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Diffuse idiopathic skeletal hyperostosis (DISH) is a noninflammatory progressive disease resulting in ossification of the anterior longitudinal ligament of the spine and tendons. Herein, we describe a case of DISH in a patient on long-term hemodialysis. The patient was a 79-year-old man undergoing hemodialysis for chronic kidney disease due to diabetic nephropathy. He presented to the emergency department complaining of back pain after a slip and fall. Radiographs revealed bamboo spine-like findings, extending from the cervical to the lumbar spine. Computed tomography and magnetic resonance imaging revealed a compression fracture of thoracic vertebra 12, with abnormal ossification of the anterior longitudinal ligament. Inter-vertebral vertical osseous bridges were also observed at the cervical 7 and lumbar 2 vertebrae. There was no obvious spinal cord compression. Leukocytosis and C-reactive protein levels were not elevated and the human leukocyte type antigen HLA-B27 test was negative. Based on this finding, a diagnosis of DISH was made. In the absence of neurological findings, the patient was treated conservatively. Our findings show an overlap between the clinical features of DISH and those of hemodialysis patients, including older age, male sex, and diabetes.

The aim of this study is to observe the spatial inhomogeneity of a rechargeable battery's electric conductivity distribution. Therefore, we have developed a system that uses the measurement results of a minute magnetic field that leaks from the cell to visualize, in real time, the cell's electric conductivity distribution. This system has a magnetic detection capability of 30 pT/Hz(0.5) (at 1 Hz); it measures the magnetic field distribution in the 240 x 240-mm range. This system has the ability to detect the 500-µA electric current that flows in a rechargeable battery 5 mm away from the sensor module. Because the magnetic signals are detected at the frequency synchronized with the alternating current flowing in the cell, this system is not affected by environmental magnetic field noise. Using this system, we have successfully visualized the short-circuit spot in a cell with significant self-discharge. Furthermore, we observe that the magnetic field distribution changes continually when the short circuit is being generated. The coordinate where the magnetic field distribution changed and the coordinate where metal precipitates were confirmed significant agreement.

The sentinel lymph node is the first lymph-node-draining cancer metastasis. The identification of the sentinel lymph node using magnetic particles and a magnetic sensor has attracted attention in recent years, as this method is less invasive than the conventional method of radiotracer injection. However, the development of a two-dimensional measurement method for sentinel lymph nodes using magnetic nanoparticles remains an issue. In the present study, a method and apparatus for the two-dimensional imaging of magnetic particle distribution were developed to detect a lymph node with magnetic particles concentrated within lymphoid tissues. The method comprises the reconstruction of the magnetic field measured with a high-sensitivity magnetic sensor and with a magnetic detection ability of 2 nT/√Hz at 100 Hz (5 nT/√Hz at 1 Hz). The proposed system measures the two-dimensional magnetic field distribution in an area of up to 25 × 25 mm2 using a coil generating a 0.77 mT external magnetic field applied to the measurement target. The improved spatial resolution of the images makes it possible to use two-dimensional imaging for diagnostics of breast cancer metastases.

Recently, miniaturization and three-dimensional integration for improving the performance of electric devices have been accelerated, and smaller storage batteries with higher energy density and shrinked electric components have been more required. Therefore, failure analysis technologies targeted for these cutting-edged devices should be developed for increasing production yields and reducing product accidents. In mass production processes, pre-shipment inspections are performed on the core parts of electronic devices. In the case of electronic parts, energization check is adopted, and in the case of storage batteries, voltage drop, that is called to be an aging test, is checked. However, many cases have been reported in which products, that have passed the inspection, cause accidents. One of the typical causes of failures related about electronic components is internal electric-short caused by foreign matters mixed into the insulation or whiskers accidentally generated from the electrodes and wiring. Similarly, storage batteries also accidentally have internal short circuits due to foreign matter contaminations and dendrite formation at the electrodes. The internal short-circuited points of electronic components and storage batteries are identified by X-ray imaging method. However, it is difficult to acquire the contrast due to the lack of the dynamic range required for visualization of short-circuited parts because the wirings and insulation areas between electrodes have been significantly miniaturized. In addition, short circuits between wirings on the surface of electronic circuit boards have been visualized by thermography, although it is difficult to apply electronic components with multi-layered electrodes. Then we have focused on the relationship between the electric current distribution inside the devices and the magnetic field generated from it and spread toward outside, we have succeeded in deriving the analysis solution of the inverse problem for the first time. Combining this novel theory and a highly-sensitive magnetic field detection based on quantum effect, we have developed a subsurface electric current imaging system capable of detecting electric short-circuited points in the deep region. In this study, we discuss about the details of the theory about the analytical solution of the inverse problem and the visualization system, and show some results of failure analysis for actual electronic components and storage batteries. [1] Yuki Mima, Noriaki Oyabu, Takeshi Inao, Noriaki Kimura, Kenjiro Kimura, “Failure analysis of electric circuit board by high resolution magnetic field microscopy” Proceedings of IEEE CPMT Symposium Japan, pp.257-260, 2013. [2] Kenjiro Kimura, Yuki Mima, Noriaki Kimura, “Local electric current reconstruction theory for nondestructive inspection inside battery cell using magnetic field measurement”, Subsurface Imaging Science & Technology, 1, 1, pp.1-16, 2017. [3] Shogo Suzuki, Hideaki Okada, Kai Yabumoto, Seiju Matsuda, Yuki Mima, Noriaki Kimura, and Kenjiro Kimura, “Non-destructive visualization of short circuits in lithium-ion batteries by a magnetic field imaging system”, Japanese Journal of Applied Physics, Vol 60, No 5, pp.056502-1-4, 2021.

