Magnetoencephalography (MEG) was recorded under attend and ignore conditions to detect auditory steady-state responses (ASSR) to stimuli regularly repeated 40 times/s for 2 s, and synchronization of its 40-Hz component was measured using phase coherence. The major finding of the experiment was that the increased ASSR obtained by averaging in the attend condition was due to the increased degree of synchronization as the result of stimulation during the 40-Hz activity rather than the increase in power. We made a simple differential equation model for phase dynamics and compared the change of phase coherence calculated from the model with that obtained from the measurement. The model predicted the behavior of experimental phase coherence quite well, and the estimated value of one of the two parameters in the model representing the effect of stimulus on the phase was significantly larger for the attend condition than for the ignore condition, suggesting the validity of the model.

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This is a basic study on evaluations of gastrointestinal motility and autonomic nervous activity, diagnosis of diseases, and examination of effects of medical treatments using electrogastrography (EGG). Using time series analysis, we analyzed temporal variations in the EGGs of healthy young women during sleep and extracted the characteristics of variations. The subjects were healthy women between 18 and 22 years old. Using portable equipment, electrogastrographies at 4 points an the abdominal surface were recorded with the monopolar lead for five hours from the beginning of the sleep. The EGGs were recorded at a sampling frequency of 1 Hz. We calculated cross-correlation functions for all combinations of electrogastrographies recorded at different measuring points. Moreover, frequency characteristics of each EGG were derived from the power spectra estimated by Auto-Regressive models. Every 10 minutes, we specified a dominant frequency and the integrated powers of the frequency band at around 3-cpm (3-cpm band), because the pacemaker for stomach electric activities is around 3-cpm (0.05 Hz). We obtained low contribution rates for electrogastrographies in all combinations of different measuring points and could show that time series of electrogastrographies were independent of each other. As for the power spectra obtained at the 4 electrodes, the dominant frequencies in the 3-cpm band of the point around the fundus were higher than there obtained at other points. In this paper, “Active ratio” was proposed as an index to evaluate the gastrointestinal motility. Temporal variations of this index showed that gastrointestinal motility was considered to be active during the entire sleeping period. Moreover, the difference in the autonomic nervous activity between the first and second halves of their sleeping periods or the effects of circadian rhythm could be evaluated by the power spectra.

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We applied a newly developed high-speed ultrasonic gas sensor to a respiratory monitoring system. This sensor was developed based on the principle of amplitude attenuation described by gas kinetic theory in a gas medium. Since the sensor measures mean molecular mass without using a chemical reaction (i.e., using ultrasonic amplitude, a physical property), high-speed data acquisition has been realized for monitoring the respiratory gas-change process. Although the measurement of CO₂ in respiratory gases using an infrared absorption detector has already been established as a standard monitoring technique, the detectors are bulky and the fastest sampling rate is 100 kHz. at best. The newly developed respiratory gas-monitoring sensor is small and can obtain respiratory data at a sampling rate of over 1 kHz. We compared our proposed ultrasonic gas sensor with a commercial infrared respiratory sensor (Nihon Koden: TG-920P), and found that newly developed sensor can detect temporal changes in concentrations of CO₂ and H₂O with much better fidelity than the commercial respiratory sensor.

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The study of visual illusion is an important method for clarifying the mechanism of visual perception. However, many details about the cause of visual illusions are still unknown. In this study, based on the physiological characteristics of the retina, we propose an on-center receptive field model of the retina. Using this model, we simulate the distributions of the inducing fields for some visual stimuli. We then prove the validity of our proposed model by comparing these results with those from previous studies. Furthermore, we simulate the distributions of the inducing fields for some typical visual illusions. The results clearly explain the visual illusion phenomena rationally. Based on the results, we suggeste that some visual illusions are likely caused by distributions of the inducing field in the retina, which themselves are induced by the visual illusions. The practicality of the proposed model is also verified.

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The purpose of this study is to investigate the optical absorbance spectrum of bone tissue in the near-infrared region for the development of bone densitometry using near-infrared light. Using bone samples from a bovine femur, optical absorbance spectrums were measured between 750∼2500 nm. With high bone density, the absorbance increased beyond 1400 nm. To predict bone density from the spectrum data, pairs of wavelengths with absorbance ratios or differences having a high correlation coefficient (r>0.99) with bone density were identified. One of the best results was shown by a pair of 1200 nm and 1550 nm with coefficients(r) of 0.994 and 0.996 for absorbance ratio and difference, respectively. Even in thedensity range of the trabecular bone, the coefficients were 0.892 and 0.881 for absorbance ratio and difference, respectively. The results suggest the possibility applying near-infrared spectroscopy to bone densitometry.

