Akihiko Kandori

University of Tsukuba, Tsukuba, Ibaraki-ken, Japan

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Publications (134)187.47 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: We developed a highly sensitive HTS SQUID system for liquid-phase detection of biological targets using magnetic markers. The SQUID consists of a ramp-edge Josephson junction made using an RE123-based multilayer process, and it showed a flux noise of 7.5 $muPhi_{0}/hbox{Hz}^{1/2}$ in the white noise region. The $1/f$ noise was 14 $muPhi_{0}/hbox{Hz}^{1/2}$ at $f = 1 hbox{Hz}$ when the SQUID was operated in AC bias mode. Using the SQUID system, we detected a biological target called biotin. In the experiment, biotins were fixed to a large polymer bead 3.3 $muhbox{m}$ in diameter. Streptavidin-coated magnetic markers were used for the detection. The bound and unbound (free) markers were magnetically distinguished using the difference in their Brownian relaxation time, i.e., without using a washing process to separate them. The minimum detectable number of biotins was as low as $2times 10^{4}$, corresponding to a sensitivity of $9.5times 10^{-19} hbox{mol/ml}$ . This result indicates that the developed method is highly sensitive. We also show the effect of the excitation field on the signals from free and bound markers for quantitative evaluation of the immunoassay.
    IEEE Transactions on Applied Superconductivity 01/2014; 24(4):1-5. · 1.20 Impact Factor
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    ABSTRACT: STUDY DESIGN:: Case-control study. OBJECTIVES:: The purpose of this study is to determine finger motion of patients with cervical myelopathy during finger tapping cycles. SUMMARY OF BACKGROUND DATA:: A major symptom of patients with compressive cervical myelopathy is finger clumsiness. Therefore, understanding finger motion is prerequisite to assessing the severity of myelopathy. The popular grip-and-release test evaluates only the number of motion cycles, which is insufficient to fully describe complex finger motion. METHODS:: Forty-three patients with cervical myelopathy and 41 healthy controls tapped their index fingers against their thumbs as rapidly as possible for 30 seconds and the motion was recorded by a magnetic sensor coil attached to the nail surface. Output signals were stored in a computer, which automatically calculated tapping frequency, distance moved, ratio of opening/closing velocity and the standard deviation (SD) of the tapping interval. RESULTS:: The SD of the tapping interval was significantly greater and all other measures were significantly smaller in patients with cervical myelopathy, than in healthy controls. All indices significantly improved after surgical decompression of the cervical spine. Distance moved (Pearson's correlation coefficient: r=0.590, P<0.001) and the SD of the tapping interval (r=-0.451; P=0.002) were significantly correlated with the Japanese Orthopedic Association score (neurological scale). CONCLUSIONS:: The quantitative evaluation of finger paralysis was performed by this tapping devise. Speed and regularity in repetitive motion of fingers were correlated with the severity of cervical myelopathy.
    Journal of spinal disorders & techniques 04/2013; · 1.21 Impact Factor
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    ABSTRACT: A battery-operated wireless flux-locked-loop (FLL) circuit for operating a high-Tc superconducting quantum interference device (SQUID) was developed and tested. This wireless battery-type FLL circuit consists of an FLL unit and a PC interface. A local area network with the TCP-IP protocol for wireless mode was used for communication between the PC interface and a controlling PC. The battery unit can power the FLL circuits for four hours. The FLL circuit had two bias modes: ac and dc. When the wireless-battery-type FLL circuit was implemented in a SQUID, the system noise generated by a wireless network became intrinsic high-Tc SQUID noise. Also, a 1/f noise was reduced in the case of the ac-bias-current mode. Consequently, the wireless-battery-type FLL circuit can operate a high-Tc SQUID with high sensitivity.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):1601204-1601204. · 1.20 Impact Factor
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    ABSTRACT: We have developed a microtesla nuclear magnetic resonance (NMR) system with a low- Tc superconducting quantum interference device gradiometer. We used it to simultaneously measure the free induction decay (FID) signals of water (15 ml) and perfluorooctane (15 ml). The static field and prepolarization field were 50 μT and 17 mT, respectively. The gradiometer was an axial-second-order type with a diameter of 50 mm and a baseline of 70 mm. NMR spectra were obtained by fast Fourier transformation of the FID signal. Two peaks, one for protons and one for fluorine nuclei, were clearly obtained without averaging. These results demonstrate that the developed microtesla NMR system can simultaneously detect NMR signals originating from multiple nuclei.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):1600904-1600904. · 1.20 Impact Factor
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    ABSTRACT: We developed a magnetic nanoparticle (MNP) imaging system that uses the harmonic signals of MNPs on the basis of their nonlinear magnetization curves. By measuring the harmonic signals, the interference of the excitation field can be significantly decreased, so the detection sensitivity can be improved. First, we obtained a contour map of the signal field from the MNPs, from which we estimated their positions. We could detect 100 μg of MNPs located at z=30 mm below the pickup coil with a signal-to-noise ratio of 4. Next, we analyzed the contour map using a mathematical technique called singular value decomposition (SVD) in order to improve the spatial resolution of the estimated position. Using the SVD method, we converted the field map to the MNP distribution. We could clearly distinguish two MNP samples separated by x=20 mm and located at Δz=20 mm. This simple detection system will be useful for medical applications such as sentinel lymph node detection.
