A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Localized fluid flow measurements with an He-Ne laser spectrometer

Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

/pdf/laser-doppler-speckle-and-related-techniques-for-blood-2tg3to9jwf.pdf

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

Photoplethysmography and its application in clinical physiological measurement

The development of optical methods in modern medicine in the areas of diagnostics, therapy, and surgery has stimulated the investigation of optical properties of various biological tissues, since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues. In this work, an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented. Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.

/pdf/optical-properties-of-skin-subcutaneous-and-muscle-tissues-a-wumm467r4a.pdf

Optical properties of skin, subcutaneous, and muscle tissues: a review

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.

Bio-speckle phenomena and their application to the evaluation of blood flow

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.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-9/issue-04/0000/Estimation-of-melanin-and-hemoglobin-in-skin-tissue-using-multiple/10.1117/1.1756918.pdf

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

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.

https://www.mdpi.com/1424-8220/13/6/7902/pdf

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

Disclosed is an ophthalomological diagnosis method and apparatus in which a blood vessel in the eye fundus is illuminated with a laser beam of a predetermined beam spot whose diameter is substantially equal to or smaller than that of the blood vessel in order to produce a speckle pattern which is produced by light scattered from the eye fundus. Boiling motion of the speckle pattern thus produced is then detected through a multiple detection aperture pattern comprised of a plurality of small apertures as fluctuation in a total amount of light passing through the small apertures to obtain a speckle signal which is evaluated to measure velocity of the blood flowing through the blood vessel concerned. This arrangement makes it possible to detect the speckle signal without any averaging process with an increase in intensity detected, thus enabling advantageous and successful measurement of the blood flow state in the eye fundus.

Ophthalmological diagnosis method and apparatus

In order to visualize human skin hemodynamics, we investigated a method that is specifically devel- oped 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 recon- structed 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. C 2011 Society of Photo-Optical Instrumentation Engineers

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-16/issue-8/086012/Noninvasive-imaging-of-human-skin-hemodynamics-using-a-digital-red/10.1117/1.3613929.pdf

Yoshihisa Aizu

Papers

Bio-speckle phenomena and their application to the evaluation of blood flow

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

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

Ophthalmological diagnosis method and apparatus

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