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We developed a passive dorsiflexion and plantar flexion device for ankle joints in standing posture using a lever crank mechanism. We confirmed that dynamically stretching the triceps surae improves the blood flow via muscle pumping effect. This demonstrates that the system is effective for preventing venous thrombosis and articular contraction. The flexibility of the ankle joint is evaluated by the dorsiflexion energy, which is estimated by integrating the ankle joint torque with respect to dorsiflexion angle. The variation of flexibility caused by stretching is quantitatively traceable and estimable. Furthermore, balancing capability can be simultaneously evaluated by the magnitude of variation of the ankle joint torque while maintaining a standing posture against the change in the ankle joint angle.

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Locally sustained forces are the main cause for the onset of pressure ulcers. Therefore, it is important to reduce and redistribute these forces using antidecubitus cushions. In this study, we constructed a three-dimensional buttock model incorporating two bones (ischial tuberosity, a site prone to the development of pressure ulcers, and femur) covered by soft tissue. Using the model, we evaluated cushions that can effectively distribute seat-interface pressure (SIP) and von Mises stress in subcutaneous tissue (SiST). To examine the differences of force distribution capability in four materials (soft and hard gels/foams) and three thicknesses (10, 30 and 50 mm), we simulated sitting single-layer cushions. The results showed that SIP and SiST decreased as the thickness of the cushion increased. In addition, to determine whether a two-layer cushion can distribute force more effectively than a single-layer cushion, we combined two of the materials (thickness of each material: 25 mm) to form a 50-mm-thick two-layer cushion. The results showed that when foam was placed under the gel, the SIP and SiST values were smaller than those for a single-layer cushion. Results of previous studies have indicated a three-material two-layer cushion, in which the softest material of the three materials is placed under the ischial tuberosity region—where high contact forces develop—and is surrounded by the hardest material to support the remainder of the pelvic structure, has the best force distribution efficiency. Therefore, we made a three-material two-layer cushion, placing the softest material under the ischial tuberosity region. The results indicated that SIP was similar to that of the two-layer cushion, but SiST was the smallest in this simulation. From these results, we conclude that forces can be distributed efficiently in a three-material cushion by placing the softest material under the ischial tuberosity region.

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The depression of peripheral vessels due to aging can causes serious diseases as well as the destruction of small organs and gangrene. Our research activity is now directed at dynamic observation of peripheral vessels using optical coherence tomography (OCT) for the purpose of developing a new technique for screening or the diagnosis of aging vessels. In this paper, the description is focused on OCT imaging of arterioles of the human finger. Clear imaging of arterioles at a depth of 1 mm or more is attained with an image resolution of around 15 μm using the light-focusing effect of an objective. So-called dynamic OCT was developed using the all-optical-fiber interferometer optics to obtain the OCT images of an arteriole at the frame interval of 5 sec. Expansion and contraction of the cross-section of the arteriole are observed clearly in the time-sequential OCT images. Such elastic motion of the arteriole is almost independent of heartbeat. It is concluded on the basis of our experimental results that an arteriole remarkably expands and contracts in response to physiological functions of the arteriole as controlled by sympathetic nerves.

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We evaluated the stress distribution in a cylindrical model and a shape model obtained from human heart using two different fiber orientations. For both orientation models, the results showed large differences between the stress distribution in the cylindrical model and the measurement-based shape model. These results suggest that stress distribution is highly dependent on the model geometry, and the usage of a measurement-based shape model is important for evaluating left ventricular (LV) wall stress distribution. This fact may have some influence on the reported homogeneity of stress distribution in an anatomical fiber orientation model that uses a mathematical symmetric shape model.

