Masaki Sekino

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (118)153.54 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A 64-channel surface electromyogram (EMG) measurement sheet (SEMS) with 2 V organic transistors on a 1 μ m-thick ultra-flexible polyethylene naphthalate (PEN) film is developed for prosthetic hand control. The surface EMG electrodes must satisfy the following three requirements; high mechanical flexibility, high electrode density and high signal integrity. To achieve high electrode density and high signal integrity, a distributed and shared amplifier (DSA) architecture is proposed, which enables an in-situ amplification of the myoelectric signal with a fourfold increase in EMG electrode density. In addition, a post-fabrication select-and-connect (SAC) method is proposed to cope with the large mismatch of organic transistors. The proposed SAC method reduces the area and the power overhead by 96% and 98.2%, respectively, compared with the use of conventional parallel transistors to reduce the transistor mismatch by a factor of 10.
    IEEE Transactions on Biomedical Circuits and Systems 06/2014; · 2.74 Impact Factor
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    ABSTRACT: A unique form of adaptive electronics is demonstrated, which change their mechanical properties from rigid and planar to soft and compliant, in order to enable soft and conformal wrapping around 3D objects, including biological tissue. These devices feature excellent mechanical robustness and maintain initial electrical properties even after changing shape and stiffness.
    Advanced Materials 04/2014; · 14.83 Impact Factor
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    ABSTRACT: Neuroinflammation is associated with many conditions that lead to dementia, such as cerebrovascular disorders or Alzheimer's disease. However, the specific role of neuroinflammation in the progression of cognitive deficits remains unclear. To understand the molecular mechanisms underlying these events we used a rodent model of focal cerebral stroke, which causes deficits in hippocampus-dependent cognitive function. Cerebral stroke was induced by middle cerebral artery occlusion (MCAO). Hippocampus-dependent cognitive function was evaluated by a contextual fear conditioning test. The glial neuroinflammatory responses were investigated by immunohistochemical evaluation and diffusion tensor MRI (DTI). We used knockout mice for P2Y1 (P2Y1KO), a glial ADP/ATP receptor that induces the release of proinflammatory cytokines, to examine the links among P2Y1-mediated signaling, the neuroinflammatory response, and cognitive function. Declines in cognitive function and glial neuroinflammatory response were observed after MCAO in both rats and mice. Changes in the hippocampal tissue were detected by DTI as the mean diffusivity (MD) value, which corresponded with the cognitive decline at 4 days, 1 week, 3 weeks, and 2 months after MCAO. Interestingly, the P2Y1KO mice with MCAO showed a decline in sensory-motor function, but not in cognition. Furthermore, the P2Y1KO mice showed neither a hippocampal glial neuroinflammatory response (as assessed by immunohistochemistry) nor a change in hippocampal MD value after MCAO. In addition, wild-type mice treated with a P2Y1-specific antagonist immediately after reperfusion did not show cognitive decline. Our findings indicate that glial P2Y1 receptors are involved in the hippocampal inflammatory response. The findings from this study may contribute to the development of a therapeutic strategy for brain infarction, targeting the P2Y1 receptor.
    Journal of Neuroinflammation 07/2013; 10(1):95. · 4.35 Impact Factor
  • Dongmin Kim, Takao Someya, Masaki Sekino
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    ABSTRACT: We developed an experimental setup for magnetic resonance imaging (MRI) of rat brain slices maintained in a hemoglobin-free medium and showed that the MRI system has a sensitivity to magnetic fields of 10(-11) T. The originally developed non-magnetic sample holder consisted of a microelectrode array for recording neuronal potentials and perfusing channels for the medium. Because of the hemoglobin-free condition, the magnetic fields could be distinguished from the baseline signal fluctuations due to hemoglobin. A theoretical estimation of the signal-to-noise ratio showed a sensitivity of 3.3 × 10(-10) T. Parameter optimization using a 7-T MRI system with the developed sample holder resulted in an experimental sensitivity of 4.0 × 10(-10) T. These MRI sensitivities potentially enable us to detect weak magnetic fields arising from neuronal activities, and are sufficiently high for detecting neuronal magnetic fields of 1.4 × 10(-11) T generated in rat brain slices by averaging signals 810 times.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:1370-1373.
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    ABSTRACT: The identification of the sentinel lymph nodes that cause tumor metastasis is important in breast cancer therapy. The detection of magnetic fluid accumulating in the lymph nodes using a magnetic probe allows surgeons to identify the lymph nodes. In this study, we carried out numerical simulations and experiments to investigate the sensitivity and basic characteristics of a magnetic probe consisting of a permanent magnet and a small magnetic sensor. The measured magnetic flux density arising from the magnetic fluid agreed well with the numerical results. In addition, the results helped realize an appropriate probe configuration for achieving high sensitivity to magnetic fluid. A prototype probe detected magnetic fluid located 30 mm from the probe head.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:5485-5488.
