Evaluation of a reflectance-based approach for optical property determination in layered tissue (original) (raw)
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Reflectance-based determination of optical properties in highly attenuating tissue
Journal of Biomedical Optics, 2003
Accurate data on in vivo tissue optical properties in the ultraviolet A (UVA) to visible (VIS) range are needed to elucidate light propagation effects and to aid in identifying safe exposure limits for biomedical optical spectroscopy. We have performed a preliminary study toward the development of a diffuse reflectance system with maximum fiber separation distance of less than 2.5 mm. The ultimate objective is to perform endoscopic measurement of optical properties in the UVA to VIS. Optical property sets with uniformly and randomly distributed values were developed within the range of interest: absorption coefficients from 1 to 25 cm −1 and reduced scattering coefficients from 5 to 25 cm −1. Reflectance datasets were generated by direct measurement of Intralipid-dye tissue phantoms at =675 nm and Monte Carlo simulation of light propagation. Multivariate calibration models were generated using feed-forward artificial neural network or partial least squares algorithms. Models were calibrated and evaluated using simulated or measured reflectance datasets. The most accurate models developed-those based on a neural network and uniform optical property intervals-were able to determine absorption and reduced scattering coefficients with root mean square errors of Ϯ2 and Ϯ3 cm −1 , respectively. Measurements of ex vivo bovine liver at 543 and 633 nm were within 5 to 30% of values reported in the literature. While our technique for determination of optical properties appears feasible and moderately accurate, enhanced accuracy may be achieved through modification of the experimental system and processing algorithms.
Optics Express, 2008
A novel, multi-wavelength, fiberoptic system was constructed, evaluated and implemented to determine internal tissue optical properties at ultraviolet A (UVA) and visible (VIS) wavelengths. Inverse modeling was performed with a neural network to estimate absorption and reduced scattering coefficients based on spatially-resolved reflectance distributions. The model was calibrated with simulated reflectance datasets generated using a condensed Monte Carlo approach with absorption coefficients up to 85 cm -1 and reduced scattering coefficients up to 118 cm -1 . After theoretical and experimental evaluations of the system, optical properties of porcine bladder, colon, esophagus, oral mucosa, and liver were measured at 325, 375, 405, 445 and 532 nm. These data provide evidence that as wavelengths decrease into the UVA, the dominant tissue chromophore shifts from hemoglobin to structural proteins such as collagen. This system provides a high level of accuracy over a wide range of optical properties, and should be particularly useful for in situ characterization of highly attenuating biological tissues in the UVA-VIS.
Journal of Innovative Optical Health Sciences, 2016
Optical parameters (properties) of tissue-mimicking phantoms are determined through noninvasive optical imaging. Objective of this study is to decompose obtained diffuse reflectance into these optical properties such as absorption and scattering coefficients. To do so, transmission spectroscopy is firstly used to measure the coefficients via an experimental setup. Next, the optical properties of each characterized phantom are input for Monte Carlo (MC) simulations to get diffuse reflectance. Also, a surface image for each single phantom with its known optical properties is obliquely captured due to reflectance-based geometrical setup using CMOS camera that is positioned at 5[Formula: see text] angle to the phantoms. For the illumination of light, a laser light source at 633[Formula: see text]nm wavelength is preferred, because optical properties of different components in a biological tissue on that wavelength are nonoverlapped. During in vitro measurements, we prepared 30 different...
Broadband ultraviolet-visible optical property measurement in layered turbid media
Biomedical Optics Express, 2012
The ability to accurately measure layered biological tissue optical properties (OPs) may improve understanding of spectroscopic device performance and facilitate early cancer detection. Towards these goals, we have performed theoretical and experimental evaluations of an approach for broadband measurement of absorption and reduced scattering coefficients at ultraviolet-visible wavelengths. Our technique is based on neural network (NN) inverse models trained with diffuse reflectance data from condensed Monte Carlo simulations. Experimental measurements were performed from 350 to 600 nm with a fiber-optic-based reflectance spectroscopy system. Two-layer phantoms incorporating OPs relevant to normal and dysplastic mucosal tissue and superficial layer thicknesses of 0.22 and 0.44 mm were used to assess prediction accuracy. Results showed mean OP estimation errors of 19% from the theoretical analysis and 27% from experiments. Two-step NN modeling and nonlinear spectral fitting approaches helped improve prediction accuracy. While limitations and challenges remain, the results of this study indicate that our technique can provide moderately accurate estimates of OPs in layered turbid media.
