Turbid phantoms play a crucial role in evaluating optical systems and estimating optical properties. Liquid phantoms offer precise tuning of optical properties, but accurately determining their scattering properties is challenging. By using aqueous suspensions of standardized polystyrene microspheres, their optical properties can be theoretically derived using Mie theory. The parameters involved in calculating the scattering coefficient and phase function of microspheres in a liquid medium include the refractive index, density, size probability distribution and solid content of the microspheres and refractive index of the medium. The accuracy of these parameters directly affects the accuracy of calculated optical properties. A lack of clear protocols for phantom preparation and conflicting data in the literature may lead to easily avoidable inaccuracies. We introduce an open-source software that offers a detailed mixing protocol and subsequent optical property calculations for turbid phantoms. The software allows users to input details of the microsphere suspension, target optical property values, and choose between individual or sequentially diluted phantom mixing. It also accommodates the introduction of non-scattering molecular dyes to achieve specific absorption coefficients. The software facilitates recalculations of optical properties based on the actual quantities used during phantom preparation, offering flexibility and increased accuracy. Error estimates are provided using Monte Carlo sampling and error propagation. The open-source software is established as a comprehensive tool for preparing liquid turbid phantoms using microsphere suspensions, accessible to non-experts with basic familiarity of pipetting and use of analytical scales.
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.
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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