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    ABSTRACT: Objective: To assess the pain-relieving effects of motor cortex electrical stimulation (MCS) and the predictive factors retrospectively.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:6163-6166.
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    ABSTRACT: PURPOSE: To evaluate the accuracy of an equilibrium magnetization (M(0) ) map obtained using a two-dimensional (2D) spoiled gradient-recalled echo (SPGR) pulse sequence with variable flip angle (VFA). MATERIALS AND METHODS: Single-slice 2D SPGR images of 4% agar gel phantoms with different gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) concentrations (0-1 mM) were obtained with a VFA (2-30°). The 2D SPGR-VFA data were acquired with different repetition times (TRs; 7.8-117.2 ms), Gaussian and sinc RF pulses, and different field strengths (4.7, 7, and 9.4 Tesla). M(0) and T(1) maps were calculated from the 2D SPGR-VFA data. M(0) and T(1) values were compared with those calculated from free-relaxed 2D gradient-recalled echo (GRE) images and inversion recovery-prepared 2D SPGR images. The M(0) and T(1) slice profiles were also investigated. RESULTS: Consistent M(0) values were obtained, regardless of the different Gd concentrations, TRs, and pulse sequences. The M(0) slice profiles calculated from the sliced SPGR-VFA data quantitatively reproduced those calculated from the free-relaxed sliced GRE. In contrast, the T(1) values calculated from the 2D SPGR-VFA data were underestimated at a high Gd concentration, short TR, and Gaussian RF pulse. CONCLUSION: M(0) values calculated from 2D SPGR-VFA images are highly quantitative. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 02/2013; · 2.57 Impact Factor
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    ABSTRACT: A surface electromyogram (EMG), which measures a voltage waveform produced by skeletal muscles on skin, is an important tool for applications detecting the human will of motion, such as for prosthetic hands and prosthetic legs. In the application to a prosthetic hand, a multipoint EMG measurement is required to precisely control the hand [1, 2]. Conventional multipoint measurements with a passive electrode array [1-3], however, have two problems: 1) Measurement over a long time period is annoying, because the EMG electrodes placed on the skin are rigid, and 2) the signal integrity of EMG is degraded, because the number of wires between the electrodes and the front-end circuits increases with increasing number of measurement points. To address these challenges, a surface EMG measurement sheet (SEMS) on which an EMG electrode array and a front-end amplifier array with 2V organic transistors are integrated on a 1μm-thick ultra-flexible film is developed to control prosthetic hands. The developed SEMS enables a comfortable long-time measurement without signal integrity degradation.
    Solid-State Circuits Conference Digest of Technical Papers (ISSCC), 2013 IEEE International; 01/2013
  • Y. Terao, M. Sekino, H. Ohsaki
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    ABSTRACT: This paper deals with the comparison of electromagnetic characteristics of 10 MW class direct-drive wind turbine generators for offshore wind farms. Four kinds of wind turbine generators including a conventional permanent magnet generator, a salient/nonsalient pole superconducting generator, and a fully superconducting generator are investigated. Electromagnetic characteristics for these generators have been investigated with FEM analysis. The results show that a fully and a salient pole type superconducting wind turbine generators have a potential for 10 MW class offshore wind turbine generators from the aspect of size and economical points.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):5200904-5200904. · 1.20 Impact Factor
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    ABSTRACT: A superconducting power cable is a prospective application of high-temperature superconductors. Although power cables using Bi2223 or YBCO wires have been developed in the world so far mainly for utility grid application, we focus attention on railway application of a superconducting power cable. We have studied how to introduce superconducting power cables effectively and economically to a dc electric railway. Numerical analysis models based on the MATLAB-Simulink are constructed for a dc electric feeder system of singe- and double-track railways. Tractive force and train resistance characteristics are modeled. Energy saving by the superconducting power cable is investigated with the influences of the number of substations, the train operation interval, etc., taken into account. The results show that the superconducting power cables can improve regeneration rate and system energy saving, and reduce the substation capacity very effectively. It will be also an advantage that if the transportation capacity of a railway line needs to be increased, the introduction of superconducting cables could achieve it without changing the existing substations along the line.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):3600705-3600705. · 1.20 Impact Factor
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    ABSTRACT: Neutron capture therapy (NCT) is a promising non-invasive cancer therapy approach and some recent NCT research has focused on using compounds containing gadolinium as an alternative to currently used boron-10 considering several advantages that gadolinium offers compared to those of boron. In this study, we evaluated gadolinium-entrapped liposome compound as neutron capture therapy agent by in vivo experiment on colon-26 tumor-bearing mice. Gadolinium compound were injected intravenously via tail vein and allowed to accumulate into tumor site. Tumor samples were taken for quantitative analysis by ICP-MS at 2, 12, and 24h after gadolinium compound injection. Highest gadolinium concentration was observed at about 2h after gadolinium compound injection with an average of 40.3μg/g of wet tumor tissue. We performed neutron irradiation at JRR-4 reactor facility of Japan Atomic Energy Research Institute in Tokaimura with average neutron fluence of 2×10(12) n/cm(2). The experimental results showed that the tumor growth suppression of gadolinium-injected irradiated group was revealed until about four times higher compared to the control group, and no significant weight loss were observed after treatment suggesting low systemic toxicity of this compound. The gadolinium-entrapped liposome will become one of the candidates for Gd delivery system on NCT.
    Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie 12/2012; · 2.24 Impact Factor
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    ABSTRACT: In recent years, optical stimulation of neurons that bear a light-gated cation channel, "Optogenetics", has opened a new avenue for exploring neuronal connectivity of the nervous system. In this study, we applied a technique, "Opto-fMRI", which combined optogenetics with blood oxygenation level-dependent (BOLD) functional MRI (fMRI), for examining the neuronal connectivity of the hippocampal formation in rats. Although the hippocampal formation is very important for memory formation and retrieval, there is little information on its neuronal connectivity, especially on its longitudinal axis of connection. For this purpose, we utilized a transgenic rat strain, expressing the light-gated cation channel channelrhodopsin-2 (ChR2) under the regulation of the Thy1.2 promoter which permits the expression of the integrated gene in neurons. After optical stimulation targeting the dentate gyrus of the transgenic rat, we detected BOLD response of not only the dentate gyrus (DG) but also at the CA3 area. In addition, we detected the longitudinal-axis activation of the hippocampus after optical stimulation. Our study suggests that Opto-fMRI could be a tool for exploring the neuronal connectivity of the hippocampal formation, to understand the neural basis of memory formation and retrieval.
    Neuroscience Research 09/2012; · 2.20 Impact Factor
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    ABSTRACT: Repetitive transcranial magnetic stimulation (rTMS) is effective for treatment of several neurological and psychiatric diseases. We proposed an eccentric figure-eight coil, which induces strong eddy currents in the target brain tissue. In this study, numerical analyses were carried out to obtain magnetic field distribution of the eccentric figure-eight coil and eddy current in the brain. The analyses were performed with various coil design parameters, such as the outer and inner diameters and number of turns, to investigate the influence of these parameters on the coil characteristics. Increases in the inner diameter, outer diameter, and number of turns caused increases in the maximum eddy current densities. Coil inductance, working voltage, and heat generation also became higher with the increases in these design parameters. In order to develop a compact stimulator system for use at home, we need to obtain strong eddy current density, keeping the working voltage as low as possible. Our results show that it is effective to enlarge the outer diameter.
    Journal of Applied Physics 03/2012; 111(7). · 2.21 Impact Factor
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    ABSTRACT: One major effect caused by the different chemical shift frequencies of water and fat is the misregistration between the two components in MR images. Methods to correct misregistration are required in clinical MRI for accurate localization and artifact reduction. One of the methods uses the images scanned at opposite readout gradients to separate water and fat signal in the k-space. Its signal-to-noise ratio (SNR) achieves maximum when misregistration is around 0.9 pixels and deteriorates rapidly as the misregistration gets larger. In this work, we proposed a method to correct the chemical shift misregistration by using two data sets acquired at two different bandwidths. It is more generalized and flexible than the former method of opposite readout gradients and covers the former one as a special case. In both simulation and experiment, the new method is proved to be capable of correcting large chemical shift misregistration and maintain a good SNR.
