Yoshihisa Aizu

Bio-Speckle Phenomena and Their APPlication to the Evaluation of Blood Flow

Abstract The study of time-varying speckle phenomena observed in light-fields scattered from living objects is reviewed. The laser speckles produced from living objects may be called ‘bio-speckles’ and fluctuate temporally due to various physiological movements such as blood flow. The time-varying properties of the bio-speckles are experimentally investigated from the analyses of the power spectrum and the autocorrelation function. Based on the knowledge of dynamic bio-speckles, some methods are introduced for evaluating blood flow in the skin surface, internal organs, and ocular fundus. The experimental results show that the degree of blood flow is reflected sensitively by the time-varying properties of the bio-speckles and this can be utilized for monitoring the blood flow.

Estimation of melanin and hemoglobin in skin tissue using multiple regression analysis aided by Monte Carlo simulation

To estimate the concentrations of melanin and blood and the oxygen saturation in human skin tissue, we propose a method using a multiple regression analysis aided by a Monte Carlo simulation for diffuse reflectance spectra from the skin tissue. By using the absorbance spectrum as a response variable and the extinction coefficients of melanin, oxygenated hemoglobin, and deoxygenated hemoglobin as predictor variables, the multiple regression analysis gives regression coefficients. The concentrations of melanin and blood are determined from the regression coefficients using conversion vectors that are estimated numerically in advance, while the oxygen saturation is obtained directly from the regression coefficients. Numerical and experimental investigations were performed for layered skin tissue models and phantoms. Measurements of human skin were also carried out to monitor variations in the melanin and blood contents and oxygenation during cuff occlusion. The results confirmed the usefulness of the proposed method.

Evaluation of blood flow at ocular fundus by using laser speckle.

We report a method for noninvasively evaluating blood flow at the ocular fundus by using laser speckle phenomena. The intensity fluctuation of speckles scattered from a 1-mm-diameter illuminated area at the fundus is detected and analyzed by the photon-correlation technique, which gives us the relative degree of total blood flows within the probe area. The method is used to evaluate blood flows at the ocular fundus of a rabbit and normal human volunteers. The experimental results show that the present laser speckle method is useful for the relative evaluation of blood flows in the ocular fundus tissue.

Noninvasive imaging of human skin hemodynamics using a digital red-green-blue camera

In order to visualize human skin hemodynamics, we investigated a method that is specifically developed for the visualization of concentrations of oxygenated blood, deoxygenated blood, and melanin in skin tissue from digital RGB color images. Images of total blood concentration and oxygen saturation can also be reconstructed from the results of oxygenated and deoxygenated blood. Experiments using tissue-like agar gel phantoms demonstrated the ability of the developed method to quantitatively visualize the transition from an oxygenated blood to a deoxygenated blood in dermis. In vivo imaging of the chromophore concentrations and tissue oxygen saturation in the skin of the human hand are performed for 14 subjects during upper limb occlusion at 50 and 250 mm Hg. The response of the total blood concentration in the skin acquired by this method and forearm volume changes obtained from the conventional strain-gauge plethysmograph were comparable during the upper arm occlusion at pressures of both 50 and 250 mm Hg. The results presented in the present paper indicate the possibility of visualizing the hemodynamics of subsurface skin tissue.

Visualizing depth and thickness of a local blood region in skin tissue using diffuse reflectance images

A method is proposed for visualizing the depth and thickness distribution of a local blood region in skin tissue using diffuse reflectance images at three isosbestic wavelengths of hemoglobin: 420, 585, and 800 nm. Monte Carlo simulation of light transport specifies a relation among optical densities, depth, and thickness of the region under given concentrations of melanin in epidermis and blood in dermis. Experiments with tissue-like agar gel phantoms indicate that a simple circular blood region embedded in scattering media can be visualized with errors of 6% for the depth and 22% for the thickness to the given values. In-vivo measurements on human veins demonstrate that results from the proposed method agree within errors of 30 and 19% for the depth and thickness, respectively, with values obtained from the same veins by the conventional ultrasound technique. Numerical investigation with the Monte Carlo simulation of light transport in the skin tissue is also performed to discuss effects of deviation in scattering coefficients of skin tissue and absorption coefficients of the local blood region from the typical values of the results. The depth of the local blood region is over- or underestimated as the scattering coefficients of epidermis and dermis decrease or increase, respectively, while the thickness of the region agrees well with the given values below 1.2 mm. Decreases or increases of hematocrit value give over- or underestimation of the thickness, but they have almost no influence on the depth.

