研究者業績

山口 匡

ヤマグチ タダシ  (Tadashi Yamaguchi)

基本情報

所属
千葉大学 フロンティア医工学センター 教授
(兼任)工学研究院 教授
(兼任)医学部附属病院 超音波センター 教授
学位
博士(工学)(千葉大学)

J-GLOBAL ID
200901007599937458
researchmap会員ID
1000357236

外部リンク


論文

 157
  • Kenji YOSHIDA, Masaaki Omura, Shinnosuke Hirata, Tadashi YAMAGUCHI
    Japanese Journal of Applied Physics 2025年3月7日  
    Abstract This study investigates the dependence of the translational velocity of lipid-coated microbubbles in an ultrasound field on the viscosity of the surrounding Newtonian fluid. Plane burst waves with a center frequency of 7.34 MHz were used to uniformly drive microbubbles with a radius of 1.4 ± 0.3 m (mean ± standard deviation) in a flow channel. Bubbles were detected using the Doppler method using pulse waves with a center frequency of 5.2 MHz, and the velocities of individual bubbles were analyzed by tracking them in consecutive images. Examinations were conducted at various viscosities from 1 to 3 mPa∙s. The experimentally determined velocity–viscosity relationship qualitatively agreed with numerical simulations. This was written as a power-law dependence and used as a calibration curve to evaluate the local viscosity coefficient for the trajectories of individual bubbles. We succeeded in demonstrating viscosity imaging by multiplying the obtained viscosity coefficient with the bubble trajectories, convoluted with the point spread function of ultrasound imaging.
  • Miyu Nagaoka, Koichi Ito, Shinnosuke Hirata, Kenji YOSHIDA, Tadashi YAMAGUCHI
    Japanese Journal of Applied Physics 2025年2月14日  査読有り最終著者責任著者
    Abstract We conducted a fundamental study to elucidate the relationship between acoustic and electrical properties in the context of liver steatosis. The speed of sound, attenuation coefficient, conductivity, and relative permittivity were measured in rat livers with varying degrees of fat deposition. Fat deposition result in a decrease in the speed of sound, an increase in the attenuation coefficient, and reductions in conductivity and relative permittivity. However, no linear correlation was observed between these properties and fat content or droplet size individually. However, a notable correlation between changes in acoustic and electrical properties was identified when the structural and organizational effects of fat were considered in combination. Especially, attenuation changes were found to correlate with corresponding changes in electrical properties. These findings underscore the importance of comprehensively considering structural factors, such as fat droplet size and distribution, to better understand the physical mechanisms underlying the relationship between acoustic and electrical properties.
  • Masaaki Omura, Kunimasa Yagi, Ryo Nagaoka, Kenji Yoshida, Tadashi Yamaguchi, Hideyuki Hasegawa
    Ultrasonics 149 107589-107589 2025年1月30日  査読有り
    Hemorheological properties, such as erythrocyte aggregation can be assessed by ultrasonic backscatter coefficient analysis. In this study, a data-acquisition sequence with dual-frequency (dual-f) excitation was proposed to expand the ultrasonic frequency bandwidth with high-frame-rate imaging. The approach was experimentally validated using ex vivo porcine blood measurements and in vivo human imaging. The center frequency of the excitation wave was alternated between 7.8 (f1) and 12.5 (f2) MHz in the frequency spectral analysis using the reference phantom method. The frequency spectra revealed that the dual-f sequence achieved a bandwidth of 4.5-15 MHz at -20 dB, almost equivalent to those achieved with conventional single-frequency excitation (5.0-15 MHz) with a short-duration wave at 10 MHz (mono-f) in reference media with the sufficient condition of signal-to-noise ratio. The aggregation and disaggregation states of porcine blood suspended in high-molecular-weight dextran were determined by the isotropic diameter and packing factor using the structure factor size estimator. The discrimination performance of the dual-f approach increased, owing to the broadband frequency responses, in contrast with the limited performance of mono-f due to a low signal-to-noise ratio. This approach incorporating dual-f sequence is beneficial for obtaining robustly frequency spectra of hemorheological properties from in vivo scenarios.
  • Akiho Isshiki, Kisako Fujiwara, Takayuki Kondo, Kenji Yoshida, Tadashi Yamaguchi, Shinnosuke Hirata
    Journal of Medical Ultrasonics 52(1) 5-15 2024年11月23日  査読有り
    Abstract Purpose Early detection and quantitative evaluation of liver steatosis are crucial. Therefore, this study investigated a method for classifying ultrasound images to fatty liver grades based on echo-envelope statistics (ES) and convolutional neural network (CNN) analyses. Methods Three fatty liver grades, i.e., normal, mild, and moderate-to-severe, were defined using the thresholds of the magnetic resonance imaging-derived proton density fat fraction (MRI-PDFF). There were 10 cases of each grade, totaling 30 cases. To visualize the texture information affected by the deposition of fat droplets within the liver, the maps of first- and fourth-order moments and the heat maps formed from both moments were employed as parametric images derived from the ES. Several dozen to hundreds of regions of interest (ROIs) were extracted from the liver region in each parametric image. A total of 7680 ROIs were utilized for the transfer learning of a pretrained VGG-16 and classified using the transfer-learned VGG-16. Results The classification accuracies of the ROIs in all types of the parametric images were approximately 46%. The fatty liver grade for each case was determined by hard voting on the classified ROIs within the case. In the case of the fourth-order moment maps, the classification accuracy of the cases through hard voting mostly increased to approximately 63%. Conclusions The formation of parametric images derived from the ES and the CNN classification of the parametric images were proposed for the quantitative diagnosis of liver steatosis. In more than 60% of the cases, the fatty liver grade could be estimated solely using ultrasound images.
  • Jungtaek Choi, Jeffrey A. Ketterling, Jonathan Mamou, Cameron Hoerig, Shinnosuke Hirata, Kenji Yoshida, Tadashi Yamaguchi
    Sensors 24(22) 7118-7118 2024年11月5日  査読有り最終著者責任著者
    The objective of this work is to address the need for versatile and effective tissue characterization in abdominal ultrasound diagnosis using a simpler system. We evaluated the backscattering coefficient (BSC) of several tissue-mimicking phantoms utilizing three different ultrasonic probes: a single-element transducer, a linear array probe for clinical use, and a laboratory-made annular array probe. The single-element transducer, commonly used in developing fundamental BSC evaluation methods, served as a benchmark. The linear array probe provided a clinical comparison, while the annular array probe was tested for its potential in high-frequency and high-resolution ultrasonic observations. Our findings demonstrate that the annular array probe meets clinical demands by providing accurate BSC measurements, showcasing its capability for high-frequency and high-resolution imaging with a simpler, more versatile system.