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This study propose an algorithm for estimating walking patterns by the use of foot-pressure sensors embedded in shoes. The algorithm can classify each step into seven patterns: standing, level walking, walking downstairs, walking upstairs, walking downhill, walking uphill and running. The classification is based on foot contact duration, maximum foot pressure upon impact, maximum foot pressure upon lifting foot, maximum pressure at the forepart of the foot upon foot impact and maximum foot pressure at the toe upon lifting foot. To examine the algorithm, the foot pressure of eight healthy male subjects was measured while walking on a level floor, up stairs and down stairs. Experimental results showed that the estimated accuracy of walking patterns was over 94%. The estimated accuracy of the number of steps based on the foot pressure was 100%, while that of the pedometer on the market was 85 to 94%.

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Muscles not only have a contractile function, but also a viscous elastic property. This property is observed in response to stretching the contracting muscle. The purpose of this study is to investigate the relationship between stretch-evoked torque and the conditions before stretching (contraction level, velocity and length) the flexor pollisis longus muscle (FPL). The subjects sat on a chair, and their left hands were affixed to the apparatus. Then, they were instructed to track the target force of FPL displayed on the monitor, and to keep isotonic contraction (7 to 35% of the maximum voluntary contraction (MVC) by slowly stretching at an angular velocity V₁ (3 to 13 deg/s). After 2 s, a small ramp stretch (300 deg/s) was applied to the thumb from various angles (7 to 27 deg). The angle, flexing torque of the thumb, and electromyogram (EMG) of the FPL were measured. In the same way, the passive torque was measured in response to the length perturbation at a resting state. Each measurement was carried out ten times. The stretch-evoked torque was estimated by subtracting the passive torque and isotonic torque from the observed torque. As a result, the stretch-evoked torque increased as the contraction level and angular velocity (V₁) increased, but the stretch-evoked torque decreased as the length of the FPL increased. In conclusion, it was shown that the viscoelastic property of the muscle changed not only in accordance with the muscle activation level, but also in accordance with velocity (V₁).

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The ability to travel is important for disabled persons because it enables them to participate in social activities. Even though there is a wide range of technologies for supporting the visually impaired to travel, many of the technologies are under utilized. Part of the explanation lies in the behavioral patterns of many visually impaired who venture outdoors very little. To encourage travel, we have developed a system that selects travel routes suitable for visually impaired travelers. The algorithm uses an analytic hierarchy process (AHP)-one of many decision-making mathematical models-together with a digital map. The preferred or favored amenities of the traveler are reflected quantitatively in the travel route selection. Therefore, it is important to prepare the appropriate travel routes before making use of the system. In this paper, we asked 10 people with normal vision to quantitatively evaluate the preset travel routes automatically presumed by the system. As a result, it was verified that several travel routes prepared by our system were available for 70% of the users. Finally, we had two visually impaired people qualitatively evaluate the system from the user's viewpoint.

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Minimally invasive endoscopic fetal surgery enables intrauterine intervention with smaller risk to the mother and fetus. We designed and fabricated a prototype of a fetus-supporting manipulator equipped with flexible bending/curving mechanisms and a soft balloon-based stabilizer to prevent the fetus from free-floating during endoscopic intrauterine surgery. The manipulator enables the stabilizer to reach the target sites within the uterus under ultrasound guidance. The balloon-based stabilizer can be inserted into the uterus from a small incision. The experiments using a fetus model show that the manipulator is well controlled using ultrasound guidance, and its curving mechanism and balloon-based stabilizer are clearly visible when implementing fetus support.

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In order to elucidate the process of morphological formation in the development of human embryos, it is useful to browse their three-dimensional (3D) images. Currently, we are trying to acquire sets of 2D images from a large number of serially sectioned human embryo specimens and reconstruct 3D images from the series of images. Since the specimens have been obtained over a period of time, the 3D reconstruction has to be carried out retrospectively. Problems of image acquisition for retrospective 3D reconstruction include a large amount of manual operation, damage to some sections and variations of orientation. The goal of our research is the efficient acquisition of 2D images. We propose semi-automated methods to acquire images, with the elimination of damaged sections and rearrangement of the series of specimens. From experiments, we have evaluated the effectiveness of our proposed methods.