With the rapid spread of electric vehicles and hybrid vehicles in recent years, the energy density of lithium-ion batteries, which are the power sources of them, tends to increase.This means that the risk of ignition is further increased as represented by some fire accident case of an EV vehicle that had taken long time to extinguish, and thus eventually makes the requirement of safety management in the battery manufacturing process be expected stricter.To prevent ignition due to internal short circuit of battery, and eliminate a short-life battery product, we have been developing a technology to non-destructively visualize the self-discharged part inside the storage battery. In this technology, on the first, electric current is applied to the battery from external power source, and the leakage magnetic field that generated due to the internal electric current in the battery is sensed on outside of the battery. Next, the electric current density distribution inside the battery can be reconstructed and visualized three-dimensionally by using the spatial distribution of the measured magnetic field as the boundary condition and solving the inverse problem analytically. To measure leakage magnetic field with high sensitivity, it is necessary to take steps against disturbances as like DC magnetic field derived from magnetism or magnetic materials (often Ni is used for the collector foil), and AC magnetic fields generated from external circuits. In this method, two steps are used in combination for detection sensitivity of the pico-tesla order; (1) An AC current is applied to the battery, and the AC magnetic field generated in synchronization is phase-detected. (2) Install a small coil near the sensor and generate a DC cancel magnetic field by feedback control. By this method, it is possible to detect only the AC magnetic field corresponding to the applied current with high sensitivity in the linear operating region of the magnetic sensor. In actual detection of the leakage magnetic field, a DC voltage that balances with the output voltage of the battery is applied to the AC output of the AC current source connected to the battery so that the SOC of the storage battery is kept constant voltage. In addition to the above, the frequency of the AC output is usually set to 10 Hz or less to avoid the shielding effects of electrodes and the metallic package of the battery.By these steps and scanning two-dimensional of magnetic sensors or using a sensor array in which magnetic sensors are arranged two-dimensionally, the spatial distribution of the two-dimensional magnetic field outside the storage battery can be obtained. Since the sensor detects only one direction component of magnetic field, changing the direction of the sensor by 90 ° is needed. On data processing, some realistic structural assumptions are required to solve the inverse problem. (1) Defining that the plane parallel to the storage battery electrode plane is the XY plane, the Z component of the magnetic field vector is zero around the battery, and only X component and Y component remains as magnetic field vector components generated from internal current of the battery. (2) The thickness of the battery is sufficiently smaller than the size of the battery in the plane direction, that is, the three-dimensional current in the battery is confined in the thin two-dimensional plane. In the first step of the reconstruction, under the fact of (1), Laplace's equation is analytically solved in the "free space from the measurement surface to just above the electrode surface in the battery, without a magnetic source", and derive the two-dimensional magnetic field distribution directly above the electrode surface. In the next step, it is possible to obtain a three-dimensional current distribution inside the battery by analytically solving the Poisson-type equation and the electric current continuity equation under the realistic structural assumption of (2) with first calculation result as the boundary condition. In the presentation, we will introduce in detail the experiment and data processing for identifying the self-discharge point with this technology, including examples of visualizing the magnetic field distribution and current density distribution inside a battery after aging test.

To develop a high-density and long-life lithium-ion battery, a technology is needed that allows non-destructive visualization of the spatial distribution of deteriorated parts after cycle test. In the present study, we measured the distribution of the magnetic field leaking from the lithium-ion battery during its operation. Based on the measurement results, we evaluated the current density distribution inside a battery using the electric current reconstruction process. With respect to the changes in an internal state of the lithium-ion battery associated with cycle deterioration, we successfully visualized the spatial changes in the conductivity distribution inside the lithium-ion battery., 11 pages, 5 figures, letter

In this paper, we demonstrate various electric current imaging using electromagnetic field reconstruction method, and show its capability of reducing stray magnetic field effect.