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Search Results: 1 - 10 of 933 matches for " Kazuki Shimada "
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Effect of Signal Filtering on Image Quality of Projection-Based Magnetic Particle Imaging  [PDF]
Kazuki Shimada, Kenya Murase
Open Journal of Medical Imaging (OJMI) , 2017, DOI: 10.4236/ojmi.2017.72005
Abstract: Purpose: Magnetic particle imaging (MPI) allows for imaging of the spatial distribution of magnetic nanoparticles (MNPs) in positive contrast, with high sensitivity, high spatial resolution, and high imaging speed. It is necessary to increase the signal-to-noise ratio to enhance the reliability of MPI. The purpose of this study was to investigate the effect of signal filtering on the image quality and quantitativity in projection-based MPI using phantoms. Materials and Methods: We fabricated two kinds of phantom (cylindrical tube phantom with a diameter of 6 mm and A-shaped phantom) and evaluated the effect of signal filtering in terms of root-mean-square (RMS) granularity and the correlation coefficient between iron concentrations of MNPs and average MPI values for four filter modes (THRU, BPF, BEF, and LPF). In the THRU mode, the signal input was output without passing through the filter. In the BPF mode, only the third-harmonic signal was passed using a band-pass filter (central frequency: 1200 Hz, band width: 1/3 octave). In the BEF mode, the first-harmonic signal was eliminated using a band-elimination filter (central frequency: 400 Hz, band width: 1/3 octave). In the LPF mode, only the signal with a frequency less than the third-harmonic frequency was passed using a low-pass filter (cut-off frequency: 1200 Hz, -24 ± 2 dB/octave). The RMS granularity was obtained by calculating standard deviations of the pixel values in the MPI image without MNPs, whereas average MPI values were obtained by drawing a circular region of interest with a diameter of 6 mm on the MPI image of the cylindrical tube phantom. Results: When using the filtered back-projection (FBP) method with a ramp filter for image reconstruction, the RMS granularity and correlation coefficient decreased in the order of THRU, BPF, BEF, and LPF. In the BPF mode, however, some artifacts were observed. When using the maximum likelihood-expectation maximization (ML-EM) algorithm with an iteration number of 15, the correlation coefficient decreased in the order of THRU, BPF, BEF, and LPF, whereas the RMS granularity did not largely depend on the filter mode and was significantly (p < 0.05) lower than that for the FBP method for all the filter modes. Conclusion: The BEF mode is adequate for the FBP method in projection-based MPI, whereas THRU is a best option in use of the ML-EM algorithm.
Lock-in-Amplifier Model for Analyzing the Behavior of Signal Harmonics in Magnetic Particle Imaging  [PDF]
Kenya Murase, Kazuki Shimada
Open Journal of Applied Sciences (OJAppS) , 2018, DOI: 10.4236/ojapps.2018.85014
Abstract: The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-amplifier model, the signal induced by magnetic nanoparticles (MNPs) in a receiving coil was multiplied with a reference signal, and was then fed through a low-pass filter to extract the DC component of the signal (output signal). The MPI signal was defined as the mean of the absolute value of the output signal. The magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively, and the strength of the selection magnetic field (SMF) in MPI was assumed to be given by the product of the gradient strength of the SMF and the distance from the field-free region (x). In addition, Gaussian noise was added to the signal induced by MNPs using normally-distributed random numbers. The relationships between the MPI signal and x were calculated for the odd- and even-numbered harmonics and were investigated for various time constants of the low-pass filter used in the lock-in amplifier and particle sizes and their distributions of MNPs. We found that the behavior of the MPI signal largely depended on the time constant of the low-pass filter and the particle size of MNPs. This lock-in-amplifier model will be useful for better understanding, optimizing, and developing MPI, and for designing MNPs appropriate for MPI.
Analysis of the Factors for Displacement of Earth Retaining Wall with Twin-Stepped Construction  [PDF]
Seiya Sakuma, Kazuki Maehara, Takahiro Funatsu, Akihiro Hamanaka, Takashi Sasaoka, Hideki Shimada
World Journal of Engineering and Technology (WJET) , 2019, DOI: 10.4236/wjet.2019.71007
Abstract: The demand for specific earth retaining wall method is increasing, along with the advancement and overcrowding of underground space use, such as the?presence of close structures, in an urban area. The method is named stepped-twin?retaining wall. The feature of this method is to have inner and outer retaining walls and excavate the ground by two-step in order to minimize the effect of the excavation on neighboring existing structures. However, the design of the earth retaining wall is currently carried out by individual engineers based on their own experience. Therefore, it is crucial that the standard method of retaining wall using a two-step construction is established. As the first step toward the standardization, evaluation of factors affecting the ground behavior of the earth retaining wall was carried out. In particular, we picked up four major considerable factors, which are horizontal distance between the outer and inner walls, depth of outer wall embedment, mechanical properties of soil. The evaluation was done by using two dimensional FEM analysis and the results were summarized to make clear the effect of each factor.
Disposition Kinetics of Taxanes in Peritoneal Dissemination
Ken'ichi Miyamoto,Tsutomu Shimada,Kazuki Sawamoto,Yoshimichi Sai,Yutaka Yonemura
Gastroenterology Research and Practice , 2012, DOI: 10.1155/2012/963403
Abstract: Treatment of cancers in the abdominal cavity, such as peritoneal dissemination, is difficult, but in principle intraperitoneal administration of anticancer drugs is expected to be preferable to systemic administration. Taxane anticancer drugs are used to treat gastric cancer patients with peritoneal dissemination. They are administered as micellar preparations, Taxol and Taxotere, which consist of paclitaxel in Cremophor EL (crEL) and docetaxel in Polysorbate-80 (PS-80), respectively. In this paper we review the disposition kinetics of taxane anticancer drugs after intraperitoneal administration in peritoneal dissemination patients and animal models and also discuss the effect of the surfactant vehicle on the behavior of taxanes.
