).

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

4. MRI imaging device (1) according to any one of claims 1 to 3, characterized in that the polarising means (b") comprise gradient coils.

5. MRI imaging device according to any one of claims 1 to 4, characterized in that the pickup coil (2') has a volume gradiometric geometry.

6. MRI imaging device according to any one of claims 1 to 5, characterized in that the pickup coil has a surface geometry, in particular a quadratic gradiometric surface geometry.

7. MRI imaging device according to any one of claims 1 to 6, characterized in that the pickup coil (h) comprises means for receiving an electrochemical cell (a), in particular a lithium-ion cell.

8. MRI imaging apparatus according to any one of claims 1 to 7, characterized in that the pickup coil includes means for receiving an electronic chip or component.

9. MRI imaging device according to any one of claims 1 to 8, characterized in that the pickup coil includes means for receiving an industrial mechanical structure.

10. MRI imaging device according to any one of claims 1 to 9, characterized in that it is adapted to image power plant structures.

11. A method for magnetic resonance imaging of an essentially metallic component body (a) comprising at least one metallic part, implemented in an imaging device according to any one of claims 1 to 10, comprising the steps of: - generating a polarizing magnetic field intended to be applied to said essentially metallic component (a); - exciting said essentially metallic component (a) with radio frequency (RF) waves; - detecting an MRI signal of the response of said essentially metallic component to a radio frequency excitation; - processing said MRI signals thus detected so as to provide characteristic information regarding the state of said essentially metallic component (a); Including, The method is characterized in that the essentially metallic component is subjected to a very weak magnetic field of less than 10 mT, and the detecting step comprises generating an induced signal that is picked up by a magnetic flux concentration in a pick-up coil (h) and applying this picked-up signal to a SQUID detector (4).

12. 12. The MRI imaging method of claim 11 implemented for characterizing an electrochemical cell (a).

13. ７ 1. An MRI imaging method implemented to characterize a lithium ion cell containing a plurality of lithium nuclei, including Li isotope nuclei, comprising: ７ generating a spatially resolved image of Li isotope nuclei; ７ 13. The MRI imaging method of claim 12, further comprising the step of: estimating the density of Li nuclei.

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

15. The aforementioned ７ 15. The MRI imaging method of claim 13 or 14, configured to provide a mapping of the lithium-ion cell indicative of the state of health (SOH) of the cell from Li nuclei density estimates, further comprising the steps of applying a voltage wave of a predetermined profile to the terminals of the electrochemical cell until a maximum charge is reached while the cell is inserted in the pickup coil for imaging, simultaneously measuring the current entering the electrochemical cell, determining a maximum usable capacity of the electrochemical cell, and estimating the state of health of the cell from the ratio between the determined maximum usable capacity and the initial maximum capacity of the lithium-ion cell.

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