We investigate age-related changes of the dermal reduced scattering coefficient in human skin using a recently introduced methodology for non-invasive characterization of structure and composition of skin in vivo. The approach combines pulsed photothermal radiometry (PPTR) with diffuse reflectance spectroscopy (DRS) in visible part of the spectrum. The experimental data are fitted simultaneously with the respective predictions of a dedicated numerical model of light and heat transport in healthy skin (i.e., inverse Monte Carlo). For this purpose, we apply a four-layer optical skin model consisting of epidermis, upper dermis, lower dermis, and subcutaneous adipose tissue. The study is based on 24 measurements of test sites on the ventral side of the forearm in 9 women and 9 men with healthy fair skin, between 20 and 65 years old. Linear regression analysis of the assessed dermal reduced scattering coefficient values at 500 nm (ader) indicated no significant variation with the person’s age. Meanwhile, strong correlations of ader with the blood contents in both papillary and reticular dermis were observed. Separating the respective contributions of these three variables using multiple linear regression (MLR) analysis revealed a highly significant influence of person’s age on ader (with Pearson’s correlation coefficient r = –0.55 and p < 0.0001). Specifically, by excluding the direct influence of the dermal blood contents, ader decreases with age by approximately 0.2 mm-1 per decade. In addition, the values obtained for older persons are in good agreement with the results from a large cohort study performed by Jonasson et al. (J. Biomed. Opt. 2018).
We explore the potential for noninvasive monitoring of laser tattoo removal treatment by adapting a recently introduced methodology for quantitative assessment of structure and composition of human skin in vivo.1 The approach combines diffuse reflectance spectroscopy in visible part of the spectrum with pulsed photothermal radiometry, involving timeresolved measurements of mid-infrared emission after irradiation with a millisecond laser pulse. The experimental data are fitted simultaneously with the respective predictions of a dedicated numerical model of light and heat transport in tattooed skin. For this purpose we apply a three-layer optical model of skin, consisting of epidermis, upper dermis, and lower dermis which includes the tattoo ink. This proof of principle study involved one healthy volunteer undergoing tattoo removal treatment. One half of the tattoo was treated with 5 ns pulses from a commercial Nd:YAG laser (StarWalker® MaQX, Fotona) at radiant exposure of 3 J/cm2, and the other half with much shorter, "picosecond" pulses at the same wavelength and 1.3 J/cm2. Measurements were performed before and 8 weeks after the first treatment session, as well as 20 weeks after the second treatment. The results show a significant reduction of the ink content and an increase of the subsurface depth of the tattoo layer over the course of treatment with both lasers, in agreement with gradual fading of the tattoo.
We have recently introduced a novel methodology for noninvasive assessment of structure and composition of human skin in vivo1. The approach combines pulsed photothermal radiometry, involving time-resolved measurements of midinfrared emission after irradiation with a millisecond light pulse, and diffuse reflectance spectroscopy in visible part of the spectrum (400–600 nm). The experimental data are fitted simultaneously with respective predictions from a fourlayer Monte Carlo model of light transport in human skin. The described approach allows assessment of the contents of specific chromophores (melanin, oxy-, and deoxy-hemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis.
In present study we evaluate the potential of this approach for quantitative evaluation of tattoos. For this purpose, we apply a three-layer optical model of skin consisting of epidermis, upper dermis, and bottom dermis which includes the tattoo ink. The study involves healthy volunteer with black tattoo undergoing tattoo removal treatment with Q-switched Nd:YAG laser. The measurements are performed in four tattoo sites and one nearby healthy site before and after laser removal treatment. The results indicate the depth of tattoo, amount of tattoo ink and scattering properties in the dermis. This information can be used to improve our understanding of laser tattoo removal procedure.
Assessment of bruise age in forensic investigations is based on skin discoloration due to dynamic processes involving extravasated hemoglobin and products of its biochemical decomposition. However, the current protocol relies exclusively on visual inspection and subjective assessment by a medical expert. We are aiming at development of an objective and more accurate approach to aging of bruises by utilizing two optical techniques: Diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR).
This report involves two human volunteers with bruises acquired incidentally at a known time point. DRS spectra in visible spectral range are obtained from laterally uniform lesion sites using an integrating sphere. PPTR measurements involve irradiation with a millisecond laser pulse at 532 nm and recording the resulting transient change of mid-infrared emission with a fast infrared camera. Data from both measurements are analyzed simultaneously by fitting with predictions from a dedicated numerical simulation of light and heat transport in a multi-layer model of human skin. The results show a prominent increase of the dermal hemoglobin content and reduction of its oxygenation level relative to a nearby intact site (resulting from blood extravasation), followed by a rise of the bilirubin content. The parameters of a simple dynamical model of a self-healing bruise are then assessed by fitting together a set of experimental data acquired at different times post injury. The results indicate a rise and subsequent decrease of the hemoglobin decomposition rate, as the inflammatory response first kicks in and then gradually subsides.
