Dependence of Reflectance on Optical Properties at Short Distance (Part B: Experimental Validation).

Realistic deformable phantoms with optical properties of biological tissues for biomedical research applications

Biomedical Applications of Integrating Sphere: A Review.

The terahertz (THz) region of the electromagnetic (EM) spectrum is defined as frequencies ranging from 0.1 to 10 THz. The optical properties of biological tissues have been characterized in neighboring spectral regions; however, few studies have been conducted that have examined these properties in the THz wavelength range. In this study, we used a far-infrared optically-pumped terahertz laser system, a reflection spectrometer system, and photothermal radiometric techniques to characterize the optical properties of water and biological tissues. The reflection spectrometer system performed well at lower frequencies, but proved to be unsuitable for frequencies greater than 2.52 THz. The suboptimal performance was determined to be primarily due to the higher transmission losses of the lenses, and the increased atmospheric losses that are associated with higher terahertz frequencies. The waveguide studies corroborated these findings and served to demonstrate that purging the laser beam path with nitrogen gas was an effective way to markedly reduce THz beam propagation losses. Given this finding, we have designed a temperature-controlled, nitrogen gas purged THz enclosure. The preliminary studies using photothermal radiometric techniques appeared to provide reasonable measures for the absorption coefficient (μa) of water at THz frequencies. In future studies, the tissue property measurements will made within the custom-designed enclosure using photothermal radiometric techniques.

<i>P</i>₃ approximation of Boltzmann transport equation describes the radiance close to source with accuracy superior to diffuse approximation, which considers the high-order moments of phase function. Here, through studying the influence of two different phase functions on <i>P</i>₃ approximation, we find that the difference of diffuse reflectance in the <i>P</i>₃ approximation is distinct in about 0.45mm close to source for tissue phase function and Henyey-Greenstein (HG) phase function; tissue phase function can more character the microstructure of biological tissue than HG phase function. The research shows light for improving the accuracy of describing the radiance close to source, and of determining the optical properties of small volume tissue.

An integrating sphere system has been developed to non-invasively study the optical properties of biological tissues over a broad spectral range. Using the integrating sphere as both a diffuse illumination source and a detector provides a technically simple measurement apparatus with numerous advantages. A primary advantage is the reduction of the effect of spatial inhomogeneities on the determination of optical properties, afforded by the increased area of detection through the port-opening of the sphere, which challenges many fibre-based, spatially-resolved measurements. Through a single measurement of total diffuse reflectance, an estimation of the transport albedo of homogeneous, liquid phantoms can be made for those cases where scattering is greater than a determined threshold. Further estimations can be made to describe the absorption environment. The effects of the sphere geometry, particularly port-opening size, on the accuracy of the estimated optical properties will be discussed. These results will be used to modify the design of the integrating sphere as an efficient illuminator and light collector, in order to optimize its use in determining the optical properties of biological tissues.

Recently, non-invasive diagnostic devices using infrared light have been developed and widely use for clinical applications. To develop these devices, optical properties of biological tissue are necessary. We proposed a new optical measurement method. By using time-resolved reflectance spectroscopy and Monte Carlo simulation for the analysis of light propagation in sample, it is considered that this new method is able to measure the optical properties of small biological tissues in vivo. In this study, we investigated the possible optical property measurements of a superficial layer using this new method. As the later part of the profile of time-resolved reflectance is influenced by the optical property of the deeper layer, a time-gating technique is necessary for the measurement of the optical properties of only the superficial layer in order to use the early profile of the time-resolved reflectance measurement. The function f(t), which is described in the new method, is used for evaluation of the measurement of the superficial layer. We suggest that by using the time-gating technique for the new method and a small source-detector spacing, the optical properties of the superficial layer with a thickness is more than source-detector spacing, can be obtained.