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In the medical field, three-dimensional (3D) digital images are commonly used with recent advances of imaging techniques such as magnetic resonance imaging (MRI) and X-ray computed tomography. In most cases, objects are visualized in 3D shapes by surface rendering or volume rendering using the information of isosurfaces. However, objects of interest are frequently occluded by other objects or by themselves. Volume clipping is a common technique to reduce the occurrence of occlusion, but the procedure is difficult to apply for complicated shapes. The Region-based Contour Tree (RBCT) describes a structure of isosurfaces in digital images as a tree structure. Using RBCT, we can extract a region surrounded by a single isosurface, and the extracted region is not occluded by other regions. Nevertheless, self-occlusion cannot be eliminated. In order to eliminate self-occlusion, we propose a method to divide isosurfaces using RBCT. We introduce a “region-dividing plane” that divides a region into two parts: the part of interest and remainder, which is hidden by self-occlusion. Using RBCT interactively combined with the region-dividing, we can efficiently extract regions of interest from a 3D image without self-occlusion even if the shapes of regions are complicated.

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A morphological database of human embryos is a valuable data resource to elucidate morphological formation during the embryonal development of humans. In this report, we describe a system constructed to retrieve and present from a database including a large quantity of three-dimensional (3D) magnetic resonance (MR) microscope images acquired from embryo specimens. The database consists of the 3D images, external photographs and bibliographical texts, and the system retrieves and displays the information of the database via a network. The system enables users to retrieve bilingual (Japanese and English) data, observe sections of 3D images, and view 3D isosurfaces of the specimens extracted from the 3D images. In the procedure of viewing 3D isosurfaces, morphological features of the specimens can be compared.

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Transcranial magnetic stimulation (TMS) is a method for noninvasive stimulation of cerebral cortex, and it has contributed to clinical and basic researches of brain function. In order to estimate the accurate stimulating points of the cortex in TMS, precise measurement of the subject's head and the stimulating coil is necessary. In this study, we have developed the positioning TMS system with a three-dimensional (3-D) digitizer and a multi-articular system. We proposed a method for the accurate measurement of a subject's head and cortex, in which the location data of the subject's face surface captured by a 3-D digitizer were superimposed on the magnetic resonance imaging (MRI) data of the subject's face surface. Using this system, the precise estimation of the stimulated sites of the cortex in TMS was achieved. The validity of the system was verified by the experiment on the TMS of the motor cortex.

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The objective of this study was to propose a new population pharmacokinetic analysis method that is applicable for groups where the distribution of each parameter is a normal mixture. In this study, using the extended least squares (ELS) technique, which is one of the population pharmacokinetic analysis methods, population pharmacokinetic parameters were estimated for plasma concentrations observed from many people. This method was composed of two steps. First, a set of population pharmacokinetic parameters with varying initial values was estimated. Second, the set of estimated parameters was classified using non-hierarchical cluster analysis, and then the representative value of each cluster was calculated. The representative values that were closest to the known pharmacokinetic values were judged to be the population pharmacokinetic parameters of the group where each parameter was a normal mixture distribution. In order to show the usefulness of the present method, simulation experiments were conducted. The dataset of plasma venlafaxine concentration from 100 subjects was created based on published reports. The 100 subjects were classified into the two genotypes; 50 subjects were CY P2D6 ^*1/^*10, and 50 subjects were CY P2D6 ^*10/^*10. The distributions of the pharmacokinetic parameters were bi-modal. Simulation results were only slightly different from the pharmacokinetic parameter distributions of the dataset, proving the usefulness of the method presented.

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Our previous computer simulation study showed that the fuzzy controller based on cycle-to-cycle control would be useful in controlling the swing phase of hemiplegic gate using functional electrical stimulation (FES). However, a simplified musculoskeletal model of a swing leg with the floor reaction force eliminated was used in the previous study. In this paper, a musculoskeletal model consisting of the stance and swing legs with a floor model was developed first. Then, the fuzzy controller for controlling the swing phase was examined using computer simulation of the developed model including the toe off and initial contact. Computer simulation results showed that the fuzzy controller and the stimulation schedule developed in our previous work were adequate, and that modifying the schedule considering the strength of the plantar flexion of the ankle joint would be more effective for improving responses at an early stage of control. A control method based on using electromyograms (EMGs) was also discussed. The fuzzy controller and a previously created EMG-based stimulation schedule, which was unable to control the swing phase, were modified by changing the role of the rectus femoris muscle. The modified fuzzy controller with a new EMG-based stimulation schedule was found to develop the swing phase movement appropriately.

