Yoshifumi Yamada

Alias-free image reconstruction using Fresnel transform in the phase-scrambling Fourier imaging technique

An image reconstruction technique that reduces aliasing artifacts by scalable image reconstruction in magnetic resonance imaging (MRI) is proposed. The signal obtained by the phase‐scrambling Fourier transform (PSFT) imaging technique can be transformed to the signal described in the Fresnel transform equation of the objects. Therefore, image reconstruction can be performed not only by inverse FT but also by inverse Fresnel transform. When a phase‐scrambling coefficient is given in a certain range, image reconstruction by inverse Fresnel transform allows shrinking of images over rather wide scales. Thus, reduced aliasing images can be reconstructed even from signals that produce serious aliasing artifacts by standard inverse FT reconstruction. Simulation and experimental studies reveal that the proposed method can be used to produce reduced aliasing images. Magn Reson Med 60:422–430, 2008.

NMR Fresnel transform imaging technique using a quadratic nonlinear field gradient

A new NMR imaging technique using a quadratic nonlinear field gradient is described. The center position of the nonlinear field gradient where the field intensity is minimum is moved spatially at a fixed amount in each imaging pulse sequence to produce nonlinear phase encoding as a function of position. A NMR image is reconstructed from the collected data by the computer data processing. The principle of this technique and many experimental results using a low field imaging system operating at 0.0192 T are presented. Theoretical and experimental comparison of the S/N of the image in this technique with that of the conventional Fourier imaging technique are made and the results show that both techniques have almost the same S/N. Moreover, the theoretical and experimental results show that this technique has a feasibility of a spatially localized imaging without using a conventional localization technique such as the use of the selective excitation in the presence of a linear field gradient.

Physiological control scheme of jaw simulator JSN/2A for improving reproducibility of open-close movement

In order to reproduce a life-like open-close movement in a robotized jaw simulator, JSN/2A, we provided it with a physiological and adaptive control scheme including antagonistic activities of posterior-temporalis and lateral-pterygoid actuators. This strategy was verified effective for improving horizontal stability of the movement.

Multiresolution image analysis using dual Fresnel transform pairs and application to medical image denoising

A new multiresolution image analysis and image processing technique which split the band in the Fresnel transform signal domain has been proposed. There are two methods to solve the Fresnel integral equation. Applying two different Fresnel transform methods in invert direction to an image sequentially with an adequate distance parameter, a down-scaled image can be produced representing a multiresolution image. In this paper, denoising of medical images are performed as an example of application to image processing. The results show that the proposed technique has advantages compared to the wavelet based method and adaptive nonlinear filtering.

Human Body Impedance for Contact Current Measurement in Japan

The radio-frequency protection guideline of Japan recommend the limits of contact current for contact hazard due to an ungrounded metallic object under an electromagnetic field in the frequency range from 10 kHz to 15 MHz. To arrange the standard measurement methods of contact current in Japan, the contact body impedance for the Japanese in the frequency range from 75kHz to 15MHz is obtained, and the simplified equivalent circuit is determined using nonlinear least squares method. In addition, the human body impedance is obtained from numerical simulation using the impedance method and voxel human model, and compared it with measured one.

Fast‐imaging method of plasma density spatial distribution by a microwave heterodyne interferometer

By using a microwave heterodyne interferometer assisted by microwave scattering techniques, computer tomographic images of spatial distributions of plasma density can be obtained. Two 9.5 GHz Gunn diodes, whose frequencies are offset by 35 MHz, are used in a heterodyne branch. In front of the detection horn antenna, multiple diodes are lined up, which scatter the microwave power with modulation frequency of 5 kHz, and the whole spatial information in one direction can be obtained by a pair of launcher‐detector systems assisted by these diodes. This system is a simple and low‐cost means to get images compared with popularly known multichannel interferometer techniques; still, precise, spatial resolution in the images has been observed.

On-line holographic reconstruction of NMR images by means of a liquid crystal spatial light modulator

A method of holographic reconstruction of nuclear magnetic resonance (NMR) images by making a hologram directly from the NMR signal is described. Since the signal obtained in NMR Fresnel transform technique is given by an equation similar to that of the Fresnel diffraction equation in light, it is possible to reconstruct NMR images by recording the NMR signal as a hologram and using a coherent optical system. We propose a new image reconstruction technique using a liquid crystal spatial light modulator for displaying holograms in a coherent optical system, which would realize a real-time reconstruction of NMR images. In the experiment, it is shown that good images were obtained by electrically displayed hologram.

Improvement of spatial resolution in magnetic resonance imaging using quadratic phase modulation

In the present paper, we propose a new magnetic resonance fast scan technique using the phase-scrambling Fourier transform imaging (PSFT), in which the strategy of data acquisition is similar to that of the standard Fourier imaging technique. The Fourier transformed image in the PSFT has a phase modulation in which the local spatial frequency is increased as the position moves away from the center of the image. Therefore, the signal length of the PSFT signal can be expanded using the restraint that the reconstructed image is a real-value object in the super-resolution algorithm. Simulation and experimental studies using a 0.0187T MR scanner were performed for the new improving image resolution method. It was shown that the spatial resolution could be improved in proportion to the distance from the center of the image by the quadratic phase modulation function, irrespective of the amount of noise, and the maximum resolution improvement is 2.0 times, as compared to the standard imaging method.

Image denoising using FREBAS multiresolution image analysis

This paper describes a 2-step image denoising technique based on the FREBAS transform that we have proposed as a new multiresolution image analysis. Noise removal is performed by applying a Wiener filter function, which is designed using a FREBAS prefiltered image, in the FREBAS transformed domain. Comparisons of image SNR improvement with previous single FREBAS denoising method and other methods such as nonlinear digital filter and Wiener filtering in the Wavelet domain were made. It was demonstrated that the proposed method provides the highest SNR improvement and the resultant image was free from serious image degradation.

Analysis methods of phase propagation in autonomic oscillation of Physarum polycephalum

A method for analysing the phase propagation in autonomic oscillation of Physarum polycephalum is described. Physarum polycephalum is often used for the study of autonomous distributed systems of natural organisms. When it moves coordinatively approaching to or from from the local stimulation, the propagation of the phase wave is observed in the surface. By analyzing spatial and temporal propagation of phase wave, we can find the rules of interaction between the oscillators. In this paper, which is about the analysis methods for the propagation of phase, the contour pattern of the analysis almost corresponds to that of the fundamental harmonic frequency series. Also, it is confirmed that Physarum polycephalum has the characteristic of a non-local connection. Phase propagation for repellent stimulation shows a discontinuity of phase which is not observed for attractant stimulation by using mutual information analysis.