Study of bruise characteristics and evolution is of much interest in forensic sciences, with many objective techniques being researched. In this study we combine the optical methods of diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR) to measure signals from healthy and bruised skin. From these measurements we first obtain initial physiological parameters for a four-layer model of healthy skin near the bruised site. A bruise model is constructed by inserting a blood pool into this baseline model to simulate a bruise followed by bruise dynamics simulation for PPTR signals of bruises. Obtained bruise dynamics parameters describe the evolution of the bruise. The results show that the choice of a suitable healthy baseline affects bruise parameters obtained by fitting the simulated signals to the measurements. By using healthy skin baselines with similar melanin and papillary blood fractions during analysis, comparable bruise parameters are obtained. Differences in layer thickness and scattering properties of healthy skin did not significantly influence these parameters. In contrast, higher papillary blood content in one site resulted in considerably different bruise parameters. Our findings show the importance of good determination of a healthy baseline, preferably using the baseline obtained by a simultaneous fitting of multiple measurements.
We have recently introduced a novel methodology for noninvasive assessment of structure and composition of human skin in vivo. The approach combines pulsed photothermal radiometry (PPTR), involving time-resolved measurements of midinfrared emission after irradiation with a millisecond light pulse, and diffuse reflectance spectroscopy (DRS) in visible part of the spectrum (400–600 nm). The experimental data are fitted simultaneously with respective predictions from a four-layer Monte Carlo (MC) model of light transport in human skin. The described approach allows assessment of the contents of specific chromophores (melanin, oxy-, and deoxyhemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis. However, the involved multidimensional optimization with a numerical forward model (i.e., inverse MC, IMC) is computationally very expensive. In addition, each optimization task is repeated several times to control the inevitable numerical noise and facilitate escape from local minima. Thus, assessment of 14 free parameters from each radiometric transient and DRS spectrum takes several hours despite massive parallelization using CUDA technology and a high-performance graphics card. To alleviate this limitation, we have developed a computationally very efficient predictive model (PM) based on machine learning technology. The PM is an ensemble of decision trees (random forest), trained using ~10,000 "pairs" of various skin parameter combinations and the corresponding PPTR signals and DRS spectra, computed using our forward MC model. While the parameter values predicted by the PM are very similar to the IMC results there are some concerns regarding their accuracy. Therefore, we present here a hybrid model, which combines the described PM and IMC approaches.
We have recently introduced a novel methodology for noninvasive assessment of structure and composition of human skin in vivo. The approach combines pulsed photothermal radiometry (PPTR), involving time-resolved measurements of mid-infrared emission after irradiation with a millisecond light pulse, and diffuse reflectance spectroscopy (DRS) in visible part of the spectrum (400–600 nm). The experimental data are fitted simultaneously with respective predictions from a four-layer Monte Carlo (MC) model of light transport in human skin. The described approach allows assessment of the contents of specific chromophores (melanin, oxy-, and deoxyhemoglobin), as well as scattering properties and thicknesses of the epidermis and dermis. However, the involved multidimensional optimization with a numerical forward model (i.e., inverse MC) is computationally very expensive. In addition, each optimization task is repeated several times to control the inevitable numerical noise and facilitate escape from local minima. Thus, assessment of 14 free parameters from each radiometric transient and DRS spectrum takes several hours despite massive parallelization using CUDA technology and a high-performance graphics card. To alleviate this limitation, we have constructed a computationally very efficient predictive model (PM) based on machine learning. The PM is an ensemble of decision trees (random forest), trained using ~11,000 "pairs" of various skin parameter combinations and the corresponding PPTR signals and DRS spectra, computed using our forward MC model. We analyze the performance of such a PM by means of cross-validation and comparison with the inverse MC approach.
