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.

We present in vivo human total retinal blood flow measurements using Doppler Fourier domain optical coherence tomography (OCT). The scan pattern consisted of two concentric circles around the optic nerve head, transecting all retinal branch arteries and veins. The relative positions of each blood vessel in the two OCT conic cross sections were measured and used to determine the angle between the OCT beam and the vessel. The measured angle and the Doppler shift profile were used to compute blood flow in the blood vessel. The flows in the branch veins was summed to give the total retinal blood flow at one time point. Each measurement of total retinal blood flow was completed within 2 s and averaged. The total retinal venous flow was measured in one eye each of two volunteers. The results were 52.90+/-2.75 and 45.23+/-3.18 microlmin, respectively. Volumetric flow rate positively correlated with vessel diameter. This new technique may be useful in the diagnosis and treatment of optic nerve and retinal diseases that are associated with poor blood flow, such as glaucoma and diabetic retinopathy.

/pdf/retinal-blood-flow-measurement-by-circumpapillary-fourier-1d396vnosh.pdf

Retinal blood flow measurement by circumpapillary Fourier domain Doppler optical coherence tomography.

An enhanced structure for compact and high sensitivity plasmonic refractive index sensor by using the coupling of two metal-insulator-metal (MIM) waveguides with a silver nanorods array embedded into a square resonator is proposed and analyzed in this paper. We placed silver nanorods inside the resonator due to their unique optical properties in nanoscale confinement and low propagation losses. Based on obtained results, the resonance wavelengths of the sensor having an approximate linear relationship with the refractive index of the materials under detecting that are placed into the square resonator. With an optimum design and considering a tradeoff among detected power, structure size and sensitivity, the finite difference time domain simulations show that the refractive index and temperature sensitivity values can be obtained as high as 2320 nm per refractive index unit (RIU) and 0.84 nm/°C. The achieved sensor can be used in nanophotonic and plasmonic integrated circuits and in this research; we show its applicability for the detection of different human blood groups as well.

High sensitivity plasmonic refractive index sensing and its application for human blood group identification

In this study, the design of refractive index sensor with high sensitivity would be provided. This consists of a metal substrate with two metal-insulator-metal waveguide and an array of hexagonal nanoholes. Using the refractive index model obtained for different blood groups A, B, and O, we show that the structure can be used as a sensor to determine a human blood group. We used the array of nanoholes due to the unique optical properties, which leads to nanoscale confinement, high sensitivity to surface, and low propagation losses. Based on the results, resonance wavelength has a linear relationship with the refractive index of a material that is placed inside the nanohole; this feature makes it easy to identify the material. Considering a tradeoff between the transmitted power, structure size, and sensitivity, finite-difference time-domain simulations show that the sensitivity can be as large as 3172 nm per refractive index unit. In general, our plasmonic sensor can promote the sensitivity through the phenomenon of plasmon exciting on the surface of the nanoholes and would have useful applications in the medical field such as determining blood group, hemoglobin, and deoxyribonucleic acid (DNA) quantification.

Engineering Hexagonal Array of Nanoholes for High Sensitivity Biosensor and Application for Human Blood Group Detection

Knowledge of the optical properties of human whole blood has always been of great interest for medical applications. The aim of this study was to provide the dispersive relations of refractive index of human whole blood with different types in the visible and near-infrared ranges and other conditions. In order to overcome the scattering effect, we applied an unusual method based on total internal reflection. A focused light, a semicylindrical lens in contact with tissues and a linear CCD camera are used in the experimental apparatus. The critical angle and therefore the refractive index can be obtained from the spacial distribution of internal reflective light. A monochromator is chosen as the light source, the chromatic dispersion curve of materials can be determined directly and quickly. A set of values has been presented that relates the refractive index to wavelength and types of whole, undiluted blood. Our results suggest that the refractive dispersions be almost the same in the visible and near-infrared ranges no matter which blood type it belongs to. In addition, the relationship can be described by Cauchy's formula.

Refractive index of human whole blood with different types in the visible and near-infrared ranges

Biomedical optics involves with individual index of refraction of biological tissue. A new method to measure refractive index and the accuracy analysis as well is presented. The characteristic includes the incident angle is changed with parallel movement of incident beam and the refractive index of sample is determined linearly. A narrow laser beam and quarter-cylindrical lens in contact with a sample are applied in the apparatus. The device can provide the index for various tissue samples with no complex mathematical analysis and the calibration of device is simple. A number of indices for human tissue have been determined at 632.8 nm.

Linear method of determining the refractive index of biotissue

An equivalent particle size distribution function n(r) is applied to describe optical scattering property of tissue. Under the Fraunhofer diffraction approximation, both the scattering coefficient μs and the scattering phase function S(θ) are educible from n(r). Moreover, such a scheme provides a new feasible method based on the light scattering techniques for particle size analysis to measure the optical properties of tissue. Experimental results of the whole human blood and a thin porcine muscle sample are also provided and so is a calculation resulting from an optical phantom of tissue. The light scattering equivalency between the practical tissue and the corresponding equivalent particles has been verified.

https://iopscience.iop.org/article/10.1088/0256-307X/16/4/022/pdf

Light scattering properties of biotissue versus equivalent particle size distribution

The main significance about the refractive index of bio- tissue, its measurement methods and its thermal properties in particular are presented in this paper. Most of bio-tissue can be regarded as random dispersed medium which inhomogeneous dimension is about the order of micrometers. In order to describe the optical behaviors of bio-tissue, we have to use the imaginary scattering and absorption properties. Meanwhile, an apparent index of refraction, or average refractive index has to be introduced to solve various boundary and temporal problems. Two possible measurement methods in which the experimental creativity is reflected are provided. We applied one of experimental setups to study the thermal response of refractive index of bio-tissue. Experimental results suggest that the index be temperature dependent on the process of heating. The tissues used in these experiments were porcine muscles. These measurements were taken at the 632.8 nm. The index of refraction keeps stable levels (1.364 +/- 0.001) below 36 Celsius degrees and (1.387 +/- 0.005) above 60 Celsius degrees, respectively, but increases with an increase in temperature from 36 to 60 Celsius degrees. The heating and cooling procedures are irreversible in optical property of tissue.

Refractive index of biotissue and its thermal response

Based on the Monte Carlo modeling of light transport in tissue, the relations of the diffuse reflectance between the optical parameters are studied intensively. The authors presented a new diffuse reflectance fitted formula in which the refractive indices of tissues are included.

Shusen Xie

Papers

Refractive index of human whole blood with different types in the visible and near-infrared ranges

Linear method of determining the refractive index of biotissue

Light scattering properties of biotissue versus equivalent particle size distribution

Refractive index of biotissue and its thermal response

Diffuse reflectance from biological tissues