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- Measurement of optical properties of normal and pathological human liver tissue from deep-UV to NIRPublication . Carneiro, Isa; Carvalho, Sónia; Henrique, Rui; Oliveira, Luís; Tuchin, Valery V.The interest of using light in clinical practice is increasing strongly and many applications work at various wavelengths from the ultraviolet to the infrared. Due to this great range of applications, the determination of the optical properties of biological tissues in a wide spectral range becomes of interest. The liver is an important organ, since it has a major role in the human body and various pathologies are known to develop within it. For these reasons, this study concerns the estimation of the optical properties of human normal and pathological (metastatic carcinoma) liver tissues between 200 and 1000 nm. The obtained optical properties present the expected wavelength dependencies for both tissues – the refractive index, the absorption and the scattering coefficients decrease with the wavelength and the anisotropy and light penetration depth increase with the wavelength. Although similar behavior was observed for the various properties between the normal and pathological tissues, evidence of smaller blood content in the pathological tissues was found. A possible explanation is that the cancer cells destroy liver’s vasculature and internal architecture, providing though a reduction in the blood content. For low wavelengths, it was observed a matching between the scattering and the reduced scattering coefficients, which implies a nearly zero anisotropy in that range. The scattering coefficient decreases from nearly 140 cm-1 (at 200 nm) to 80 cm-1 (at 1000 nm) for the normal liver and from nearly 140 cm-1 (at 200 nm) to 95 cm-1 (at 1000 nm) for the pathological tissue.
- Fast Estimation of the Spectral Optical Properties of Rabbit Pancreas and Pigment Content AnalysisPublication . Martins, Inês Soraia; Silva, Hugo Filipe; Tuchin, Valery Victorovich; Oliveira, Luís ManuelThe pancreas is a highly important organ, since it produces insulin and prevents the occurrence of diabetes. Although rare, pancreatic cancer is highly lethal, with a small life expectancy after being diagnosed. The pancreas is one of the organs less studied in the field of biophotonics. With the objective of acquiring information that can be used in the development of future applications to diagnose and treat pancreas diseases, the spectral optical properties of the rabbit pancreas were evaluated in a broad-spectral range, between 200 and 1000 nm. The method used to obtain such optical properties is simple, based almost on direct calculations from spectral measurements. The optical properties obtained show similar wavelength dependencies to the ones obtained for other tissues, but a further analysis on the spectral absorption coefficient showed that the pancreas tissues contain pigments, namely melanin, and lipofuscin. Using a simple calculation, it was possible to retrieve similar contents of these pigments from the absorption spectrum of the pancreas, which indicates that they accumulate in the same proportion as a result of the aging process. Such pigment accumulation was camouflaging the real contents of DNA, hemoglobin, and water, which were precisely evaluated after subtracting the pigment absorption.
- Lipofuscin-Type Pigment as a Marker of Colorectal CancerPublication . Carvalho, Sónia; Carneiro, Isa; Henrique, Rui; Tuchin, Valery; Oliveira, LuísThe study of the optical properties of biological tissues for a wide spectral range is necessary for the development and planning of noninvasive optical methods to be used in clinical practice. In this study, we propose a new method to calculate almost all optical properties of tissues as a function of wavelength directly from spectral measurements. Using this method, and with the exception of the reduced scattering coefficient, which was obtained by traditional simulation methods, all the other optical properties were calculated in a simple and fast manner for human and pathological colorectal tissues. The obtained results are in good agreement with previous published data, both in magnitude and in wavelength dependence. Since this method is based on spectral measurements and not on discrete-wavelength experimental data, the calculated optical properties contain spectral signatures that correspond to major tissue chromophores such as DNA and hemoglobin. Analysis of the absorption bands of hemoglobin in the wavelength dependence of the absorption spectra of normal and pathological colorectal mucosa allowed to identify differentiated accumulation of a pigment in these tissues. The increased content of this pigment in the pathological mucosa may be used for the future development of noninvasive diagnostic methods for colorectal cancer detection.
- Spectral Optical Properties of Rabbit Brain Cortex between 200 and 1000 nmPublication . Gonçalves, Tânia M.; Martins, Inês; Silva, Hugo; Tuchin, Valery V.; Oliveira, LuísThe knowledge of the optical properties of biological tissues in a wide spectral range is highly important for the development of noninvasive diagnostic or treatment procedures. The absorption coefficient is one of those properties, from which various information about tissue components can be retrieved. Using transmittance and reflectance spectral measurements acquired from ex vivo rabbit brain cortex samples allowed to calculate its optical properties in the ultraviolet to the near infrared spectral range. Melanin and lipofuscin, the two pigments that are related to the aging of tissues and cells were identified in the cortex absorption. By subtracting the absorption of these pigments from the absorption of the brain cortex, it was possible to evaluate the true ratios for the DNA/RNA and hemoglobin bands in the cortex—12.33-fold (at 260 nm), 12.02-fold (at 411 nm) and 4.47-fold (at 555 nm). Since melanin and lipofuscin accumulation increases with the aging of the brain tissues and are related to the degeneration of neurons and their death, further studies should be performed to evaluate the evolution of pigment accumulation in the brain, so that new optical methods can be developed to aid in the diagnosis and monitoring of brain diseases.
