Mechanisms of Laser-Tissue Interaction: Optical Properties of Tissue

Today, lasers are widely used in biology and medicine, and the majority of healthcenters and hospitals utilize modern laser systems for diagnosis and therapy applications.Researchers have introduced different medical applications for different lasers used in surgeries and other medical treatments. Medical lasers can be categorized in both diagnosis and therapy branches. Main difference between diagnosis and therapy applications is the type of laser-tissue interactions. In diagnosis, one tries to arrange a noninvasive method to study the normal behavior of tissue without any damage or clear effect on tissue. But in therapy, such as surgery, a surgeon uses laser as a knife or for affecting a specific region. So, the medical laser applications are defined by the interaction type between laser light and tissues. The knowledge of laser-tissue  interaction can help doctors or surgeons to select the optimal laser systems and modify the type of their therapy. Therefore, we seek to review the mechanisms of laser- tissue interaction. In this paper, the optical properties of biological tissue such as absorption, scattering, penetration and fluorescence are reviewed. Also, the effects of these properties on laser penetration in tissue have been explained

Mechanisms of Laser-Tissue Interaction: II. Tissue Thermal Properties

Laser-tissue interaction is of great interest due to its significant application in biomedical optics in both diagnostic and treatment purposes. Major aspects of the laser-tissue interaction which has to be considered in biomedical studies are the thermal properties of the tissue and the thermal changes caused by the interaction of light and tissue. In this review paper the effects of light on the tissue at different temperatures are discussed. Then, due to the noticeable importance of studying the heat transfer quantitatively, the equations governing this phenomenon are presented. Finally a method of medical diagnosis called thermography and some of its applications are explained

A Low-Cost Method for Optical Tomography

INTRODUCTION: In this study, arrangement of a low-cost optical tomography device compared to other methods such as frequency domain diffuse tomography or time domain diffuse tomography is reported. This low-cost diffuse optical imaging technique is based on the detection of light after propagation in tissue. These detected signals are applied to predict the location of in-homogeneities inside phantoms. The device is assessed for phantoms representing homogenous healthy breast tissues as well as those representing healthy breast tissues with a lesion inside.METHODS: A diode laser at 780nm and 50 mW is used as the light source. The scattered light is then collected from the outer surface of the phantom by a detector. Both laser and detector are fiber coupled. The detector fiber may turn around the phantom to collect light scattered at different angles. Phantoms made of intralipid as the scattering medium and ink as the absorbing medium are used as samples. Light is collected after propagation in the phantoms and the capability of the device in collecting data and detecting lesions inside the phantoms is assessed. The fact that the detection fiber orbits around the sample and detects light from various angles has eliminated the need to use several detectors and optical fibers. The results obtained from experiments are compared with the results obtained from a finite element method (FEM) solution of diffusion equation in cylindrical geometry written in FORTRAN.RESULTS: The graphs obtained experimentally and numerically are in good accordance with each other. The device has been able to detect lesions up to 13 mm inside the biological phantom.CONCLUSION: The data achieved by the optical tomography device is compared with the data achieved via a FEM code written in FORTRAN. The results indicate that the presented device is capable of providing the correct pattern of diffusely backscattered and transmitted light. The data achieved from the device is in excellent correlation with the numerical solution of the diffusion equation. Therefore, results indicate the applicability of the reported device. This device may be used as a base for an optical imaging. It is also capable of detecting lesions inside the phantom

Quantitative Analysis of Skin Erythema Due to Laser Hair Removal: A Diffusion Optical Spectroscopy Analysis