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We measured the MEG signals from seven normal, right-handed Japanese subjects during visual categorization tasks for word stimuli, and analyzed 5-15 Hz frequency components using time-frequency analysis. The power spectra normalized by mean powers during 0.5s before the onset of stimulation, indicated attenuations in the temporal and parietal regions of both hemispheres and in the occipital region at a latency of 0.5s and later. The attenuation in the right parietal region was due to left finger movement in response to the task, and the attenuation in the left temporal region was related to categorization and response. These results indicate that the neuromagnetic activities that the time-domain analysis cannot visualize from the event-related responses are observed using time-frequency analysis.

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The auto-fluorescence characteristics of human teeth change with age. AGEs (advanced glycation endproducts), which are a crosslink of collagen, are considered to be involved in the mechanisms that cause the fluorescence characteristics to change. Although fluorescence intensity is a well-examined index of aging, it has inherent limitations. In contrast, fluorescence lifetime is useful for the evaluation because it can be reviewed quantitatively. Therefore, we mapped the distribution of fluorescence lifetime of teeth in relation to the formation and aging of teeth. The fluorescence decay profile of teeth was measured by time-correlated single photon counting, and lifetime was calculated from the fitting curve of the decay profile in a two-component exponential function. As a result, the distribution of fluorescent lifetime in dentin corresponded to tooth development; fluorescent lifetime of the crown dentin was shorter than that of the root dentin. Furthermore, the fluorescence lifetime decreased as human age increased. Because these changes in fluorescent lifetime are attributed to the accumulation of AGEs, whose fluorescence lifetime is short, our mapping of fluorescent life visualizes the formation and aging of teeth.

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Several methods for monitoring the respiratory status of small experimental animals are available; however, most of them are invasive and are not suitable for use with free-moving animals. A 3-dimensional (3D) motion capturing method is widely used for monitoring and analyzing the motion of moving objects. In this study, we examined whether or not this method is capable of monitoring the respiratory status of small animals and explored the potential use for less invasive monitoring method for the free-moving small animals. 21 markers that reflect near-infrared (NIR) light were attached to the skin of the trunk of an anesthetized rat. The body movement synchronized with spontaneous respiration was detected using eight NIR video-cameras that emitted a weak NIR light and captured the reflected NIR light from the markers. The respiratory status was analyzed by calculating the change in volume of a virtual polyhedron, for which the attached makers were regarded as vertexes. The 3D motion capturing system detected the chest movement with a spatial resolution of 0.26 mm and a time resolution of 4 msec. Volumetric analysis of the virtual polyhedron provided the respiratory rate, allowing monitoring of respiratory fluctuation induced by hypoxia. This study demonstrates that a 3D motion capturing system can be used as a noninvasive monitoring method for checking the respiratory status of small animals.

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Attempts have been made to apply advanced CAD/CAM technology to the design and manufacturing of dental prostheses such as crowns and bridges in order to simplify production procedure as well as to improve their quality. Presently, several dental CAD/CAM systems capable of designing occlusal surface are available commercially. Design of complicated occlusal surfaces is of primary importance in dental CAD, due to its function in patient's stomatognathic system. In particular, location of contact points in the intercuspal position is essential to obtain a functional occlusal surface without interference. Previous interfere-free design, however, has been done on a trial-and-error basis by using visual inspection. In order to improve such time-consuming and inaccurate procedure into a semi-automatic and accurate one based on quantitative evaluations, we already developed two difference functions for dental CAD system such as 1) a virtual dental articulator, and 2) proximity mapping on the crown surface relative to its opposing occlusal surface. Subsequently, this paper proposes a computer-aided system for assisting the determination of occlusal contact points employing the proximity mapping on the opposing surface. The system can designate such regions, which can be estimated from contour of the opposing occlusal surfaces and their relative movements simulated by using the virtual articulator. In an attempt to evaluate applicability of our system, several experiments for designing the crown of a lower first molar were carried out using three different types of opposing teeth with different cusp angles. The results demonstrated that all contact points located within the designated regions completely satisfied the required conditions regarding contact and separation during every tooth excursion. It is strongly suggesting that our assisting system has wide range of clinical applicability.

