Adding-doubling Method Research Articles

Fabrication of agar-based tissue-mimicking phantom for the technical evaluation of biomedical optical imaging systems

The development process of the optical systems for various biomedical applications typically involve evaluations of technical performance. One popular evaluation method is to use a reference object such as a phantom that exhibits similar optical properties of tissue. Fabrication of a consistent phantom with known optical properties, such as scattering and absorption, is essential for accurate technical evaluation of the optical system. This paper presents a protocol for fabricating an agar-based tissue-mimicking phantom, offering practical guidance to ensure consistent and reproducible phantom creation. In addition, optical setups that measure light information required for quantifying the optical properties via an inverse adding-doubling (IAD) method are discussed. We demonstrated the fabrication of phantoms with diverse scattering and absorption properties, and the IAD method successfully quantified the optical properties. Moreover, we employed the phantom to assess the imaging depth limitation of a hyperspectral imaging system, demonstrating potential usage of phantoms for performing technical evaluation.

Effects of skin tone on photoacoustic imaging and oximetry.

Photoacoustic imaging (PAI) provides contrast based on the concentration of optical absorbers in tissue, enabling the assessment of functional physiological parameters such as blood oxygen saturation (). Recent evidence suggests that variation in melanin levels in the epidermis leads to measurement biases in optical technologies, which could potentially limit the application of these biomarkers in diverse populations. To examine the effects of skin melanin pigmentation on PAI and oximetry. We evaluated the effects of skin tone in PAI using a computational skin model, two-layer melanin-containing tissue-mimicking phantoms, and mice of a consistent genetic background with varying pigmentations. The computational skin model was validated by simulating the diffuse reflectance spectrum using the adding-doubling method, allowing us to assign our simulation parameters to approximate Fitzpatrick skin types. Monte Carlo simulations and acoustic simulations were run to obtain idealized photoacoustic images of our skin model. Photoacoustic images of the phantoms and mice were acquired using a commercial instrument. Reconstructed images were processed with linear spectral unmixing to estimate blood oxygenation. Linear unmixing results were compared with a learned unmixing approach based on gradient-boosted regression. Our computational skin model was consistent with representative literature for in vivo skin reflectance measurements. We observed consistent spectral coloring effects across all model systems, with an overestimation of and more image artifacts observed with increasing melanin concentration. The learned unmixing approach reduced the measurement bias, but predictions made at lower blood still suffered from a skin tone-dependent effect. PAI demonstrates measurement bias, including an overestimation of blood , in higher Fitzpatrick skin types. Future research should aim to characterize this effect in humans to ensure equitable application of the technology.

Optical properties and Monte Carlo multi-layered simulation of potato skin and flesh tissues

The study of optical properties of potato plays an essential role in optimizing the application of visible near-infrared (VIS-NIR) spectroscopy for nondestructive testing. This study aimed to investigate the propagation pattern of light in potato tissues and determine the depth of light penetration via a five-layer Monte Carlo simulation. A VIS-NIR integrating sphere system was used to measure the reflectance and transmittance of potato tissues in the range of 550 – 1850 nm. The absorption coefficient μa and the reduced scattering coefficient μ's were calculated using the inverse adding-doubling (IAD) method. The results demonstrated that the difference in μa between the potato skin and flesh tissues was not significant, whereas the difference in μ's was significant. The different microstructures of the potato skin and flesh tissues led to the significant difference in μ's. The results of Monte Carlo multi-layered simulations revealed that light had low reflectivity, high absorbance, and zero transmittance when propagating through the five-layer potato tissue. The wavelengths with highest and lowest absorbance were found to be 1451 and 891 nm, respectively. According to convolution (CONV) calculation results, the penetration depth of light in potato tissue was about 5.5 – 10.6 mm and the diffusion radius was 6.64 – 8.68 mm. This study provided a more accurate and usable sampling area for reflectance measurements using VIS-NIR spectroscopy. The findings of this study provided a reference for more refined non-destructive testing methods for potatoes.

