This paper proposes a new measurement method of the muscle stiffness, which corresponds to the diagnostic semi-quantitative stiffness based on the sensory information of the doctor, by using an ultrasonic vibrator, and describes basic characteristics of the measurement system. Distinct features of this method are as follows: (1) transcutaneous non-invasive quantitative measurement without pain and disconfort sensation, and (2) easy and less troublesome in operation for rapid measurement. These could be realized by the contact-impedance method which was based upon the fact that electrical impedance change reflected the stiffness of the tissue in the measurement by using an ultrasonic vibrator made of piezoelectric device. It was shown that the impedance locus of the ultrasonic vibrator varied with the stiffness of the object which was made contact with the vibrator tip. Measured values of the equivalent impedance were quantitatively discussed on the basis of the electrical impedance of a simplified electrical equivalent circuit, which corresponded to mechanical impedance of the objective material. The resonace frequency of this device was between 10 and 100kHz. It was considered that the frequencies used in the experiments were suitable for measuring biomechanical impedance of the muscle from the skin surface because there seemed to be no influence of the resonance of the living body structure and no necessity of complicated measuring system. Using the proposed system, the equivalent impedance could be measured easily under the condition that the depressed value of the vibrator tip was kept constant. From the experimental results, it was proved that the electrical equivalent impedance of the objective material had close relation to the stiffness obtained by palpation. Therefore it can be concluded that the obtained electrical equivalent impedance colud be considered as an index of the stiffness of the objective tissue.

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An efficient enhancement technique for bone fracture X-ray image is presented. In this technique a phase only synthesis is used, which is well known as a detector of an image's edge lines. The edge line image derived from the phase-only synthesis, which is also referred to here as the contour image, is very similar to the two-dimensional Laplacian image. When the observed image is not blurred, the usual two-dimensional Laplacian technique can be utilized in the process of image enhancement. In the case of medical X-ray images, however, the observed image is not always clear due to the scattering of the X-rays. For such a blurred image the Laplacian technique is not effective at image enhancement because the edge lines extracted by this technique are obscure. But, by using the phase only synthesis, we can often obtain very clear edge lines of the image even in such a blurred image. This factual result is owed to the property that the point spread function of the X-ray imaging system is well approximated by Gaussian-shape function. Gaussian-shape point spread function (PSF) is a zero phase function in its Fourier transform. Hence, the phase of the original image is not broken at all by the blurring with Gaussian-shape PSF. Thus, the phase only synthesis of the blurred image produces the very clear contour image. This means that a phase only synthesis can be well applied for an X-ray image enhancement. Furthermore when the phase only synthesis is applied to small sized sub-blocks which the image has been divided into, the more detailed edge lines of the image can also be detected. This is called sub-block phase only synthesis. In this paper using both full image and sub-block phase only syntheses, we develop a new effective X-ray image enhancement. The simulation results shows that the proposed technique is very effective for X-ray images.

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The relation between the actual arterial wall structure and its ultrasound image was discussed. A novel apparatus, which consists of a 20MHz ultrasound transducer and RF-signal acquisition system, have been designed to observe the longitudinal axis image of the isolated arterial wall. Isolated dog femoral arteries were used as the samples. The observed reflected ultrasound echo contained three unique echoes, which reflected at the external and internal surfaces and the external elastic lamina. The phase of echo which reflected at the external elastic lamina (boundary of media and adventitia) indicated that the acoustic impedance of the adventitia is lager than that of the media, which then suggested that the ultrasound velocity in the media and adventitia are different from each other because the acoustic impedance of these layers are different. The ultrasound velocity was calculated from the histological thickness, which was measured an optical microscope, and from the propagation time of ultrasound for those layers. The mean value and the standard deviation of velocity were 1663±85.2 (n=8) in the media and 2133±135.4m/s (n=8) in the adventitia.

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Electrical tinnitus suppressor, which was developed by the Hokkaido University, was implanted to 2 female tinnitus patients. A patient, 53 year old female, who suffered from chronic ear disease in her childhood. The other patient, 56 year old female, who had sensorineural deafness with unknown origin. This device was transformed from extracochlear implant which has been developed in the University. This device consists of a pair coils, one of which is implanted inside the temporal bone and the other is contained in a plastic case for hearing aids. The most effective conduction frequency was 30kHz and the most efficacious stimulus frequency for tinnitus relief was 10Hz. The maximum current for relieving tinnitus was set at 200μA. The heat emitting from both coils is so little at an intensity of 200μA that it does not hurt the body. Their hearing ability and emotion is improved in addition to complete tinnitus suppression following twice-a day stimulation at home using the device.

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In analysing ERP (event-related potential) by using the oddball paradigm, single trial recording of P300 (most important positive peak in the ERP) is strongly required, because the waveform of P300 may change at each trial depending on psychological and recording conditions of the subject. This study proposed a new method of single trial recording of P300 using second order model with time lags which represented a waveform of the P300. The model parameters of each waveform were determined so as to minimize the square sums of the modeling errors by using an optimization technique of the Fletcher-Powell method. The proposed method is superior to a conventional method of band pass filter especially when the frequency band of P300 and that of noise components are within the same range. Another advantage of the proposed method is that the feature of the P300 can be obtained directly in the model parameters. Effectiveness of the proposed method was proved in ERP data obtained from eleven normal subjects.

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