    IEEE Transactions on Magnetics 11/2012; 48(11):3776-3779. · 1.42 Impact Factor
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    ABSTRACT: The correlation between neuronal activity and cortical hemodynamics, namely, neurovascular coupling (NVC), is important to shed light on the mechanism of a variety of brain functions or neuronal diseases. NVC can be studied by simultaneously measuring neuronal activity and cortical hemodynamics. Consequently, noninvasive measurements of the NVC have been widely studied using both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). However, electromagnetic interference between EEG and fMRI is still a major problem. On the other hand, near-infrared spectroscopy (NIRS) is another promising tool for detecting cortical hemodynamics because it can be combined with EEG or magnetoencephalography (MEG) without any electromagnetic interference. Accordingly, in the present study, a simultaneous measurement system-combining an unshielded MEG using a two-dimensional gradiometer based on a low-Tc superconducting quantum interference device (SQUID) and an NIRS using nonmagnetic thin probes-was developed. This combined system was used to simultaneously measure both an auditory-evoked magnetic field and blood flow change in the auditory cortex. It was experimentally demonstrated that the combined unshielded MEG/NIRS system can simultaneously measure neuronal activity and cortical hemodynamics.
    Journal of Biomedical Optics 10/2012; 17(10):107001-1. · 2.88 Impact Factor
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    ABSTRACT: We propose a linear discriminant regression analysis (LDRA) that provides an estimated severity marker for discriminating between healthy and patient groups and estimating severities of the patient group simultaneously. This method combines an evaluation function for discriminating between two groups and one for estimating severities of one group. The combined function is optimized to obtain an equation for calculating estimated severities. The method was evaluated with finger-tapping data of healthy and Parkinson's disease (PD) groups and PD severities assessed by a doctor. As a result, the discrimination ability of LDRA (AUC: 0.8835) was higher than that of discriminant analysis (DA. AUC: 0.8442), which is a conventional method for classification, and the regression ability of LDRA (mean square error (MSE): 1.27) was superior to that of multiple regression analysis (MRA. MSE: 1.68), which is a conventional method for regression. The results show that LDRA is an effective method for estimating the presence and severity of Parkinson's disease.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:4315-8.
  • Ryuzo Kawabata, Kyoya Fukuda, Akihiko Kandori
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    ABSTRACT: The magnetic resonance spectra of 133Cs vapor were obtained using a D1 transition, a D2 transition, and a combination of D1 and D2 transitions. Maximum intensity (Imax) and line width (Δ f) in the spectra were measured, and an ``α value'' (i.e., Imax/Δ f) was defined as an appropriate figure of merit for an optically pumped magnetometer (OPM). The α value obtained using the combination of D1 and D2 transitions was tenfold larger than that obtained using the D1 transition and 160 times larger than that obtained using the D2 transition. This result indicates that using the combination of D1 and D2 transitions improves the sensitivity of an OPM.
    Japanese Journal of Applied Physics 08/2012; 51(8):2404-. · 1.07 Impact Factor
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    ABSTRACT: A one-channel low temperature superconductor superconducting quantum interference device system comprising a second-order axial gradiometer with a sensing area of 10 mm × 190 mm was developed. The gradiometer was mounted in a liquid-helium dewar (450-mm diameter; 975-mm length), with a gap of 12 mm between the pickup coil and the dewar-tail surface. The magnetic field sensitivity was measured to be 16 fT/Hz(1/2) in the white noise regime above 2 Hz. The system was used to measure stainless steel particles of different sizes passing through the sensing area. A 100-μm diameter SUS304 particle was readily detected passing at different positions underneath the large pickup coil by measuring its 1.3-pT magnetic field. Thus, the system was shown to be applicable to quality control of lamination sheet products such as lithium ion batteries.