Artificial neural network-based determination of denoised optical properties in double integrating spheres measurement

Accurate determination of the optical properties of biological tissues enables quantitative understanding of light propagation in these tissues for optical diagnosis and treatment applications. The absorption ([Formula: see text]) and scattering ([Formula: see text]) coefficients of biological tissues are inversely analyzed from their diffuse reflectance (R) and total transmittance (T), which are measured using a double integrating spheres (DIS) system. The inversion algorithms, for example, inverse adding doubling method and inverse Monte Carlo method, are sensitive to noise signals during the DIS measurements, resulting in reduced accuracy during determination. In this study, we propose an artificial neural network (ANN) to estimate [Formula: see text] and [Formula: see text] at a target wavelength from the R and T spectra measured via the DIS to reduce noise in the optical properties. Approximate models of the optical properties and Monte Carlo calculations that simulated the DIS measurements were used to generate spectral datasets comprising [Formula: see text], [Formula: see text], R and T. Measurement noise signals were added to R and T, and the ANN model was then trained using the noise-added datasets. Numerical results showed that the trained ANN model reduced the effects of noise in [Formula: see text] and [Formula: see text] estimation. Experimental verification indicated noise-reduced estimation from the R and T values measured by the DIS with a small number of scans on average, resulting in measurement time reduction. The results demonstrated the noise robustness of the proposed ANN-based method for optical properties determination and will contribute to shorter DIS measurement times, thus reducing changes in the optical properties due to desiccation of the samples.

Characterization of bulk optical properties of pear tissues in the 500 to 1000 nm range as input for simulation-based optimization of laser spectroscopy in diffuse transmittance mode

Insight in the transmission of light through intact fruit is important to optimize and interpret the signals acquired with spectroscopy methods such as tunable diode laser absorption spectroscopy (TDLAS). To this end, we quantified the bulk optical properties (BOP) of skin, outer cortex, inner cortex, and core tissue of three pear ( Pyrus communis ) cultivars ( Thimo , Cepuna , and Conference ) using double integrating spheres measurements in combination with the inverse adding doubling method. Similar trends and values were observed for the bulk optical properties of the three cultivars. A clear chlorophyll-a absorption feature was present in the bulk absorption coefficient ( μ a ) at 690 nm for the skin samples. At 761 nm, the bulk scattering coefficient ( μ s ) decreased from the skin towards the core region, for example from 256 ± 34 cm −1 to 146 ± 22 cm −1 for Conference pears. The observed anisotropy factor ( g ) of the skin was lower than these of the other tissue layers (0.87 ± 0.026 vs. 0.94 ± 0.08 for Conference ). Next, Monte Carlo voxelized media (MCVM) simulations were performed based on these BOP values and validated against measurements with a TDLAS setup for gas in scattering media absorption spectroscopy (GASMAS) at 761 nm. In these experiments, the sample thickness was reduced by sequentially slicing the pear from the skin towards the center. Light transmittance through an intact pear at the height of the core region was found to be very low (1.9 × 10 −4 ± 8.5 × 10 −5 %) and exponentially increased around 100-fold when the sample thickness decreased from 64 mm to 24 mm. The simulated transmittance profiles based on the measured BOP values at 761 nm followed the same trend as the measured GASMAS transmittance as a function of the fruit thickness. This shows that simulations based on these measured BOP values can be used to optimize the measurement configuration for O 2 monitoring in intact pear fruit with GASMAS. • The bulk optical properties of pear tissue layers: skin, outer cortex, inner cortex, and core. • 3D Monte Carlo simulation of diffuse transmittance through an intact pear. • Comparison of simulated and measured diffuse transmittance vs pear sample thicknesses. • Simulations provided a valuable tool for optimizing the amplification of GASMAS detectors in diffuse transmittance mode.

Investigation of the Optical Properties of Indium Tin Oxide Thin Films by Double Integration Sphere Combined with the Numerical IAD Method.

