Abstract
With the objective to study the variation of optical properties of rat muscle during optical clearing, we have performed a set of optical measurements from that kind of tissue. The measurements performed were total transmittance, collimated transmittance, specular reflectance and total reflectance. This set of measurements is sufficient to determine diffuse reflectance and absorbance of the sample, also necessary to estimate the optical properties. All the performed measurements and calculated quantities will be used later in inverse Monte Carlo (IMC) simulations to determine the evolution of the optical properties of muscle during treatments with ethylene glycol and glucose. The results obtained with the measurements already provide some information about the optical clearing treatments applied to the muscle and translate the mechanisms of turning the tissue more transparent and sequence of regimes of optical clearing.

Abstract
Optical properties of biological tissues are unique and may be used for tissue identification, tissue discrimination or even to identify pathologies. Early stage colorectal cancer evolves from adenomatous polyps that arise in the inner layer of the colorectal tube - the mucosa. The identification of different optical properties between healthy and pathological colorectal tissues might be used to identify different tissue components and to develop an early stage diagnosis method using optical technologies. Since most of the biomedical optics techniques use light within the visible and near infrared wavelength ranges, we used the inverse adding-doubling method to make a fast estimation of the optical properties of colorectal mucosa and early stage adenocarcinoma between 400 and 1000 nm. The estimated wavelength dependencies have provided information about higher lipid content in healthy mucosa and higher blood content in pathological tissue. Such data has also indicated that the wavelength dependence of the scattering coefficient for healthy mucosa is dominated by Rayleigh scattering and for pathological mucosa it is dominated by Mie scattering. Such difference indicates smaller scatterer size in healthy mucosa tissue. Such information can now be used to develop new diagnosis or treatment methods for early cancer detection or removal. One possibility is to use optical clearing technique to improve tissue transparency and create localized and temporary tissue dehydration for image contrast improvement during diagnosis or polyp laser removal. Such techniques can now be developed based on the different results that we have found for healthy and pathological colorectal mucosa.

Abstract
Colorectal carcinoma is a major health concern worldwide and its high incidence and mortality require accurate screening methods. Following endoscopic examination, polyps must be removed for histopathological characterization. Aiming to contribute to the improvement of current endoscopy methods of colorectal carcinoma screening or even for future development of laser treatment procedures, we studied the diffusion properties of glucose and water in colorectal healthy and pathological mucosa. These parameters characterize the tissue dehydration and the refractive index matching mechanisms of optical clearing (OC). We used ex vivo tissues to measure the collimated transmittance spectra and thickness during treatments with OC solutions containing glucose in different concentrations. These time dependencies allowed for estimating the diffusion time and diffusion coefficient values of glucose and water in both types of tissues. The measured diffusion times for glucose in healthy and pathological mucosa samples were 299.2 +/- 4.7 s and 320.6 +/- 10.6 s for 40% and 35% glucose concentrations, respectively. Such a difference indicates a slower glucose diffusion in cancer tissues, which originate from their ability to trap far more glucose than healthy tissues. We have also found a higher free water content in cancerous tissue that is estimated as 64.4% instead of 59.4% for healthy mucosa. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract
The optical dispersion and water content of human liver were experimentally studied to estimate the optical dispersions of tissue scatterers and dry matter. Using temporal measurements of collimated transmittance [T-c(t)] of liver samples under treatment at different glycerol concentrations, free water and diffusion coefficient (D-gl) of glycerol in liver were found as 60.0% and 8.2 x 10(-7) cm(2)/s, respectively. Bound water was calculated as the difference between the reported total water of 74.5% and found free water. The optical dispersion of liver was calculated from the measurements of refractive index (Rl) of tissue samples made for different wavelengths between 400 and 1000 nm. Using liver and water optical dispersions at 20 degrees C and the free and total water, the dispersions for liver scatterers and dry matter were calculated. The estimated dispersions present a decreasing behavior with wavelength. The dry matter dispersion shows higher Rl values than liver scatterers, as expected. Considering 600 nm, dry matter has an Rl of 1.508, whereas scatterers have an Rl of 1.444. These dispersions are useful to characterize the Rl matching mechanism in optical clearing treatments, provided that [T-c(t)] and thickness measurements are performed during treatment. The knowledge of D-gl is also important for living tissue cryoprotection applications. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract
In this study, we used machine learning techniques to reconstruct the wavelength dependence of the absorption coefficient of human normal and pathological colorectal mucosa tissues. Using only diffuse reflectance spectra from the ex vivo mucosa tissues as input to algorithms, several approaches were tried before obtaining good matching between the generated absorption coefficients and the ones previously calculated for the mucosa tissues from invasive experimental spectral measurements. Considering the optimized match for the results generated with the multilayer perceptron regression method, we were able to identify differentiated accumulation of lipofuscin in the absorption coefficient spectra of both mucosa tissues as we have done before with the corresponding results calculated directly from invasive measurements. Considering the random forest regressor algorithm, the estimated absorption coefficient spectra almost matched the ones previously calculated. By subtracting the absorption of lipofuscin from these spectra, we obtained similar hemoglobin ratios at 410/550 nm: 18.9-fold/9.3-fold for the healthy mucosa and 46.6-fold/24.2-fold for the pathological mucosa, while from direct calculations, those ratios were 19.7-fold/10.1-fold for the healthy mucosa and 33.1-fold/17.3-fold for the pathological mucosa. The higher values obtained in this study indicate a higher blood content in the pathological samples used to measure the diffuse reflectance spectra. In light of such accuracy and sensibility to the presence of hidden absorbers, with a different accumulation between healthy and pathological tissues, good perspectives become available to develop minimally invasive spectroscopy methods for in vivo early detection and monitoring of colorectal cancer.

Abstract
The estimation of the spectral absorption coefficient of biological tissues provides valuable information that can be used in diagnostic procedures. Such estimation can be made using direct calculations from invasive spectral measurements or though machine learning algorithms based on noninvasive or minimally invasive spectral measurements. Since in a noninvasive approach, the number of measurements is limited, an exploratory study to investigate the use of artificial generated data in machine learning techniques was performed to evaluate the spectral absorption coefficient of the brain cortex. Considering the spectral absorption coefficient that was calculated directly from invasive measurements as reference, the similar spectra that were estimated through different machine learning approaches were able to provide comparable information in terms of pigment, DNA and blood contents in the cortex. The best estimated results were obtained based only on the experimental measurements, but it was also observed that artificially generated spectra can be used in the estimations to increase accuracy, provided that a significant number of experimental spectra are available both to generate the complementary artificial spectra and to estimate the resulting absorption spectrum of the tissue. © 2022 Journal of Biomedical Photonics & Engineering. © J-BPE.