Insulin-Producing Cells Regulate the Sexual Receptivity through the Painless TRP Channel in Drosophila Virgin Females
Takaomi Sakai, Kazuki Watanabe, Hirono Ohashi, Shoma Sato, Show Inami, Naoto Shimada, Toshihiro Kitamoto
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088175
Abstract: In a variety of animal species, females hold a leading position in evaluating potential mating partners. The decision of virgin females to accept or reject a courting male is one of the most critical steps for mating success. In the fruitfly Drosophila melanogaster, however, the molecular and neuronal mechanisms underlying female receptivity are still poorly understood, particularly for virgin females. The Drosophila painless (pain) gene encodes a transient receptor potential (TRP) ion channel. We previously demonstrated that mutations in pain significantly enhance the sexual receptivity of virgin females and that pain expression in painGAL4-positive neurons is necessary and sufficient for pain-mediated regulation of the virgin receptivity. Among the painGAL4-positive neurons in the adult female brain, here we have found that insulin-producing cells (IPCs), a neuronal subset in the pars intercerebralis, are essential in virgin females for the regulation of sexual receptivity through Pain TRP channels. IPC-specific knockdown of pain expression or IPC ablation strongly enhanced female sexual receptivity as was observed in pain mutant females. When pain expression or neuronal activity was conditionally suppressed in adult IPCs, female sexual receptivity was similarly enhanced. Furthermore, both pain mutations and the conditional knockdown of pain expression in IPCs depressed female rejection behaviors toward courting males. Taken together, our results indicate that the Pain TRP channel in IPCs plays an important role in controlling the sexual receptivity of Drosophila virgin females by positively regulating female rejection behaviors during courtship.
Simple Calculus of Resolving the Fiscal Policy Puzzle: The Role of Human Capital  [PDF]
Kazuki Hiraga
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.49093
Abstract: This paper investigates how much externality of human capital a la on-the-job training resolves the fiscal policy puzzle that is consistent with the empirical evidences which obtain the positive response of consumption and wage to increase of fiscal spending in general equilibrium model.
Simple Analysis of Dynamic Efficiency in Endogenous Fertility  [PDF]
Kazuki Hiraga
Theoretical Economics Letters (TEL) , 2015, DOI: 10.4236/tel.2015.54063
Abstract: This paper compares with two conditions of dynamic (in)efficiency, which is “traditional” and “modified” in overlapped generations (OLG) model with endogenous fertility. We show that both two conditions of dynamic efficiency have a bliss point which maximizes the utility at steady state in endogenous fertility.
Pre-operative diagnosis and successful surgery of a strangulated internal hernia through a defect in the falciform ligament: a case report
Hironori Shiozaki, Shintaro Sakurai, Kazuki Sudo, Gen Shimada, Hiroshi Inoue, Seiji Ohigashi, Gautam A. Deshpande, Osamu Takahashi, Hisashi Onodera
Journal of Medical Case Reports , 2012, DOI: 10.1186/1752-1947-6-206
Abstract: A 77-year-old Japanese woman presented to our emergency department with sudden hematemesis, occurring at least four to five times over a 12-hour period. No ulcer or gastrointestinal bleeding was detected on gastroendoscopy. A 40mm mass in the inferior lobe of the right lung was found on a chest X-ray, and our patient’s symptoms were therefore initially ascribed to aspirated blood from lung tumor-associated hemoptysis. However, our patient continued to show signs of severe abdominal pain and decreased urine output despite aggressive hydration, leading her examining physicians to search for a possibly severe, occult abdominal pathology. On emergent computed tomography imaging, we found an acute strangulated internal hernia within the falciform ligament. Diagnosis was made by helical computed tomography, permitting rapid surgical intervention.Our findings on computed tomography imaging assisted with the pre-operative diagnosis and enabled us to make a rapid surgical intervention. Early diagnosis may help preclude significant strangulation with unnecessary resection.
The Construction of Pairwise Additive Minimal BIB Designs with Asymptotic Results  [PDF]
Kazuki Matsubara, Sanpei Kageyama
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.514207
Abstract: An asymptotic existence of balanced incomplete block (BIB) designs and pairwise balanced designs (PBD) has been discussed in [1]-[3]. On the other hand, the existence of additive BIB designs and pairwise additive BIB designs with k = 2 and λ = 1 has been discussed with direct and recursive constructions in [4]-[8]. In this paper, an asymptotic existence of pairwise additive BIB designs is proved by use of Wilson’s theorem on PBD, and also for some and k the exact existence of l pairwise additive BIB designs with block size k and λ = 1 is discussed.
Fiscal Sustainability of Japanese Prefectural Government Debt  [PDF]
Rena Akamatsu, Kazuki Hiraga
Open Journal of Social Sciences (JSS) , 2015, DOI: 10.4236/jss.2015.38009
Abstract: This paper investigates whether the Japanese local government debt is sustainable. We apply the fiscal stabilization rule that each local government improves their primary balance in the current year when they issue additional debt the previous year. We check it using panel data of the Japanese prefectural governments. We find that Japanese prefectural governments were not sustainable across 1956-2007, though were sustainable across 1956-1989.
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