Transparent conductive electrodes have become essential components of numerous optoelectronic devices. However, their optical properties are typically characterized by the direct transmittance achieved by making use of spectrophotometers, avoiding an in-depth knowledge of the processes involved in radiation attenuation. A different procedure based on the Double Integration Sphere combined with the numerical Inverse Adding-Doubling (IAD) method is employed in this work to provide a comprehensive description of the physical processes limiting the light transmittance in commercial indium tin oxide (ITO) deposited on flexible PET samples, highlighting the noticeable contribution of light scattering on the total extinction of radiation. Moreover, harnessing their flexibility, the samples were subjected to different mechanical stresses to assess their impact on the material's optical and electrical properties.

A comparative study of the optical and microstructural properties of suspension and atmospheric plasma sprayed thermal barrier coatings

Thermal radiation is an increasingly important issue for thermal barrier coating (TBC) applications in aircraft engine components. As operating temperatures increase, the radiative part of the heat load increases significantly faster than the conductive portion; as such, TBCs may not be as efficient in protecting their underlying heat-sensitive metallic components. To address this issue, new coating morphologies must be investigated. In this study, we compare the optical performance of atmospheric plasma sprayed (APS) and suspension plasma sprayed (SPS) yttria-stabilized zirconia (YSZ) coatings. First, we extract their absorption and scattering coefficients from spectrophotometry measurements via the inverse adding-doubling (IAD) method. The microstructure of the coatings is then analyzed and compared using scanning electron microscopy (SEM) and mercury infiltration porosimetry (MIP). SPS samples are found to offer higher radiation blocking properties due to a more uniform distribution of pores with an average smaller pore diameter than the APS samples. This results in an overall higher pore density, with each pore interface acting as a scattering site, and therefore a higher propensity for scattering events.

Sky polarization pattern under multi-layer environment of atmosphere and sea fog

The vertical polarization distribution pattern of sea fog multilayer media and skylight in the atmosphere is explored. To change the complicated maritime environment, the simplified double layer structure of the atmosphere and sea fog is employed, and the scattering coefficients of the uniform atmosphere and sea fog medium are derived using the Rayleigh and Mie scattering methods, respectively. Using the adding-doubling method (RT3) based on the vector radiation transmission equation, the transmission of radiation between the two layers of the medium is calculated to obtain the polarization distribution conditions of skylight, and the variation tendency of the polarization characteristics observed from the ground is studied for the downwelling radiation of sea fog on the meridian of the Sun. An indoor sea fog setting was employed to perform the polarization transmission test, and the relationship between humidity, light intensity transmittance, and polarization degree was explored. The data suggest that the Sun’s position gives the lowest degree of polarization (DOP), and that the maximum value is obtained when the angle between the solar altitude angle and the observed altitude angle is 90°. Short wavelength lasers have a higher influence on optical transmittance than long wavelength lasers do when humidity levels increase. The circular polarization effect of long wavelength laser is better in damp surroundings.

Polarized discrete ordinate adding approximation for infrared and microwave radiative transfer

A POLarized Discrete ordinate aDding Approximation (POLDDA) is proposed to solve the vector thermal radiative transfer equation in a vertically inhomogeneous plane-parallel atmosphere. The discrete ordinates method is employed to find the single-layer solution for vector thermal radiative transfer; this is an extension of the approach for scalar radiative transfer, with the I- and Q-components being dealt with in a parallel way by using a doubled dimension in the discrete ordinate space. Chandrasekhar’s invariance principle is used to drive the adding process for the connection of multiple layers. This adding process has no restriction on the layer optical properties. The accuracy and efficiency of POLDDA are evaluated under different atmospheric conditions for different number of computational quadrature angles (streams). It is shown that the relative differences between POLDDA (using 32 or 16 streams) and the benchmark calculations (PolRadtran/RT3 with 32 streams, a typical model based on the adding-doubling method) are negligible for both I- and Q-components. When 8 streams are used, the accuracy of POLDDA slightly decreases, but still higher than that of 8-stream RT3. The computational efficiency of POLDDA is much higher than RT3, especially for large optical depths and when a large number of streams (≥ 16) are used. Unlike RT3, the computational time of POLDDA is always the same regardless of the optical depth.

Scalar thermal radiation using the adding-doubling method.