Diabetes mellitus is a serious social and economic problem of modern society because it is widespread and fraught with numerous complications. Therefore, it is necessary to search for new methods of diabetes mellitus diagnostics and treatment and to improve the existing ones, which, in turn, requires thorough investigation of the disease development mechanisms, as well as elaboration of simple and reliable methods and criteria for detecting the complication precursors. In connection with the solution of these problems, in the paper we present an analytical review of recent publications devoted to the study of the changes of structural and optical properties of biological tissues under the conditions of diabetes mellitus development using in vitro models of glycated tissues, in vivo experimental models of diabetes in laboratory animals, and clinical studies.

We show that optical properties of dense biological tissues can be determined from backscattered power curves measured by a low-coherence reflectometer. Our measurement approach is based on a first-order scattering theory that relates the backscattered power to the total and backscattering cross sections of scatterers in a turbid medium. As a validation of the technique, measurements were made with a commercially available reflectometer on suspensions of polystyrene microspheres having known optical properties. With this reflectometer, which employs a 1300-nm LED source that emits less than 20 µW, we found that skin tissues could be probed to a depth of nearly 1 mm. Estimates of optical coefficients of human dermis and of a variety of excised animal tissues are given.

The known optical properties (absorption, scattering, total attenuation, effective attenuation, and/or anisotropy coefficients) of various biological tissues at a variety of wavelengths are reviewed. The theoretical foundations for most experimental approaches are outlined. Relations between Kubelka-Munk parameters and transport coefficients are listed. The optical properties of aorta, liver, and muscle at 633 nm are discussed in detail. An extensive bibliography is provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This study evaluates the effects of endotracheal suctioning duration on cerebral oxygenation and physiological parameters in preterm infants in intensive care. Prospective and observational study. In this study, 51 preterm infants born at 28-34 weeks of gestation in NICU were evaluated. Cerebral oxygenation was measured before, during, and after endotracheal suctioning with near-infrared spectroscopy. Pain levels of the infants were with N-PASS scale. A negative correlation was found between the lowest cerebral oxygenation value during endotracheal suctioning and the duration of endotracheal suctioning. Cerebral oxygenation levels during endotracheal suctioning were lower than pre- and post-endotracheal suctioning levels. Higher cerebral oxygenation was observed in infants whose endotracheal aspiration time was less than 13 s. The duration of endotracheal suctioning was positively correlated with pain and cerebral oxygenation stabilization time. Prolonged endotracheal suctioning duration negatively affects cerebral oxygenation in preterm infants. The study suggests an optimal endotracheal suctioning duration under 13 s. Properly executed endotracheal suctioning, with the correct technique and knowledge, can alleviate the adverse physiological effects observed in preterm infants and contribute to routine nursing care in intensive care units. This study has been reported in line with STROBE checklists. No patient or public contribution was required to design or undertake this research. Patients contributed only to the data collection. This study contributes to defining the ideal endotracheal aspiration duration, as there is not enough data so far. It showed the effect of prolonged endotracheal aspiration time on cerebral oxygenation, pain and physiological parameters in preterm infants.

The 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.

In contemporary medical engineering industry, oneof the key problems of development of methods, apparatuses, and devices for optical spectroscopy of biologicaltissues is the compilation of effective computation algorithms providing maximal accuracy and reliability ofdetermination of initial optical properties of the object ofinterest from experimental data [14, 18]. Optical properties of biological tissues can be determined from radiationfluxes measured experimentally by solving inverse problems of scattering [11], which employ different methodsof description of radiation propagation medium. In turbidlightscattering biological media (most biological mediaare turbid [22]), numerical models of transition theoryand lightscattering in turbid media should be used [8,20]. The models have a limited number of solutions.Therefore, approximate solutions are often used for practical purposes in photometry of turbid media. For example, flux Kubelka–Munk (KM) approaches are widelyused in the practice of noninvasive spectrophotometry,because they are simple and illustrative. Moreover, theKM models allow the final calculation equations to bederived in explicit analytical form [8, 12, 17, 18, 2124].In terms of transition theory and KM models, internaloptical properties of turbid media are completely characterized by linear optical extinction and scattering coefficients. The linear optical extinction and scattering coefficients are determined coefficients of differential equations describing the model. In optics, the KM models are purely photometricand phenomenological models based on heuristic principles providing separation of radiation field into discreterectangular fluxes. The principles also support the validity of linear equation of energy balance for each flux inmedium element [2, 48, 24]. In the simplest case, twoonedimensional flux KM models are considered. Suchmodel represents onedimensional radiation propagationmedium with two oppositely directed fluxes