Combination of diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR) was recently successfully used to study evolution of accidental traumatic bruises. Yet, accidental bruises introduce many unknowns into the evolution analysis and thus a more controllable and repeatable approach for bruising is desired. In this study, evolution of bruises induced by aluminum projectiles of known mass and velocity were studied by DRS and PPTR. Bruises were induced on volar forearm skin of two healthy volunteers. Inverse Monte Carlo including four-layer skin model, was used to analyze the DRS and PPTR data to determine skin chromophores, their concentrations and depths. For bruise analysis, a bruise model was constructed and evolved according to hemoglobin diffusion kinetics. Bruise analysis of PPTR signals yielded bruise evolution parameters, most importantly hemoglobin diffusion constant, hemoglobin decomposition time and blood pool depth. The study results show that chronological tracking of hemoglobin decomposition can be assessed by the combined DRS and PPTR technique on induced bruise. Parameters of individual bruises were compared and two trends in chronological behavior of hemoglobin decomposition time discerned. Changes in bruise diffuse reflectance spectra were noted. Induced bruise parameters, however, still showed some scatter and thus further research is needed to reduce bruise variability.
Objective determination of bruise age is still done mainly by visual inspection, however, because of insufficient information the method provides, another mode is desired. In this study, determination of bruise dynamics parameters with a four-layer model and individually determined scattering parameters was carried out. Pulsed photometric radiometry signals and diffuse reflectance spectra were recorded during the healing process for volunteers with accidental bruises. Parameters of healthy skin were obtained and used as input parameters for the bruise model. Hence, the difference in signals would be fully attributed to changes caused by the injury. Results of three bruises on the arm and the analysis of one on the outer side of the arm are presented showing bruise dynamics parameters and their dependency on bruise severity. Objective determination of bruise dynamics parameters is achieved by use of pulsed photothermal radiometry via a four-layer optical model of human skin and inverse Monte Carlo analysis with predetermined input parameters of healthy skin.
Caffeine is the most widely consumed psychoactive substance in the world. It affects many tissues and organs, in particular central nervous system, heart, and blood vessels. The effect of caffeine on vascular smooth muscle cells is an initial transient contraction followed by significant vasodilatation. In this study we investigate the use of diffuse reflectance spectroscopy (DRS) for monitoring of vascular changes in human skin induced by caffeine consumption. DRS spectra were recorded on volar sides of the forearms of ten healthy volunteers at time delays of 0, 30, 60, 120, and 180 minutes after consumption of caffeine, while one subject served as a negative control. Analytical diffusion approximation solutions for diffuse reflectance from three-layer structures were used to assess skin composition (e.g., dermal blood volume fraction and oxygen saturation) by fitting to experimental data. The results demonstrate that cutaneous vasodynamics induced by caffeine consumption can be monitored by DRS, while changes in the control subject not consuming caffeine were insignificant.
We present a novel methodology for quantitative analysis of hemodynamics in human skin in vivo. Our approach combines pulsed photothermal radiometry (i.e., time-resolved measurements of midinfrared emission from sample surface after exposure to a short light pulse) and diffuse reflectance spectroscopy in visible part of the spectrum. Experimental data are fitted with predictions of a numerical model of light transport in a four-layer skin model (i.e., inverse Monte Carlo), which allows assessment of the layer thicknesses, chromophore contents (e.g., melanin, oxy- and deoxy-hemoglobin), as well as scattering properties. The performance is tested in comparison analysis of healthy skin before and during application of a blood pressure cuff (at 200 mm Hg) for 5 minutes.
We have combined two optical techniques to enable simultaneous assessment of structure and composition of human
skin in vivo: Pulsed photothermal radiometry (PPTR), which involves measurements of transient dynamics in midinfrared
emission from sample surface after exposure to a light pulse, and diffuse reflectance spectroscopy (DRS) in
visible part of the spectrum. Namely, while PPTR is highly sensitive to depth distribution of selected absorbers, DRS
provides spectral information and thus enables differentiation between various chromophores. The accuracy and
robustness of the inverse analysis is thus considerably improved compared to use of either technique on its own.
Our analysis approach is simultaneous multi-dimensional fitting of the measured PPTR signals and DRS with
predictions from a numerical model of light-tissue interaction (a.k.a. inverse Monte Carlo). By using a three-layer skin
model (epidermis, dermis, and subcutis), we obtain a good match between the experimental and modeling data.
However, dividing the dermis into two separate layers (i.e., papillary and reticular dermis) helps to bring all assessed
parameter values within anatomically and physiologically plausible intervals.
Both the quality of the fit and the assessed parameter values depend somewhat on the assumed scattering properties for
skin, which vary in literature and likely depend on subject's age and gender, anatomical site, etc. In our preliminary
experience, simultaneous fitting of the scattering properties is possible and leads to considerable improvement of the fit.
The described approach may thus have a potential for simultaneous determination of absorption and scattering properties
of human skin in vivo.
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