The scalar radiative transfer equation in the presence of thermal radiation source is solved in detail, using the adding-doubling method; Planck functions within any given layer are assumed to possess constant, linear, or exponential parameterizations with optical thickness. The radiance profile in any zenith direction is calculated directly in terms of matrix inversions. The inputs to the model are the inherent optical properties (layer total single-scattering albedos, scattering phase functions, and optical thickness) along with temperature and altitude profiles, and the top of the atmosphere and ground surface boundary conditions. The algorithm is implemented in a state-of-the-art MATLAB program, with the cosmic microwave background as the source at the upper boundary and a Lambertian surface reflection at the lower boundary. The simulations are validated against the VLIDORT discrete ordinate radiative transfer model. Results are compared in detail for cases with linear and exponential Planck function parameterizations.

Simulation of light interaction with seedless grapes.

Spectroscopic techniques are widely used for the non-destructive maturation and quality monitoring of different fruits. To develop new sensor devices for this purpose, knowing the optical properties of the agricultural sample is crucial for enabling the prediction of the interaction of the incident light with the fruit. In the present study, the optical properties of three different seedless grape varieties (ARRA15, Tawny and Melody/Blagratwo) were determined from 400 to 1000 nm using a UV-visible/near-infrared spectrometer with an integrating sphere and subsequent calculation of the absorption and scattering coefficients and the anisotropy factor using the inverse adding doubling method. The results indicate that the optical properties of different grape varieties have significant differences, especially in the visible wavelength region, whereas these are less distinct in the near-infrared range. Independent of grape variety, the grape berry skin has a higher scattering coefficient and scattering occurs predominantly in the forward direction. Based on the optical properties of the grape berries, a three-dimensional grape berry model is generated within OpticStudio (Zemax, LLC) for the different varieties that can be used in optical illumination simulations. The bulk scattering inside the fruit is modeled by the Henyey-Greenstein distribution. A comparison of the simulated values for the total transmission and the specular reflection determined experimentally shows that realistic optical grape models can be created within OpticStudio. Overall, the procedure for creating optical grape models presented here will be helpful for the development of optical applications used in pre- and post-harvest food quality monitoring. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Spectral Radiative Properties of Polydispersed SiO2 Particle Beds

The focus of this work is on the measurement and analysis of the radiative properties of polycrystalline particle beds with various layer thicknesses. The particles are polydispersed with average diameters of 222, 150, and . The spectral, directional–hemispherical reflectance and transmittance of the particle bed are measured at wavelengths from 0.4 to using a monochromator, and the reflectance measurement is extended to using a Fourier-transform infrared spectrometer. Particles are closely packed between two transparent windows for measuring the radiative properties. In the visible and near-infrared region up to , the inverse adding–doubling method yields the effective absorption and scattering coefficients. The results suggest that short wavelength absorption needs to be included in modeling the behavior of particle beds due to multiple scattering. A discrete-scale Monte Carlo ray-tracing method is developed to model the radiative properties by assuming monodispersed spherical particles, and the simulated results compare well with measurements. The effective absorption and scattering coefficients of the particle beds obtained from the independent scattering theory are compared to those from the inverse method. The impact of dependent scattering on the packed beds is observed for smaller-sized particles.

Changes in Optical Properties of Model Cholangiocarcinoma after Plasmon-Resonant Photothermal Treatment

The heating degree of the inner layers of tumor tissue is an important parameter required to optimize plasmonic photothermal therapy (PPT). This study reports the optical properties of tissue layers of transplanted cholangiocarcinoma and covering tissues in rats without treatment (control group) and after PPT using gold nanorods (experimental group). PPT was carried out for 15 min, and the temperature on the skin surface reached 54.8 ± 1.6 °C. The following samples were cut out ex vivo and studied: skin, subcutaneous connective tissue, tumor capsule, top, center, and bottom part of the tumor. The samples’ absorption and reduced scattering coefficients were calculated using the inverse adding–doubling method at 350–2250 nm wavelength. Diffuse reflectance spectra of skin surface above tumors were measured in vivo in the control and experimental groups before and immediately after PPT in the wavelength range of 350–2150 nm. Our results indicate significant differences between the optical properties of the tissues before and after PPT. The differences are attributed to edema and hemorrhage in the surface layers, tissue dehydration of the deep tumor layers, and morphological changes during the heating.