Estimation of Melanin and Hemoglobin Using Spectral Reflectance Images Reconstructed from a Digital RGB Image by the Wiener Estimation Method

A multi-spectral diffuse reflectance imaging method based on a single snap shot of Red-Green-Blue images acquired with the exposure time of 65 ms (15 fps) was investigated for estimating melanin concentration, blood concentration, and oxygen saturation in human skin tissue. The technique utilizes the Wiener estimation method to deduce spectral reflectance images instantaneously from an RGB image. Using the resultant absorbance spectrum as a response variable and the extinction coefficients of melanin, oxygenated hemoglobin and deoxygenated hemoglobin as predictor variables, multiple regression analysis provides regression coefficients. Concentrations of melanin and total blood are then determined from the regression coefficients using conversion vectors that are numerically deduced in advance by the Monte Carlo simulations for light transport in skin. Oxygen saturation is obtained directly from the regression coefficients. Experiments with a tissue-like agar gel phantom validated the method. In vivo experiments on fingers during upper limb occlusion demonstrated the ability of the method to evaluate physiological reactions of human skin.

Depth visualization of a local blood region in skin tissue by use of diffuse reflectance images

A simple method is proposed for visualizing the depth distribution of a local blood region in skin tissue by using diffuse reflectance images at two isosbestic wavelengths of hemoglobin, 420 and 585 nm. Monte Carlo simulation of light transport specifies a relation between optical densities and the depth of the region under given concentrations of melanin in the epidermis and blood in the dermis. Phantom and in vivo experiments were performed to show the usefulness of the method.

Measurements of flow velocity in a microscopic region using dynamic laser speckles based on the photon correlation

Abstract A method is studied for evaluating flow velocity in a microscopic region by means of the photon correlation measurements of dynamic laser speckles. Its principle is based on the autocorrelation measurements of dynamic speckles produced in the image plane by flowing objects. The method is used to evaluate the blood flow velocity in a 160-μm diam glass capillary. The experimental results show that a finite-size detecting aperture is useful for measuring effectively the photon correlation function of the lower light intensity in the shorter measuring time.

2 – Bio-speckles

Publisher Summary This chapter discusses bio-speckles. Laser light scattered from diffuse objects produces granular interference patterns, which are well known as “speckle phenomena.” If the diffuse object moves, the speckle grains also move and change their shape. The speckle pattern thus, becomes time dependent. This property can be applied to measurements of velocity, vibration, and displacement. The dynamic statistical properties of speckles have been extensively studied by theory and experiment, especially for velocity measurements. This chapter discusses the fundamental statistics of bio-speckles. They can be used for analyzing bio-speckle dynamics and extracting useful information from living objects. Bio-speckles show various aspects depending on the living objects to be measured, and methods of their analysis and applications can be changed accordingly. Thus, general theoretical approaches to analysis of bio-speckles seem to be considerably difficult. A promising way is to observe the bio-speckle fluctuations in detail and to establish experimentally and empirically the relation between the fluctuations and the necessary information to be extracted. The field of bio-speckle techniques covers all the subjects of speckles obtained from various living objects: (1) short- and long-range temporal fluctuations, (2) spatial fluctuations, (3) intensity and phase fluctuations, (4) their statistical properties and fundamental modeling, and (5) applications, including the design of measuring apparatus. The field can also be combined with conventional speckle metrology, such as speckle photography and speckle interferometry.

Bio-speckle flowmetry for retinal blood flow diagnostics

Bio-speckle flowmetry for measuring the retinal blood flow velocity is described. The measuring principle is briefly discussed in comparison with the laser Doppler method. The basic properties of the photon correlation measurements including reproducibility were experimentally investigated with a rotating ground glass disk and for the normal human retina. The error was estimated to be less than 20% for in vivo measurements. By using a glass capillary model, the reciprocal of correlation time was calibrated to the mean flow velocity with a consideration of the effects of the vessel diameter and the background reflectance. The blood flow volume rate in the human retina was estimated by using the calibrated velocity and the vessel diameter. The results compared well with those reported in the literature, and show the usefulness of this flowmetry for clinical diagnostic purposes.