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Focusing on the application of linearly-constrained adaptive beamformer techniques to fMRI-MEG integrative analysis, we have examined an approach which determines the center of gravity in each fMRI activated cluster as the location of the linear constraints. First, we simulated MEG data generated from two sources distributed in circular forms placed at visual areas V2 and V5, which are temporally strongly correlated. Two fMRI activated clusters are assumed to cover the two sources. The linear constraints for the voxels in a cluster are defined to suppress the power from the source at the center of gravity of the other cluster. The spatial distributions and the time courses of the two correlated sources at V2 and V5 are successfully reconstructed. We applied the approach to data obtained during an apparent motion perception task and were able to confirm its availability. These results demonstrate that the proposed approach based on linearly-constrained adaptive beamformer techniques is promising as an fMRI-MEG integrative analysis.

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For robotic surgery assistance systems that use magnetic resonance imaging (MRI) for guidance, the problem of electromagnetic interference is common. Image quality is particularly degraded if motors are running during scanning. We propose a novel MRI-compatible method considering the pulse sequence of imaging. Motors are driven for a short time when the MRI system stops signal acquisition (i.e., awaiting relaxation of the proton), so the image does not contain noise from the actuators. The MRI system and motor are synchronized using a radio frequency pulse signal (8.5 MHz) as the trigger, which is acquired via a special antenna mounted near the scanner. This method can be widely applied because it only receives part of the scanning signal and neither hardware nor software of the MRI system needs to be changed. As a feasibility evaluation test, we compared the images and signal-to-noise ratios between the cases with and without this method, under the condition that a piezoelectric motor was driven during scanning as a noise source, which was generally used as a MRI-compatible actuator. The results showed no deterioration in image quality and the benefit of the new method even though the choice of available scanning sequences is limited.

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Improvements in magnetic resonance imaging (MRI) technology have made it possible to measure diffusion of the water molecule, which was difficult to measure in the past. The degree of water diffusion can be obtained from the intensities of diffusion-sensitive MR images (diffusion-weighted image: DWIs). Using DWIs with six dimensions, calculation of the diffusion tensor becomes possible. In this research, we measure the diffusion tensor image (DTI) using a MR microscope (MRM-DTI) with a spatial-resolution of the 100-micron order. A motion-proving magnetic field gradient (MPG) is used in the MRM-DTI. There exists a problem, however, that the result is not uniform according to the direction of the MPG regardless of the uniform phantom due to the coil and power characteristics. Here, we propose a new method of b-value calibration using the isotropic region included in the anisotropic phantom. Using this calibration method, we tried to measure the DTI not only for an isotropic phantom, but also for an anisotropic phantom.

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In clinical rehabilitation, the Timed Up-and-Go Test (TUG-T) is known as a simple technique for evaluating basic activities, especially the risk of falling. Usually, the time of TUG-T is counted, and the correlation between falling phenomenon and time of TUG is relatively high. We have been examining a quantitative evaluation method of the activity using the signal of an accelerometer attached to the lumbar position. However, it is difficult to specify the activities phase clearly from the signal obtained by the accelerometer. Thus, in this study, we propose a combination of accelerometer and rate gyro-sensor to specify the activity phase of TUG-T. For the comparison, trained therapists measured the time for each activity phase using VTR images. As a result, proposed classifications of activity phase well correlated to the observations made by the therapists. In the use of both accelerometer and the gyro-sensor signals, it was possible for the activity phase to make detections similar to those of therapists' observations.

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Small animals like mice or rats are widely used for cardiovascular research and development. The development of cardiovascular drugs requires that electrophysiological studies be conducted using such small animals. Magnetocardiography (MCG) for small animals has not been established yet. In the present study, a newly developed micro-magnetometer array and, 9-channel superconducting quantum interference device (SQUID) with a 2.5-mm diameter pickup-coil were used for MCG measurements. A cryoinjury probe was used to produce regional myocardial injury in mouse and rat hearts, and the specific MCG patterns corresponding to injured locations were recorded with the micro-magnetometer array/SQUID combination. QT prolongation induced by quinidine (60 mg/kg) in mice and rats was recorded. In mice and rats, anterior myocardial injury created a QS pattern. Posterior myocardial injury deepened the depth of the S wave. Thus, the micro-magnetometer array/SQUID combination enabled the in vivo localization of injured myocardium in small animals. Quinidine-induced QT prolongation was successfully measured by MCG. The newly developed miniature magnetometer array system for MCG facilitates the research process of electrophysiological studies of small rodents.

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