In-situ quantitative monitoring the organic contaminants uptake onto suspended microplastics in aquatic environments

Microplastics act as a source of organic contaminants in aquatic environments and thus affect their environmental fate and toxicity. Because of the weak and reversible interactions between microplastics and organic species, the organic coronas vary with their surrounding environments. Thus, in order to evaluate the possible environmental risks of microplastics, methods for evaluating the dynamic uptake of organic contaminants onto suspended microplastics in aquatic environments are greatly desired. In this work, a UV–vis spectroscopy-based approach was developed for in-situ monitoring organic contaminants uptake onto suspended microplastics after correcting the light scattering interference from microplastics suspensions and establishing the nonlinear relationship between concentration and light absorbance of organic species. The inverse adding-doubling method based on radiative transfer theory was adopted to correct the light scattering effect of suspensions. Then, the resulting mixed absorption spectra were decomposed to calculate the concentrations of the aqueous and adsorbed organic species simultaneously with a nonlinear calibration method. The uptake processes of bisphenol A and p-nitrophenol onto nylon 66 microparticles were monitored with this approach and confirmed by high-performance liquid chromatography analysis. The approach was validated by applying it to natural water samples, and the equilibrium adsorption capacity was found to be interfered mainly by the protein-like substances. This approach has high accuracy, good reproducibility, remarkable universality, and ease of handling, and also provides a potential tool for characterizing the corona formation process on suspended particles both in natural and artificial environments, such as eco-corona formation and engineering surface modification on nano/micro-particles.

Monte-Carlo optical model coupled with Inverse Adding-Doubling for Building Integrated Photovoltaic smart window design and characterisation

Building Integrated Photovoltaic (BIPV) glazings are promising technologies with the benefits of electricity generation, solar shading and building energy savings. A new approach is to integrate BIPV windows with thermotropic materials such as Hydroxypropyl Cellulose (HPC) hydrogel, which offers adaptive advantages for the systems to respond to time-varying weather conditions but also enhances the PV electricity generation. To design such systems, knowledge of the temperature-dependent scattering properties of the selected thermotropic materials is of significance. In this study, a Building Integrated Photovoltaic (BIPV) smart window system consisting of a thermotropic membrane synthesised using HPC and gellan gum gelling agent for electricity generation and also solar control has been designed and investigated. An advanced optical model, which combines a Monte-Carlo ray-tracing technique with an Inverse Adding-Doubling (IAD) method, has been developed for characterising the thermotropic membrane in terms of angular scattering distribution under various membrane temperatures and HPC concentrations. Then the developed optical model has been validated by comparison with experimental measurements. Subsequently, the validated optical model has been used to design and optimise the proposed BIPV smart window. The effects of HPC concentration, geometric concentration ratio, thermotropic membrane thickness and glass refractive index on PV power outputs have been evaluated. Finally, a prototype of the BIPV smart window with a 6 wt% HPC membrane has been manufactured and tested under indoor conditions. From the experimental tests, it was found that the total transmittance of the double-pane glass sample with a 6 wt% HPC membrane layer decreases from approximately 90%to 14%, when the membrane temperature increases from 27 °C to 56 °C. The measured short-circuit current for the prototype BIPV smart window is up to 1.15 times higher than that of its counterpart system with a similar PV area but no membrane.

Light propagation within N95 filtered face respirators: A simulation study for UVC decontamination.

This study presents numerical simulations of UVC light propagation through seven different filtered face respirators (FFR) to determine their suitability for Ultraviolet germicidal inactivation (UVGI). UV propagation was modeled using the FullMonte program for two external light illuminations. The optical properties of the dominant three layers were determined using the inverse adding doubling method. The resulting fluence rate volume histograms and the lowest fluence rate recorded in the modeled volume, sometimes in the nW cm-2 , provide feedback on a respirator's suitability for UVGI and the required exposure time for a given light source. While UVGI can present an economical approach to extend an FFR's useable lifetime, it requires careful optimization of the illumination setup and selection of appropriate respirators.