    The Review of scientific instruments 07/2012; 83(7):076108. · 1.52 Impact Factor
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    ABSTRACT: BACKGROUND: Despite the informative nature of atrial fibrillation (AF) electrograms, electrophysiological aspects of predicting reversal of structural remodeling of the left atrium (LA) have not been evaluated. OBJECTIVES: To identify predictors of reverse remodeling after restoration of sinus rhythm by catheter ablation in patients with persistent AF. METHODS: This study included 90 patients with persistent AF and enlarged LA (left atrial volume indexed to body surface area [LAVi] ≥32 mL/m(2)). LAVi was measured by echocardiography before ablation and 12 months after sinus rhythm restoration. We divided 73 (81%) patients free from recurrences into 2 groups according to reduction in LAVi: responders, reduction ≥23% (n = 35); nonresponders, reduction <23% (n = 38). Serological testing and electrophysiological characteristics on electrocardiogram and magnetocardiogram were analyzed. RESULTS: LAVi decreased from 43 ± 12 to 27 ± 7 mL/m(2) in responders and from 37 ± 8 to 33 ± 8 mL/m(2) in nonresponders. Higher LAVi at baseline (P = .01), lower age (59 ± 7 years vs 63 ± 7 years; P <.05), higher brain natriuretic peptide level (median = 92, interquartile range [IQR] = 98 pg/mL vs median = 60, IQR = 64 pg/mL; P = 0.01), higher atrial natriuretic peptide level (median = 73, IQR = 74 pg/mL vs median = 54, IQR = 70 pg/mL; P = .02), and higher organization index of AF signals (0.51 ± 0.11 vs 0.42 ± 0.09; P = .0001) were observed in responders. There was a linear correlation between organization index and % reduction in LAVi (R = 0.63; P <.0001). Multiple linear regression analysis showed relations between reverse remodeling and age (η = -0.28; P = .002), atrial natriuretic peptide level (η = 0.21; P = .03), and organization index (η = 0.53; P <.0001). CONCLUSIONS: Electrogram organization was a robust predictor of reverse remodeling of the enlarged LA after sinus rhythm restoration by catheter ablation in patients with persistent AF.
    Heart rhythm: the official journal of the Heart Rhythm Society 06/2012; · 4.56 Impact Factor
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    ABSTRACT: Differences in electrical properties between left and right atria (LA and RA) after pulmonary vein isolation (PVI) for atrial fibrillation (AF) are currently poorly understood. Magnetocardiograms were used to investigate the effect of PVI on bi-atrial magnetic field changes and their relationship to clinical outcomes. This study included 71 patients undergoing PVI for paroxysmal AF. Magnetocardiograms were recorded at baseline and 1 day, 8 weeks, and 24 weeks after ablation. Peak magnitude of LA and RA segments on P waves was separately compared before and after PVI. During a 16-month post-ablation period, 53 (75%) patients were free from AF recurrences. LA magnetic strength in patients without recurrence persistently decreased for 24 weeks and was significantly lower at 8 weeks than that in patients with recurrence (1.28±0.69 vs. 1.74±0.71 pico-Tesla, P=0.02). RA magnetic strength in patients with recurrence persistently rose for 24 weeks and was significantly higher at 8 weeks than that in patients without recurrence (2.17±0.82 vs. 3.00±1.12 pico-Tesla, P=0.001). Multivariate analysis showed RA magnetic strength at 8 weeks to be the strongest predictor of AF recurrence (odds ratio=3.335; 95% confidence interval=1.181-9.416; P=0.02). PVI resulted in distinct changes in magnetic strength in both the LA and the RA. A persistent rise in RA magnetic strength might be a robust predictor of AF recurrence after ablation.
    Circulation Journal 04/2012; 76(7):1601-8. · 3.58 Impact Factor
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    ABSTRACT: We developed a compact moving-sample magnetometer that uses a high-temperature superconductor--superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1× 10-7 emu.
    Japanese Journal of Applied Physics 04/2012; 51(4):6601-. · 1.07 Impact Factor
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    ABSTRACT: We characterized the magnetic markers used in biological immunoassays based on Brownian relaxation. Because the markers are composed of aggregated nanoparticles, i.e., magnetic nanoclusters, we first clarified their magnetic properties using AC susceptibility measurements, magnetization (M--H) curves, and magnetic relaxation properties. Analyzing the experimental results, we obtained the key parameters for the immunoassay, i.e., hydrodynamic diameter dh, magnetic moment mB, and anisotropy energy EB of the markers. Because these parameters were distributed in practical samples, we took their distribution into account in the analysis. Next, we showed the relationship between these parameters obtained from different samples. It was shown that mB increased approximately in proportion to dh. On the other hand, no clear correlation between mB and EB was obtained. These results were very different from those expected from single-domain nanoparticles and must be taken into account when magnetic markers are used in immunoassays based on Brownian relaxation.