MISC

 569
  • 大塚 武, 山口 匡, 蜂屋 弘之
    日本音響学会研究発表会講演論文集 1996(2) 1121-1122 1996年3月1日  
  • Pudjiatmoko, H Fukushi, Y Ochiai, T Yamaguchi, K Hirai
    MICROBIOLOGY AND IMMUNOLOGY 40(10) 755-759 1996年  
    The prevalence of anti-chlamydia antibodies was examined in 232 cat sera collected in 1985 and from 1993 to 1995 from laboratories and veterinary hospitals located in 11 prefectures of Japan. The antibodies were determined by an indirect microimmunofluorescence test using six strains of feline Chlamydia: one strain each of avian- and guinea pig-derived C. psittaci and one strain each of C. pecorum, C. pneumoniae and C. trachomatis. Positive rates of IgG antibodies to chlamydiae were 34.4% in 1985 and 16.5-21.4% from 1993 to 1995. Positive rates of IgM antibodies to chlamydiae were 8.2% in 1985 and 6.6-14.3% from 1993 to 1995. Variations in antibody reactivity to the different feline strains were observed. The results suggest the wide prevalence of chlamydial infection in cats in Japan, and antigenic diversity in the feline strains of C. psittaci.
  • H Sunaoshi, K Hattori, J Takamatsu, A Ando, H Wada, S Magoshi, T Yamaguchi, S Sato, S Nishimura, H Housai, S Hashimoto, R Yoshikawa, T Takigawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 34(12B) 6679-6683 1995年12月  
    A character beam calibration method has been developed for the electron beam exposure system EX-8D. The method concerns the character selection deflector, beam current density uniformity, beam size, direction, and position on the target. For the current density, the uniformity of less than 1.4% has been obtained in a 2-mm-square field. The beam size and the direction has been calibrated with an error of less than 1 nm in a 1-mu m-square character beam. The overall error of the resist pattern size exposed by the character beam was estimated to be 7.2 nm. For the beam position on the target, tile calibration accuracy of 0.023 mu m has been obtained by a pattern matching method. After applying the calibration, 0.15 mu m line-and-space patterns were exposed with good resolution by using the character beam. Also, a test pattern has been written with 0.02 mu m stitching accuracy between variable shaped and character beams.
  • Y MATSUSHITA, T UETANI, T KUNISATO, J SUZUKI, Y UEDA, K YAGI, T YAMAGUCHI, T NIINA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 34(4A) 1833-1834 1995年4月  
    Dependence of SiC blue light-emitting diode (LED) efficiency an the p-type layer growth temperature in the liquid-phase epitaxial process was investigated. The external quantum efficiency of LEDs fabricated at a lower growth temperature was higher than that of those fabricated at a conventional growth temperature of 1720 degrees C and maximized at a growth temperature of 1530 degrees C. In this study, luminous intensity of 32 mcd was obtained at a forward current of 20 mA (lambda(p) = 467 nm).
  • 山口匡
    超音波医学会 BT95-26 1995年  
  • T HO, KK HTWE, N YAMASAKI, GQ ZHANG, M OGAWA, T YAMAGUCHI, H FUKUSHI, K HIRAI
    MICROBIOLOGY AND IMMUNOLOGY 39(9) 663-671 1995年  
    Coxiella burnetii was isolated from raw milk (36/214, 16.8%) and uterus swab samples (13/61, 21.3%) originating from dairy cattle with reproductive disorders, aborted bovine fetus samples (2/4, 50%), mammary gland samples (4/50, 8%) originating from healthy dairy cattle, and tick samples (4/15, 26.7%) originating from 2 pastures. Fifty-nine strains had various degrees of pathogenicity, high (8; 13.6%), moderate (28; 47.5%) and low (23; 39%), for guinea pigs. The results of isolation suggested a high prevalence of Coxiella infection in dairy cattle with reproductive problems in Japan. Twelve strains (7, 2 and 3 strains from cattle, ticks and humans, respectively) and the reference Nine Mile strain of phases I and II were propagated in both yolk sacs of embryonated hen eggs and Buffalo green monkey (BGM) cell cultures. Protein profiles of these strains were similar to those of the reference strain of phase I. Lipopolysaccharide (LPS) profiles of 12 strains were similar to those of the reference strain of phase I and different from those of the reference strain of phase II. The LPS profiles of 12 strains suggested that these strains are associated with an acute form of Q fever.