Monte Carlo (MC) is a significant technique for finding the radiative transfer equation (RTE) solution. Nowadays, the Henyey-Greenstein (HG) scattering phase function (spf) has been widely used in most studies during the core procedure of randomly choosing scattering angles in oceanographic lidar MC simulations. However, the HG phase function does not work well at small or large scattering angles. Other spfs work well, e.g., Fournier-Forand phase function (FF); however, solving the cumulative distribution function (cdf) of the scattering phase function (even if possible) would result in a complicated formula. To avoid the above-mentioned problems, we present a semi-analytic MC radiative transfer model in this paper, which uses the cdf equation to build up a lookup table (LUT) of ψ vs. P Ψ ( ψ ) to determine scattering angles for various spfs (e.g., FF, Petzold measured particle phase function, and so on). Moreover, a lidar geometric model for analytically estimating the probability of photon scatter back to a remote receiver was developed; in particular, inhomogeneous layers are divided into voxels with different optical properties; therefore, it is useful for inhomogeneous water. First, the simulations between the inverse function method for HG cdf and the LUT method for FF cdf were compared. Then, multiple scattering and wind-driven sea surface condition effects were studied. Finally, we compared our simulation results with measurements of airborne lidar. The mean relative errors between simulation and measurements in inhomogeneous water are within 14% for the LUT method and within 22% for the inverse cdf (ICDF) method. The results suggest feasibility and effectiveness of our simulation model.

The choice of scattering phase function is critically important in the modeling of photon propagation in turbid media, particularly when the scattering path within the material is on the order of several mean free path lengths. For tissue applications, the single parameter Henyey-Greenstein (HG) phase function is known to underestimate the contribution of backscattering, while phase functions based on Mie theory can be more complex than necessary due to the multitude of parameter inputs. In this work, the two term Gegenbauer phase function is highlighted as an effective compromise between HG and Mie, as demonstrated when fitting the various phase function to measured data from phantom materials. Further comparison against the Modified Henyey-Greenstein (MHG) phase function, another two term function, demonstrates that the Gegenbauer function provides better control of the higher order phase function moments, and hence allows for a wider range of values for the similarity parameter, γ. Wavelength dependence of the Gegenbauer parameters is also investigated using a range of theoretical particle distributions. Finally, extraction of the scattering properties of solid turbid samples from angularly resolved transmission measurements is performed using an iterative Monte Carlo optimization technique. Fitting results using Gegenbauer, HG, MHG, and Mie phase functions are compared.

The phase function is an important parameter that affects the distribution of scattered radiation. In Rayleigh scattering, a scatterer is approximated by a dipole, and its phase function is analytically related to the scattering angle. For the Henyey-Greenstein (HG) approximation, the phase function preserves only the correct asymmetry factor (i.e., the first moment), which is essentially important for anisotropic scattering. When the HG function is applied to small particles, it produces a significant error in radiance. In addition, the HG function is applied only for an intensity radiative transfer. We develop a combined HG and Rayleigh (HG-Rayleigh) phase function. The HG phase function plays the role of modulator extending the application of the Rayleigh phase function for small asymmetry scattering. The HG-Rayleigh phase function guarantees the correct asymmetry factor and is valid for a polarization radiative transfer. It approaches the Rayleigh phase function for small particles. Thus the HG-Rayleigh phase function has wider applications for both intensity and polarimetric radiative transfers. For microwave radiative transfer modeling in this study, the largest errors in the brightness temperature calculations for weak asymmetry scattering are generally below 0.02 K by using the HG-Rayleigh phase function. The errors can be much larger, in the 1-3 K range, if the Rayleigh and HG functions are applied separately.