Yoshiki Yamakoshi

Ultrasonic imaging of internal vibration of soft tissue under forced vibration

An imaging system that can display both the amplitude and phase maps of internal vibration in soft tissues for forced low-frequency vibration is described. In this method, low-frequency sinusoidal vibration of frequency under several hundred hertz is applied from the surface of the sample and the resulting movement in it is measured from the Doppler frequency shift of the simultaneously transmitted probe ultrasonic waves. Basic experiments are carried out by using 3.0-MHz ultrasonic waves. The two-dimensional maps of the amplitude and phase of internal vibration are shown, and the velocities of vibration are measured for some samples as well as in vivo.<<ETX>>

X-ray tomography for microstructural objects.

A high-resolution high-contrast x-ray tomography system for imaging the structure of submillimeter-sized objects is constructed. A precise data acquisition mechanism to realize a sharp pencil beam, use of an optimum x-ray band to achieve high contrast, deconvolution processing to restore blurred projections, and the iterative revision method to compensate for physically unavailable data are incorporated into the system. Basic experimental results obtained for an optical fiber used as a test object show that the system has ~20-mum. spatial resolution and good adsorption coefficient discrimination.

Transfer characteristic for a projection-type imaging system with an extended incoherent source

A new transfer characteristic is proposed for the analysis of projection-type imaging systems when the source is an extended incoherent one and the Fresnel approximation can be applied among source, object, and detector. This characteristic represents the propagation of the mutual power spectrum from the object plane to the detection plane and, once the imaging scheme is fixed, it can be derived uniquely regardless of the object’s structure. The image for given objects and the quality of the imaging system can be estimated from this characteristic. Numerical analyses to demonstrate the effectiveness of this method were carried out assuming a high-resolution x-ray imaging system.

Ultrasonic Phase Conjugator Using Micro Particle Suspended Cell and its Application

The phase conjugated wave for a given wave is defined as the wave which has the time-reversed wavefront of the original wave, hence it has many promising applications such as a real-time compensation of phase turbulence or an imaging without lens. To obtain the ultrasonic phase conjugated wave, several methods have been proposed.1,3 For instance, N.P. Andreeva et.al. proposed a method which is based on the use of small deformations of a liquid surface for the applied ultrasonic waves. This method, however, uses three waves simultaneously, that is signal, reference and phase conjugated waves, hence, the scattered waves of high intensity signal and reference waves are necessarily superposed as the extra noises over the desired weak phase conjugated waves. Moreover, the phase conjugated wave’s direction is fixed to the downward direction from the surface because the liquid surface is used. The later may give severe restriction when it is applied to practical system.

Linear restoration of projections obtained by an extended incoherent source

A new image-restoration method is proposed for a projection-type imaging system with an extended incoherent source. First, linearization of the system is carried out using the new transfer characteristic of the mutual power spectrum proposed earlier1; then the conventional linear restoration process is applied. Numerical analyses for a high-resolution x-ray imaging system are shown; these results demonstrate the effectiveness of this method.

Iterative image restoration from data available in multiple restricted regions.

The convergence properties of the iterative revision method for image restoration are examined when data are available only in restricted multiple regions. First, it is shown that this image restoration process is equivalent to solving a linear equation. Then a method of constructing an optimum observation system is shown that minimizes the mean-square error of the image obtained by stopping the iterative revisions at a finite number. Concrete optimum systems are derived for two cases, (i) when the sum of the widths of the restricted regions can be changed and (ii) when the sum of the widths of the restricted regions is fixed.

A Few Effective Signal Processings for Reflection-Type Imaging of Nonlinear Parameter N of Soft Tissues

The nonlinear parameter N (phase shift parameter) of a medium is considered to be related closely to the state of tissue at both levels of molecules and cells1),2),3),4). Hence, it is expected as one of the most significant promising new parameters for detection of disease such as cancer at their very early stages. As a concrete method the system which uses the pumping wave to give pressure variation and the probing ultrasonic waves to detect the resulting phase shift has been developed2).

X-ray lithography system: analysis and an optimum construction

An x-ray lithography system is analyzed by taking account of the partial coherence of the x-ray wave. The transfer characteristic proposed in an earlier paper [ J. Opt. Soc. Am. A1, 11 ( 1984)] is used in the evaluation. First, the simulated replication patterns obtained by using the method are compared with some experimental results. Then an optimum construction for an x-ray lithography system is discussed. It is concluded that, if the optimum ratio between the lateral spread of the x-ray source and the distance between the source and the mask is chosen, high-resolution patterns can be produced with minimum exposure time.

High-resolution x-ray lithography using a phase mask

A new high-resolution pattern replication method is proposed for an x-ray lithography system. To obtain high resolution, a phase mask is used which gives rise to the phase shift of nπ (n = 0 or 1) for the transmitted waves. This method gives high quality replication even where the conventional transmission–absorption type mask cannot be used effectively due to diffraction. The numerical results and a basic experiment carried out with laser light show the usefulness of this method.

Selection of the optimum wavelength for an x-ray tomography system

A means of selecting the optimum x-ray wavelength for an x-ray tomographic imaging system is proposed. In the evaluation, both the detection process and the image reconstruction algorithm are taken into account. The optimum wavelength is selected so that the stability of the reconstructed images is maximized. A concrete means of getting the optimum wavelength in connection with the detectable projections is also shown.