Evaluation of the optical and biomechanical properties of bioengineered human skin generated with fibrin-agarose biomaterials.

.Significance: Recent generation of bioengineered human skin allowed the efficient treatment of patients with severe skin defects. However, the optical and biomechanical properties of these models are not known.Aim: Three models of bioengineered human skin based on fibrin-agarose biomaterials (acellular, dermal skin substitutes, and complete dermoepidermal skin substitutes) were generated and analyzed.Approach: Optical and biomechanical properties of these artificial human skin substitutes were investigated using the inverse adding-doubling method and tensile tests, respectively.Results: The analysis of the optical properties revealed that the model that most resembled the optical behavior of the native human skin in terms of absorption and scattering properties was the dermoepidermal human skin substitutes after 7 to 14 days in culture. The time-course evaluation of the biomechanical parameters showed that the dermoepidermal substitutes displayed significant higher values than acellular and dermal skin substitutes for all parameters analyzed and did not differ from the control skin for traction deformation, stress, and strain at fracture break.Conclusions: We demonstrate the crucial role of the cells from a physical point of view, confirming that a bioengineered dermoepidermal human skin substitute based on fibrin-agarose biomaterials is able to fulfill the minimal requirements for skin transplants for future clinical use at early stages of in vitro development.

Effects of optical variables in a single integrating sphere system on estimation of scattering properties of turbid media

This research was aimed at determining the effect of optical variables for a single integrating sphere system, coupled with the inverse adding-doubling method, on estimating the reduced scattering coefficient ( μ s ′ ) of turbid media. Integrating sphere measurements were performed on a total of 36 liquid samples and two solid samples. The results demonstrated that the system had good accuracy, with average errors for estimating absorption coefficient μa (pure absorption) and μ s ′ (pure scattering) of liquid samples being 15.0% and 4.7% over 550–900 nm, compared with the collimated transmittance and empirical equation, respectively. The system also had good reproducibility for μa and μ s ′ , with the coefficients of variation lower than 4%. Sensitivity analysis revealed that the detectable values of μa and μ s ′ were around 0.02 cm−1 and 4.5 cm−1. Entrance and detector port diameters, standard reflectivity and anisotropy factor had a negligible effect on estimating μ s ′ ( μ s ′ (2.8%–35.3%). Hence these variables should be carefully chosen or accurately measured before optical property measurements are carried out. Application examples of the μ s ′ estimation for apple skin and flesh further validated the system performance, indicating that appropriate selection of optical variables could improve the estimation of μ s ′ .

Biomedical Applications of Integrating Sphere: A Review.

Integrating sphere remains a valuable tool for biomedical optics research. Specifically, it has been used to determine the optical properties (i.e., absorption coefficient, scattering coefficient and anisotropy factor) of biological tissues. This study presents an overview of the literature on integrating sphere and its biomedical applications. In particular, we start with a brief introduction of tissue optics with emphasis on the optical properties of biological tissues, followed by a detailed discussion of the hardware and related procedures of the integrated sphere system. Both the experimental procedure and subsequent analytical models (i.e., first order scattering, Kubelka Munk, diffusion approximation, Monte Carlo and inverse adding-doubling methods) along with illustrative examples are also outlined. Finally, illustrative examples to explore the optical properties of tissue phantoms and biological samples have been discussed. This survey will provide a ready reference and overview for the applications of integrating sphere in biomedical optics.

Application and evaluation of the small-angle approximation on forward radiative transfer model

The small-angle approximation is used in solving the radiative transfer equation when the single-scattering phase function has a strong forward peak. The original vector radiative transfer equation is decomposed into three equations: the forward, the regular, and the correction ones. The forward equation can be efficiently solved using the small-angle approximation. The solution of the regular equation is given by the adding-doubling method in this study. The correction equation including cross terms between the forward and the regular quantities is given and analyzed. The combined model associated with the forward and regular equations is further verified in the forward radiative transfer model, where the molecular absorptions with respect to the standard atmospheric profiles are taken into consideration using the line-by-line method. Great agreements are given between the combined model and the model using the straight adding-doubling method.