 Introduction: Laser hair removal needs an accurate understanding of tissue structure and chromophores content in order to optimize the selection of laser irradiation parameters. None of the optimized laser therapy might lead to side effects in skin tissue such as severe erythema, burn, scar etc. Therefore, guidance by a noninvasive real-time diagnostic method like optical spectroscopy technique is beneficial. The purpose of this survey is to analysis the skin hemoglobin spectrum quantitatively before and after hair removal laser irradiation to minimize the side effects of the procedure.Methods: To carry out a spectroscopy study, a halogen-tungsten light source was used in the wavelength region of 400-700 nm on an ocean optic device. The measurements were made on the facial area under identical conditions. Total 19 volunteers for laser hair removal by gentle laser Candela, ranging 14- 49 years old, were included in the study. A total of 18 spectra were taken from each person, 9 spectra before hair removal as a reference and 9 subsequent spectra. Colorimetry was done for all acquired before and after spectrums using Origin software (version 8.6). Then, the erythema index derived for each spectrum. Statistical analysis of correlation and normalization in colorimetry data were done using data analysis by SPSS (version 16).Results: Spectra analysis, before and after optical reflectance spectrums in laser hair removal procedure, revealed the subpeak derivation, and concentration on special visible wavelength 510-610 nm. We studied the changes of skin chromophores absorption. The derived erythema index [E] and colorimetry parameters a*, b*, l* were compared and correlated statistically. There was a statistically considerable direct linear correlation between a* and E while inverse linear correlation was observed for l* and E and no correlation for b* and E.Conclusion: Diffuse reflectance spectroscopy showed its potency as an accurate, noninvasive real-time as complementary method for laser treatment to detect erythema as a complication of the method, in order to optimize the parameters based on the tissue characteristics in various candidates

Quantitative Autofluorescence Imaging of A375 Human Melanoma Cell Samples: A Pilot Study

Introduction: Skin cancer is one of the most common types of malignancy worldwide. Human skin naturally contains several endogenous fluorophores, as potential sources that can emit inherent fluorescence, called intrinsic autofluorescence (AF). The melanin endogenous fluorophore in the basal cell layer of the epidermis seems to have a strong autofluorescence signal among other ones in the skin. This pilot study aimed to investigate the feasibility of the detection of autofluorescence signals in the A375 human melanoma cell line in the cell culture stage using the FluoVision optical imaging system.Methods: The human skin melanoma cell line (A375) donated as a gift from Switzerland (University Hospital Basel) was cultured. For the imaging of the A375 human melanoma cell sample in this pilot study, the FluoVision optical imaging device (Tajhiz Afarinan Noori Parseh Co) was applied. The proposed clustering image processing code was developed based on the K-mean segmentation method, using MATLAB software (version 16).Results: The quantification of color pixels in the color bar along with the intensity score of the autofluorescence signal ranged between 0 and 70 was written in the image processing code execution and a threshold higher than 40%, proportional to the ratio of autofluorescent cells. The percentage of the signal of A375 autofluorescent melanoma cells in the 3 studied cell samples was calculated as 3.11%±0.6.Conclusion: This imaging method has the advantage of no need for fluorophore labels over the existing fluorescence imaging methods, and it can be regarded as one of the important choices of label-free imaging for this A375 melanoma cell line containing the intrinsic endogenous fluorophore in cell studies. DOI: 10.34172/jlms.2021.0

Estimation of beta-carotene using calibrated reflection spectroscopy method: phantom study

In this work, we use compression and immersio

A semi-empirical analysis of dye adsorption and electron transport in dye sensitized solar cells (DSSCs)

In order to provide a comprehensive understanding of dye adsorption parameters and their relation with the structural and transport properties of dye sensitized solar cells (DSSCs), a combination of experiments and modeling of the dye adsorption and electron transport characteristics with respect to the photoanode thickness was performed. The obtained experimental data include scanning electron microscopy (SEM) images, UV-Vis data, steady state current-voltage (J-V) characteristics and open circuit voltage decay (OCVD) data. By monitoring the time evolution of the bulk dye solution and applying the fitting model, the dye loading is reproduced to determine the adsorption parameters, such as the optimum time and amount of dye loading. Additionally, the photoabsorption coefficient of the DSSCs for various active layer thicknesses was determined. In addition, the presented analysis approach builds up a relation between the dye adsorption dynamics and the structure of the nanoparticle matrix to estimate the aggregation parameters. The current-voltage characteristics are investigated for different photoanode thicknesses and the optimum thickness is determined. The discussion also highlights the importance of the localized state distribution in electron transport analysis regarding the active layer thickness by building up an analytical formalism for the OCVD, lifetime, diffusion length and nonlinearity recombination parameter (beta). It is found that considering a constant or variable b can provide fundamental interpretations for recombination pathways. The proposed integrated strategy can provide a powerful tool to study the microscopic processes and parameters governing dye-sensitized solar cell (DSSC) behavior. The presented methodology is especially applicable for the investigation of photoanodes with different morphological features such as nanotubes or nanorods, as well as different sensitizers