- A robust ex vivo method to evaluate the diffusion properties of agents in biological tissuesPublication . Carneiro, Isa; Carvalho, Sónia; Henrique, Rui; Oliveira, Luís; Tuchin, Valery V.A robust method is presented for evaluating the diffusion properties of chemicals in ex vivo biological tissues. Using this method that relies only on thickness and collimated transmittance measurements, the diffusion properties of glycerol, fructose, polypropylene glycol and water in muscle tissues were evaluated. Amongst other results, the diffusion coefficient of glycerol in colorectal muscle was estimated with a value of 3.3 × 10-7 cm2 /s. Due to the robustness and simplicity of the method, it can be used in other fields of biomedical engineering, namely in organ cryoprotection and food industry.
- Enhanced Ultraviolet Spectroscopy by Optical Clearing for Biomedical ApplicationsPublication . Carneiro, Isa; Carvalho, Sonia; Henrique, Rui; Selifonov, Alexey; Oliveira, Luís; Tuchin, Valery V.In this paper, we describe the combination of ultraviolet (UV) spectroscopy with the optical clearing technique to induce new tissue windows, evaluate their efficiency, study the diffusion properties of agents and discriminate cancer. The use of highly concentrated glycerol solutions has induced high efficiency clearing effects in the UV, both in human colorectal and gingival tissues. The protein dissociation rate obtained for colorectal tissues was approximately 3 times higher in pathological than in normal mucosa and the kinetics of diffuse reflectance in the UV allowed to estimate the diffusion coefficient for water in gingival mucosa at glycerol action as (1.78 ± 0.26) × 10 -6 cm 2 /s.
- Invasive and minimally invasive optical detection of pigment accumulation in brain cortexPublication . Oliveira, Luís; Gonçalves, Tânia; Pinheiro, Maria; Fernandes, Luís; Martins, Inês; Silva, Hugo; Oliveira, Hélder; Tuchin, Valery; Oliveira, LuísThe 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.
- A review of career devoted to Biophotonics – In memoriam to Ekaterina Borisova (1978–2021)Publication . Genova, Tsanislava; Avramov, Latchezar; Kolev, Boyko; Gisbrecht, Alexander; Bliznakova, Irina; Zaharieva, Lidiya; Mircheva, Victoria; Ilyov, Stoyan; Angelov, Ivan; Mantareva, Vanya; Troyanova, Petranka; Pavlova, Petya; Novikova, Tatiana; Ossikovski, Razvigor; Ivanov, Deyan; Dremin, Viktor; Rafailov, Edik U.; Sokolovsky, Sergey G.; Bykov, Alexander; Meglinski, Igor V.; Bratchenko, Ivan; Semyachkina-Glushkovskaya, Oxana; Genina, Elina; Bashkatov, Alexey N.; Bucharskaya, Alla B.; Zakharov, Valery; Spigulis, Janis; Kaniyala Melanthota, Sindhoora; K. U., Spandana; Mazumder, Nirmal; Prasad K., Shama; Townsend, Peter; Oliveira, Luís; Priezzhev, Alexander V.; Sterenborg, Dick (H.J.C.M.); Tuchin, Valery V.Regretfully, because of her sudden demise, Assoc. Prof. Ekaterina Borisova is no longer amongst us. COVID-19 pulled away a brilliant scientist during the peak of her scientific career (see Fig. 1). All authors would like to express deepest condolences and sincere support to her family, friends, relatives and colleagues! We, therefore, rightfully commemorate her dedicated and devoted contribution to biophotonics, her readiness to always support, help, motivate and inspire all her colleagues and collaborators.
- Tissue optical clearing mechanismsPublication . Yu, T.; Zhu, Dan; Genina, Elina A.; Oliveira, Luís; Bashkatov, A.N; Tuchin, V.VThe high scattering and absorption of opaque tissues limit the penetration of light into deep tissues, limiting the imaging depth of various optical imaging techniques. The proposed tissue optical clearing technique provides an innovative way to perform deep-tissue imaging. Recently, various optical clearing methods have been developed. They result in tissue clearing with similar physical principles but different chemical approaches. This chapter will introduce the mechanisms of the current tissue optical clearing methods, ranging from fundamental physical to chemical perspectives, including the main physical principle, refractive index matching; and chemical approaches such as dissociation of collagen, dehydration, delipidation, decalcification, and hyperhydration to reduce scattering, as well as the use of decolorization to reduce absorption.
- Moving tissue spectral window to the deep‐ultraviolet via optical clearingPublication . Carneiro, Isa; Carvalho, Sónia; Henrique, Rui; Oliveira, Luís; Tuchin, ValeryThe optical immersion clearing technique has been successfully applied through the last 30 years in the visible to near infrared spectral range, and has proven to be a promising method to promote the application of optical technologies in clinical practice. To investigate its potential in the ultraviolet range, collimated transmittance spectra from 200 to 1000 nm were measured from colorectal muscle samples under treatment with glycerol-water solutions. The treatments created two new optical windows with transmittance efficiency peaks at 230 and 300 nm, with magnitude increasing with glycerol concentration in the treating solution. Such discovery opens the opportunity to develop clinical procedures to perform diagnosis or treatments in the ultraviolet.
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