Masaki Sekino

The University of Tokyo, Edo, Tōkyō, Japan

Are you Masaki Sekino?

Claim your profile

Publications (126)179.65 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To measure electrophysiological signals from the human body, it is essential to establish stable, gentle and nonallergic contacts between the targeted biological tissue and the electrical probes. However, it is difficult to form a stable interface between the two for long periods, especially when the surface of the biological tissue is wet and/or the tissue exhibits motion. Here we resolve this difficulty by designing and fabricating smart, stress-absorbing electronic devices that can adhere to wet and complex tissue surfaces and allow for reliable, long-term measurements of vital signals. We demonstrate a multielectrode array, which can be attached to the surface of a rat heart, resulting in good conformal contact for more than 3 h. Furthermore, we demonstrate arrays of highly sensitive, stretchable strain sensors using a similar design. Ultra-flexible electronics with enhanced adhesion to tissue could enable future applications in chronic in vivo monitoring of biological signals.
    Nature Communications 12/2014; 5:5898. · 10.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Previously we proposed an eccentric figure-eight coil that can cause threshold stimulation in the brain at lower driving currents. In this study, we performed numerical simulations and magnetic stimulations to healthy subjects for evaluating the advantages of the eccentric coil. The simulations were performed using a simplified spherical brain model and a realistic human brain model. We found that the eccentric coil required a driving current intensity of approximately 18% less than that required by the concentric coil to cause comparable eddy current densities within the brain. The eddy current localization of the eccentric coil was slightly higher than that of the concentric coil. A prototype eccentric coil was designed and fabricated. Instead of winding a wire around a bobbin, we cut eccentric-spiral slits on the insulator cases, and a wire was woven through the slits. The coils were used to deliver magnetic stimulation to healthy subjects; among our results, we found that the current slew rate corresponding to motor threshold values for the concentric and eccentric coils were 86 and 78 A/µs, respectively. The results indicate that the eccentric coil consistently requires a lower driving current to reach the motor threshold than the concentric coil. Future development of compact magnetic stimulators will enable the treatment of some intractable neurological diseases at home. Bioelectromagnetics. © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 11/2014; · 1.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We developed an MRI-compatible, ultra-thin, flexible stimulator array for the rat brain and performed functional MRI (fMRI) acquisition during direct electrical stimulation of the brain. This technique measured brain activity evoked by direct stimulation of the motor and the somatosensory cortex. In order to avoid MR signal loss due to interferences with the main static field and RF field in the MRI system, the stimulator array was made from a non-magnetic gold electrode of 100-nm thickness on a 2-um-thick parylene substrate. By using this stimulator array, MR images without signal loss around conducting electrode pads were acquired, and fMRI acquisition during concurrent electrical stimulation of the cerebral cortex was achieved. Neuronal activity propagated to distant brain areas from the stimulated motor cortex. Positive blood oxygenation level dependent (BOLD) signals were observed with direct stimulation of the motor cortex, while negative BOLD signals were observed with direct stimulation of the somatosensory cortex. Interestingly, the pattern of brain activity evoked by direct stimulation of the somatosensory cortex was different from that evoked by electrical stimulation of the forepaw.
    08/2014; 2014:6702-5.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Measuring the local pressure in blood vessels is valuable in the postoperative monitoring of aneurysms. However, implanting a conventional pressure sensor equipped with power and signal cables causes difficulties during the operative procedure and carries a risk of infection after the implantation. In this study, we developed a wireless, implantable, and flexible pressure sensor. A magnetic resonance imaging (MRI) system reads out the sensor output. The proposed wireless sensor is based on an LC resonant circuit with a spiral coil and a pressure-sensitive capacitor. The pressure-dependence of the capacitance affects the magnetic field produced by the spiral coil, changing the magnetization of the nearby sample that can be observed as a signal variation by MRI. We fabricated a prototype sensor using a capacitor with a silicone elastomer as the dielectric and a spiral coil made of gold. The maximum change in the capacitance was 8% under an external pressure of 20 kPa. A change in the thickness of the dielectric elastomer caused the capacitance to change, resulting in a signal variation detectable by MRI.
    08/2014; 2014:2338-41.
  • [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; · 3.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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; · 15.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 4.90 Impact Factor
  • Dongmin Kim, Takao Someya, Masaki Sekino
    [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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.
  • Y. Terao, M. Sekino, H. Ohsaki
    [Show abstract] [Hide abstract]
    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 06/2013; 23(3):5200904-5200904. · 1.32 Impact Factor
  • [Show abstract] [Hide abstract]
    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 06/2013; 23(3):3600705-3600705. · 1.32 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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; · 2.15 Impact Factor
  • [Show abstract] [Hide abstract]
    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 06/2012; 22(3):4400504-4400504. · 1.32 Impact Factor
  • Yutaka Terao, Masaki Sekino, Hiroyuki Ohsaki
    [Show abstract] [Hide abstract]
    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 06/2012; 22(3):5201904-5201904. · 1.32 Impact Factor
  • [Show abstract] [Hide abstract]
    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). · 2.19 Impact Factor
  • [Show abstract] [Hide abstract]
    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. · 2.02 Impact Factor

Publication Stats

533 Citations
179.65 Total Impact Points


  • 2002–2014
    • The University of Tokyo
      • • Department of Electrical Engineering and Information Systems
      • • Department of Advanced Energy
      • • Faculty & Graduate School of Medicine
      • • Department of Radiology and Biomedical Engineering
      • • Department of Medical Engineering
      Edo, Tōkyō, Japan
  • 2011
    • National Institute of Occupational Safety and Health JAPAN
      Edo, Tōkyō, Japan