    Magnetic Resonance Imaging 02/2012; 30(4):583-8. · 2.06 Impact Factor
  • Loïc Quéval, Masaki Sekino, Hiroyuki Ohsaki
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    ABSTRACT: A coupled finite element phase-domain model for superconducting synchronous machine is presented. It allows fast and accurate prediction of the transient and steady-state behavior of grid-connected machines. On the one hand, the machine self and mutual inductances as function of rotor angle are obtained from static finite element analysis. On the other hand, the machine is represented by a lumped-parameter phase-domain model. This approach offers two main advantages. Firstly, as opposed to the classical qd model, the phase-domain model takes into account inductance space harmonics. Secondly, it allows easy and efficient simulation of machine transients with the same accuracy as the one that could be obtained with a computationally expensive full finite element model. To show the flexibility of the proposed method, it is applied to an air-cored high temperature superconducting 10 MW class wind turbine generator with double layer distributed three-phase armature windings connected to the grid through an AC/DC/AC converter.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):5200804-5200804. · 1.20 Impact Factor
  • Yutaka Terao, Masaki Sekino, Hiroyuki Ohsaki
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    ABSTRACT: We have studied a 10 MW class fully superconducting synchronous machine for direct-drive wind turbine generators. This machine has been designed using two kinds of superconducting wires. Multifilament ${\rm MgB}_{2}$ wires have been used for armature windings. The DC field coils of the machine rotor are made of HTS tapes. Electromagnetic design of the generators has been carried out by FEM analysis. Analysis results show that 10 MW output is achievable with less use of HTS tapes than wind turbine generators having superconducting field coils and copper armature windings. Then, calculated AC losses are low.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):5201904-5201904. · 1.20 Impact Factor
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    ABSTRACT: Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive treatment for neurological and psychiatric diseases. We proposed an eccentric figure-eight coil which induces strong eddy currents in the target tissue at lower driving currents. In this study, numerical analyses were carried out to obtain magnetic field distribution of the eccentric figure-eight coil, eddy current distribution in the brain, and circuit characteristics. The analyses were performed with varied design parameters to show the influence of these parameters on coil characteristics. A prototype eccentric coil and driving circuit were fabricated. The coil generated a magnetic field of 1.7 T at the maximum output level of stimulator.
    Complex Medical Engineering (CME), 2012 ICME International Conference on; 01/2012
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    ABSTRACT: This paper presents magnetic-field distributions generated by screening currents flowing in short and straight multiple coated conductors exposed to a high magnetic field. The purpose of this study is to understand interactions between the magnetic field and the screening currents flowing in the coated conductors. In this paper, we suggest a method for calculating the magnetic-field distributions from current distributions. The method takes into account of the mutual screening current in the coated conductors. The magnetic-field distributions estimated using the method are in agreement with the experimental results. In addition, the current distributions inducing the magnetic-field distributions are described.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):4400504-4400504. · 1.20 Impact Factor
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    ABSTRACT: We have studied how to introduce superconducting power cables effectively and economically to a DC electric railway. Numerical analysis models were constructed, and the energy saving by the superconducting power cable was investigated with the influences of the number of substations, the train operation interval, the energy storage, etc. also taken into account. The results show that the superconducting power cables can improve regenerative energy and system energy saving, and reduce the substation capacity.
    Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2012 International Symposium on; 01/2012
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    ABSTRACT: We are developing stimulation coil navigation systems for home use of repetitive transcranial magnetic stimulation (rTMS). rTMS is effective for intractable diseases of the nervous system. However, the effects of rTMS last only for several hours, requiring a continuing daily rTMS therapies in a nearby clinic. A magnetic navigation system, the present system for fulfilling such needs, uses downsized, lightweight, low-cost magnetic sensors with datasets relating the magnetic field to the 3D position of the stimulation coil instead of the complicated handling and operation of large-scale and expensive devices or systems like a 3D position-measurement device. This system has been modified for home use and is easily available to non-medical staff. However, in a hospital, a large number of datasets, at least 500, is required, so collecting datasets might be a burden for the physician. To solve this problem, this paper proposes a method for extracting the necessary datasets for navigation. In the proposed method, many more datasets, which can handle any shape of a patient's head, are prepared in advance. The physician then collects only a few samples in the hospital. The system extracts the remaining datasets necessary for navigation by applying geometric model approximations like Delaunay triangulation or the ellipsoid model to the data for these samples. We evaluate the efficiency of the proposed method by a simulation of extracting datasets and navigating using a head model. The proposed method reduces the number of datasets collected by physicians from 500 to 10, thus reducing physicians' burdens.
    Complex Medical Engineering (CME), 2012 ICME International Conference on; 01/2012

Publication Stats

420 Citations
153.54 Total Impact Points

Institutions

  • 2002–2014
    • The University of Tokyo
      • • Department of Electrical Engineering and Information Systems
      • • Department of Nuclear Engineering and Management
      • • Department of Integrated Biosciences
      • • Graduate School of Frontier Sciences
      • • Faculty & Graduate School of Medicine
      • • Department of Bioengineering
      • • Department of Radiology and Biomedical Engineering
      Edo, Tōkyō, Japan
    • Emory University
      • Department of Neurology
      Atlanta, GA, United States
  • 2011
    • National Institute of Occupational Safety and Health JAPAN
      Edo, Tōkyō, Japan