  • K HATTORI, S MAGOSHI, H SUNAOSHI, H WADA, A ANDO, T YAMAGUCHI, S MIKAMI, S NISHIMURA, H HOUSAI, S HASHIMOTO, R YOSHIKAWA, T TAKIGAWA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 33(12B) 6966-6970 1994年12月  
    Self-diagnosis functions related to patterning accuracy are important techniques fur developing, improving and maintaining electron beam exposure systems. An evaluation method of beam position deviation has been developed to reduce fluctuation of patterning accuracy. High-frequency beam position deviation was detected by scan ning the beam on a W mark with subsequent fast fourier transform analysis. A magnetic field compensator has been developed to reduce low-frequency beam position deviations induced by ambient magnetic field changes. The beam position deviations of high- and low-frequency have been restricted to about 17 nm (3 sigma). A mark stand, which carries a height-changeable mechanism, was developed to calibrate the beam deflection accuracy depending on the Z direction. By applying the above diagnostic function, a main frame stitching accuracy of 32 nm has been achieved with short turnaround time.
  • N HIROTSU, T YAMAGUCHI, R HIDAKA, M TANAKA, Y KAWAI
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 33(5A) 2712-2717 1994年5月  
    To clarify the production mechanism of a large-diameter uniform electron cyclotron resonance (ECR) plasma generated by a circular TE01 mode microwave experimentally, the wave propagation characteristic in the plasma is measured with an interferometer. It is shown that a.microwave introduced into the chamber is transformed mainly into an electron cyclotron wave and then entirely absorbed around the resonance point. Furthermore, it is experimentally proven that the correspondence between the radial distribution of the electric field intensity of injected microwaves and that of waves propagating in plasma may depend on the magnetic field intensity around the injection point. It is also confirmed that it is necessary to optimize the magnetic field configuration to generate a uniform ECR plasma since the absorption region of microwaves is as wide as from omega/omega(ce) approximately 0.65 to adjacent to the resonance point.
  • Yamaguchi, T.
    Nippon Geka Gakkai zasshi 95(12) 899-910 1994年1月1日  
    A newly developed novel elastometric surgical elastoma based on reactive hydrophylic urethane was tested in vivo experiment of dog models for its anastomotic performances and functions at various periods. The carotid artery as well as the abdominal aorta were completely transected and reanastomosed by applying the adhesive materials. The serial studies on patency rate, tensile strength, elasticity as well as histopathological examinations were undertaken up to the longest period of 180 days after the implantation. The overall patency rate in carotid anastomosis was 93.9%, where in the abdominal aorta, 100% of patency rate was obtained. The tensile strength at the anastomosis surpassed the stress derived from pulsation and internal tension within 7 days of implantation. No significant change in stiffness parameter beta was observed in 180 days of implantation. Histopathological studies at the site of anasotmosis revealed the presence of mild inflammatory reaction in earlier phase and well healing of tissue without foreign body reaction in later period. This material proved to be an effective surgical adhesive in reference to the compliance mateching so as to facilitate to expect for the clinical application in cardiovascular surgical practice.
  • F SHIMIZU, M TAKASHIGE, S SAWADA, T YAMAGUCHI
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 62(8) 2964-2965 1993年8月  
  • T YASUDA, Y FUJII, T YAMAGUCHI
    PLANT AND CELL PHYSIOLOGY 26(3) 595-597 1985年  
    Coffea arabica leaf explants cultured on medium with 5 μM 6-benzyladenine (BA) as the sole plant growth regulator produced white friable calluses that formed somatic embryos. These calluses have been subcultured on the same medium for more than 2 years and maintain the ability to produce somatic embryos.

講演・口頭発表等

 449

担当経験のある科目(授業)

 20

共同研究・競争的資金等の研究課題

 44

社会貢献活動

 53