    Japanese Journal of Applied Physics 02/2012; 51(2):3002-. · 1.07 Impact Factor
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    ABSTRACT: We developed a compact DC magnetometer using a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) to measure very weak magnetic signals from samples such as paramagnetic and diamagnetic materials. The samples were rotated in the DC magnetic field that was detected by a normal conductive pick-up coil. The detected signal was transferred to an input coil that was inductively coupled to the SQUID. To clarify the basic characteristics of this system, the magnetic signal from a magnetic material was measured by varying the sample position and rotation speed. Then, the magnetic signal from pure water was measured under the optimized condition and a very weak magnetic signal from pure water was successfully detected. Therefore, the developed system could be applied to various non-destructive evaluation systems.
    Superconductor Science and Technology 01/2012; 25(4). · 2.76 Impact Factor
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    ABSTRACT: A magnetic swallowing-detection system that can detect swallowing sounds and measure the distance between two magnetic coils was developed to detect the swallowing function non-invasively. The coils were set on both sides of the thyroid cartilage, and the distance between them changes in accordance with the movement of the thyroid cartilage. Swallowing sounds were detected by a piezoelectric microphone attached to the neck. The coils and microphone were installed in a holding unit that can be positioned at the front of the neck. The system was simultaneously used with videofluorography (VF) to measure nine healthy subjects while they swallowed liquid barium. To evaluate the correlation between the swallowing event detected by the magnetic swallowing-detection system and the swallowing event obtained from VF, two-dimensional positions of the hyoid bone in each VF image were detected. Based on the detection results, the swallowing starting time that was detected by the magnetic swallowing-detection system coincided with that determined from VF, namely, $38{\pm}172~{\hbox {ms}}$. The coincidence among the peak time point of VF, that of the distance between the magnetic coils, and that of the swallowing sound appeared to have an intraclass correlation coefficient of 0.9. Correlation between the peak time points of the VF tracking waveforms, the peak time points of distance between the magnetic coils, and the peak timing of the swallowing sound had an intraclass correlation coefficient of 0.9. It can be concluded that the magnetic swallowing-detection system can detect swallowing movements simply and non-invasively without x-ray exposure.
    IEEE Sensors Journal 01/2012; 12(4):805-811. · 1.48 Impact Factor
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    ABSTRACT: We have developed a liquid-phase immunoassay technique using Brownian relaxation of magnetic markers. In this method, biological targets are fixed on the surface of large polymer beads whose size is typically a few μm. When the markers are bound to the targets, their Brownian relaxation time is dominated by that of the polymer bead, becoming much longer than that of unbound (free) markers. The resulting difference between the magnetic properties of the bound and free markers was detected by relaxation measurements. Therefore, we can magnetically distinguish between the bound and free markers, i.e., we can omit a time consuming washing process called bound/free separation. We developed a detection system using a magneto-resistive (MR) sensor and showed that we can detect 1.4 × 10<sup>7</sup> bound markers in 60 μl of solution. If we assume that a single marker is bound to a single target, this sensitivity can be expressed as 3.8 × 10<sup>-16</sup> mol/ml (or 0.38 fmol/ml) in terms of the molecular-number concentration. We also demonstrated the detection of biological targets called biotins, which were conjugated on the surface of the polystyrene beads with a diameter of 3.3 μm. A strong relationship was obtained between the number of bound markers and the number of biotin-conjugated polymer beads, which confirmed the validity of the present method.
    IEEE Transactions on Magnetics 11/2011; · 1.42 Impact Factor
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    ABSTRACT: This paper proposes the CPG synergy model--a biomimetic rhythm generator model based on central pattern generators (CPGs) and muscle synergy theory to enable evaluation of rhythmic motions with non-stationary characteristics such as human finger tapping movements. The model consists of multiple CPGs to approximate the complex rhythmic movement of humans, and has the potential to allow evaluation of abnormal movements in patients with motor function impairments such as Parkinson's disease (PD). To verify the validity of the proposed model, comparison experiments were conducted using model parameters (i.e., synergies, weight coefficients and time-shift parameters) extracted from finger tapping movements performed by individuals in a healthy subject group and a PD patient group. The results showed that the number of synergies, the second moment of synergy shapes and the coefficient of variation of maximum weight coefficients show significant differences for each subject group, and indicated that the model could be used to evaluate irregular rhythmic movements as well as regular ones.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:4443-8.
