Localized fluid flow measurements with an He-Ne laser spectrometer

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.

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

A survey of the literature is presented that provides an analysis of the optical properties of human skin, with particular regard to their applications in medicine. Included is a description of the primary interactions of light with skin and how these are commonly estimated using radiative transfer theory (RTT). This is followed by analysis of measured RTT coefficients available in the literature. Orders of magnitude differences are found within published absorption and reduced-scattering coefficients. Causes for these discrepancies are discussed in detail, including contrasts between data acquired in vitro and in vivo. An analysis of the phase functions applied in skin optics, along with the remaining optical coefficients (anisotropy factors and refractive indices) is also included. The survey concludes that further work in the field is necessary to establish a definitive range of realistic coefficients for clinically normal skin.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-17/issue-9/090901/Optical-properties-of-human-skin/10.1117/1.JBO.17.9.090901.pdf

Optical properties of human skin.

A thorough understanding of optical properties of biological tissues is critical to effective treatment planning for therapies such as photodynamic therapy (PDT). In the last two decades, new technologies, such as broadband diffuse spectroscopy, have been developed to obtain in vivo data in humans that was not possible before. We found that the in vivo optical properties generally vary in the ranges μ(a) = 0.03-1.6 cm⁻¹ and μ'(s) = 1.2-40 cm⁻¹, although the actual range is tissue-type dependent. We have also examined the overall trend of the absorption spectra (for μ(a) and μ'(s)) as a function of wavelength within a 95% confidence interval for various tissues in vivo. The impact of optical properties on light fluence rate is also discussed for various light application geometries including superficial, interstitial, and within a cavity.

/pdf/a-review-of-in-vivo-optical-properties-of-human-tissues-and-4sa3qlende.pdf

A review of in-vivo optical properties of human tissues and its impact on PDT

Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of in-vivo skin in the wavelength range from 650 to 1000nm using the diffusing probe in the “modified two-layer geometry”. In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000nm. It was found that the concentration of chromophores, such as oxy-hemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer’s size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy- and deoxy-hemoglobin as assessed at wavelengths above and below 600nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.

/pdf/chromophore-concentrations-absorption-and-scattering-2isu6abzhe.pdf

Chromophore concentrations, absorption and scattering properties of human skin in-vivo

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 new method is studied for estimating the hemoglobin concentration and oxygenation of a local blood layer in a human skin tissue model on the basis of visible and near infrared reflectance spectra. This method uses the iterative Monte Carlo technique for a multi-layered skin tissue model. The numerical simulation was performed to investigate the effects of estimation errors for epidermis and dermis layers on the results for the local blood layer. Experiments with skin tissue phantoms were performed to verify the possibility of this method.

Estimation of Absorbing Components in a Local Layer Embedded in the Turbid Media on the Basis of Visible to Near- Infrared (VIS-NIR) Reflectance Spectra

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.

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

Expressions are given for the three-dimensional irradiance distribution of the error-free diffraction pattern by circular apertures with a ring-shaped π-phase change. Both the amplitude distribution in the focal plane and the irradiance distribution along the optical axis have been evaluated for a large number of cases. Some interesting results are discussed and illustrated graphically. The resolving power and focal depth are taken into considerations with these apertures. Finally, some experimental results are presented.

Diffraction by Circular Apertures with a Ring-Shaped π-Phase Change

A laser Doppler microscope having a spatial resolution of about 5 µm has been constructed which has an ability of measuring the flow velocity in a microscopic area. The two kinds of Doppler-signal analyzing systems in this microscope are investigated and constructed. An example of the experimentally measured results by the laser Doppler microscope is shown.

Hiromichi Mishina

Papers

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

Estimation of Absorbing Components in a Local Layer Embedded in the Turbid Media on the Basis of Visible to Near- Infrared (VIS-NIR) Reflectance Spectra

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

Diffraction by Circular Apertures with a Ring-Shaped π-Phase Change

A Laser Doppler Microscope –Its Signal-Analyzing Systems–