Naomichi Yokoi

Estimation of particle trajectory effects and their reduction using polarization in phase Doppler particle measurements

Phase Doppler methods that measure the diameter of moving spherical particles are sensitive to particle trajectory effects that cause a phase error under Gaussian beam illumination. This error results from the interference between reflected and refracted rays from the particle. We first numerically estimate the particle trajectory effect using the geometrical optics approximation and the generalized Lorenz-Mie theory (GLMT) and, then, discuss the optimum measurement conditions that minimize the phase error. We next theoretically and experimentally investigate a method for reducing the trajectory effect using the separation of reflected and refracted rays on the basis of the polarization change. Experimental results show the usefulness of this method.

Unidirectional phase-Doppler method for particle-size measurements

We propose what we believe to be a novel unidirectional phase-Doppler method for sizing moving spherical particles on the basis of the phase difference of two polarized Doppler beat signals in a single scattering direction. Light scattered by a moving particle is divided into two rays, which are detected with different polarization angles to transmit dominantly reflected or refracted rays. The phase difference between two signals is linearly proportional to the particle diameter with a given particle refractive index and geometrical parameters of the optical system. To explore the optimum polarization condition, we numerically investigated the phase-diameter properties in relation to polarization angles by using the geometrical optics approximation and generalized Lorenz-Mie theory. We also performed experiments with polystyrene and glass particles to verify the usefulness of the proposed method.

Simultaneous imaging of blood flow and hemoglobin concentration change in skin tissue using NIR speckle patterns

We propose a method for imaging simultaneously blood flow and hemoglobin concentration change in skin tissue using speckle patterns acquired at two wavelengths of 780 and 830 nm. Experimental results demonstrate that the method is useful for time-varying analysis of blood circulation in human forearm skin tissue from one set of sequential speckle images.

Improvement of temporal resolution in blood concentration imaging using NIR speckle patterns

In the imaging of blood concentration change using near infrared bio-speckles, temporal averaging of speckle images is necessary for speckle reduction. To improve the temporal resolution in blood concentration imaging, use of spatial averaging is investigated to measured data in rat experiments. Results show that three frames in temporal averaging with (2×2) pixels in spatial averaging can be accepted to obtain the temporal resolution of ten concentration images per second.

Novel phase Doppler method for particle size measurements using a single directional polarized detection

A novel phase Doppler method is proposed for sizing of moving spherical particles on the basis of the phase difference of two polarized beat signals in a single scattering direction. Light scattered by a moving particle is divided into two rays that are detected with different polarization angles to transmit dominantly reflected or refracted rays. The phase difference between two signals is linearly proportional to the particle diameter with a given refractive index. Numerical computations and experiments were performed to verify the usefulness of the proposed method.

Measurements of blood flow and hemoglobin concentration change in anesthetized rat using two-wavelength laser speckle imaging

We measured simultaneously blood flow and hemoglobin concentration change in the exposed area of an anesthetized rat using laser speckle patterns acquired at two wavelengths. Blood flow was successfully analyzed in a frame rate. Changes of oxy- and deoxy-hemoglobin concentrations were temporally measured. These results indicate the usefulness of the method.

Speckle imaging of moving objects hidden by turbid media using low-coherence interferometry

We propose a method for depth-resolved imaging and relative-velocity sensing of moving objects hidden by turbid media using low-coherence interferometry combined with the speckle subtraction. Experimental results show that the method is useful for imaging objects hidden by the Intralipid or a diffuse plate in a depth-resolved manner and estimating the relative velocity.

Color appearance of skin tissues and blood vessels: in-vitro and in-vivo experiments

The bluish appearance of veins in the skin tissue was experimentally investigated by in vivo and in vitro measurements. The color of skin surface including veins inside was evaluated by spectrophotometry and color analysis in the CIEXYZ and CIELAB colorimetric systems. The bluish appearance was successfully interpreted by the dominant wavelength and the color difference. Results for in vitro experiments showed that the degree of bluish appearance depends on the depth and diameter of blood vessels.

Investigation of temporal response in finger blood flow and concentration change in occlusion test on human arm using bio-speckle patterns

We have developed so far the method for imaging simultaneously blood flow and blood concentration change in skin tissue by using two-wavelength near infrared laser speckle patterns. We conducted experiments for human volunteers to confirm the feasibility of the method for estimating temporal response in the blood flow and blood concentration change in a human finger to occlusion on a human arm with different pressures from 50 to 150 mmHg. The results demonstrated that the response may depend on individual minimum and maximum blood pressure values.

Fractality of biospeckle pattern observed in blood coagulation process

It has been known that speckle images observed for living bodies illuminated by laser light sometimes show fractal appearances. This has been utilized, for example, for tomographic imaging of the porcine arterial tissue. Fractality can also be seen in speckle images generated by the blood in the process of coagulation. A fractal dimension (FD) of the speckle image is, thus, expected to be a global marker of haemostasis, arteriosclerosis, and so on. In the present study, we experimentally investigate fractality of biospeckle pattern observed in coagulation process of horse blood.