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    ABSTRACT: We have designed and tested an HTS SQUID magnetometer using the resonant coupling of a copper pickup coil cooled at T = 77 K. The coil was made of a twisted multi-filamentary wire so as to reduce the ac resistance. We first showed that the ac resistance of the coil became higher than the dc resistance because of the eddy current loss of the coil. We clarified the dependence of the ac resistance on the parameters of the coil and obtained an empirical expression for the ac resistance. Next, we constructed a magnetometer using a pickup coil with the average diameter D = 50 mm and number of turns N =150 . The pickup coil with an inductance of Lp = 1.05 mH was connected to an input coil through a resonant capacitance of C = 0.29 μF. The HTS SQUID was magnetically coupled to the input coil with a mutual inductance of M = 500 pH. The estimated magnetic field noise of the magnetometer was approximately 2.5 fT/Hz <sup>1/2</sup> at the resonant frequency of f = 9.05 kHz. The Q value of the resonant circuit was 180. The experimental results agreed well with the designed values. The obtained high sensitivity of the magnetometer will be useful for low frequency applications such as low-field NMR.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: The aim of this study was to develop a method for converting the pseudo two-dimensional current given by a current-arrow map (CAM) into the physical current. The physical current distribution is obtained by the optimal solution in a least mean square sense with Tikhonov regularization (LMSTR). In the current dipole simulation, the current pattern differences (ΔJ) between the results of the CAM and the LMSTR with several regularization parameters (α = 10(-1)-10(-15)) are calculated. In magnetocardiographic (MCG) analysis, the depth (z(d)) of a reconstruction plane is chosen by using the coordinates of the sinus node, which is estimated from MCG signals at the early p-wave. The ΔJs at p-wave peaks, QRS-complex peaks, and T-wave peaks of MCG signals for healthy subjects are calculated. Furthermore, correlation coefficients and regression lines are also calculated from the current values of the CAM and the LMSTR during p-waves, QRS-complex, and T-waves of MCG signals. In the simulation, the ΔJs (α ≈ 10(-10)) had a minimal value. The ΔJs (α = 10(-10)) at p-wave peaks, QRS-complex peaks, and T-wave peaks of MCG signals for healthy subjects also had minimal value. The correlation coefficients of the current values given by the CAM and the LMSTR (α = 10(-10)) were greater than 0.9. Furthermore, slopes (y) of the regression lines are correlated with the depth (z(d)) (r = -0.93). Consequently, the CAM value can be transformed into the LMSTR current value by multiplying it by the slope (y) obtained from the depth (z(d)). In conclusion, the result given by the CAM can be converted into an effective physical current distribution by using the depth (z(d)).
    The Review of scientific instruments 01/2011; 82(1):014302. · 1.52 Impact Factor
  • Journal of Electrocardiology - J ELECTROCARDIOL. 01/2011; 44(2).

Publication Stats

672 Citations
187.47 Total Impact Points


  • 1999–2012
    • University of Tsukuba
      • Institute of Clinical Medicine
      Tsukuba, Ibaraki-ken, Japan
  • 1998–2012
    • Hitachi, Ltd.
      • Central Research Laboratory
      Tokyo, Tokyo-to, Japan
  • 2011
    • Kyushu University
      Hukuoka, Fukuoka, Japan
    • Nishinomiya Kyoritsu Neurosurgical Hospital
      Nishinomiya, Hyōgo, Japan
  • 2008–2011
    • Hiroshima University
      • Graduate School of Engineering
      Hiroshima-shi, Hiroshima-ken, Japan
  • 2010
    • Nagasaki International University
      • Faculty of Pharmaceutical Sciences
      Nagasaki-shi, Nagasaki-ken, Japan
  • 2009
    • Okayama University
      Okayama, Okayama, Japan
  • 1999–2006
    • Daiwa House Central Research Laboratory
      Edo, Tōkyō, Japan
  • 2001–2004
    • National Cerebral and Cardiovascular Center
      • Department of Cardiovascular Medicine
      Ōsaka, Ōsaka, Japan
  • 2002
    • Fujita Health University
      • Department of Surgery
      Toyohashi, Aichi-ken, Japan