Validation of tissue optical properties measurement using diffuse reflectance spectroscopy (DRS)
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXVIII
The effectiveness of photodynamic treatment depends on several factors including an accurate knowledge of optical properties of the tissue to be treated. Transmittance and diffuse reflectance spectroscopic techniques are commonly used to determine tissue optical properties. Although transmittance spectroscopy technique is accurate in determining tissue optical properties, it is only valid in an infinite medium and can only be used for interstitial measurements. Diffuse reflectance spectroscopy, on the other hand, is easily adapted to most tissue geometries including skin measurements that involve semi-infinte medium. However, the accuracy of the measured optical properties can be affected by uncertainty in the measurements themselves and/or due to the uncertainty in the fitting algorithm. In this study, we evaluate the accuracy of optical properties determination using diffuse reflectance spectroscopy implemented using a contact probe setup. We characterized the error of the optical properties fitted using two fitting algorithms, a wavelength wise fitting algorithm and a full reflectance spectral fitting algorithm. By conducting systematic investigation of the measurements and fitting algorithm of DRS, we gained an understanding of the uncertainties in the measured optical properties and outlined improvement measures to minimize these errors.
Broadband UV-Vis optical property measurement in layered turbid media
2011
Quantitative data on the fundamental optical properties (OPs) of biological tissue, including absorption and reduced scattering coefficients are important for elucidating light propagation during optical spectroscopy and facilitating diagnostic device design and optimization, and may enable rapid detection of early neoplasia. However, systems for in situ broadband measurement of mucosal tissue OPs in the ultraviolet-visible range have not been realized. In this study, we evaluated a fiberoptic-based reflectance system, coupled with neural network inverse models (trained with Monte Carlo simulation data), for measuring OPs in highly attenuating, two-layer turbid media. The experimental system incorporated a broadband light source, a fiberoptic probe and a CCD camera. The calibration method involved a set of standard nigrosin-microsphere phantoms as well as a more permanent spectralon phantom for quality assurance testing and recalibration. The system was experimentally evaluated using two-layer hydrogel phantoms with hemoglobin and polystyrene microspheres. The effects of tissue top-layer thickness and fitting approaches based on known absorption and scattering distributions were discussed. With our method, measurements with error less than 28% were obtained in the wavelength range of 350-630 nm.
Optical Reflectance and Transmittance of Tissues: Principles and Applications
This paper presents a discussion of diagnostic and dosi-metric optical measurements in medicine and biology. The introduction covers the topics of tissue optical properties, tissue boundary conditions , and invasive versus noninvasive measurements. Clinical applications of therapeutic dosimetry and diagnostic spectroscopy are discussed. The principles of diffuse reflectance and transmittance measurements are presented. Experimental studies illustrate reflectance spectroscopy and steady-state versus time-resolved measurements.
Validation of a fiber optic-based UVA-VIS optical property measurement system
Design and Quality for Biomedical Technologies, 2008
Tissue optical properties at ultraviolet A (UVA) and visible (VIS) wavelengths are needed to elucidate light-tissue interaction effects and optimize design parameters for spectroscopy-based neoplasia detection devices. Toward the goal of accurate and useful in vivo measurements, we have constructed and evaluated a system for optical property measurement at UVA-VIS wavelengths. Our approach involves a neural network-based inverse model calibrated with reflectance datasets simulated using a condensed Monte Carlo approach with absorption coefficients as high as 80 cm-1 and reduced scattering coefficients as high as 70 cm-1. Optical properties can be predicted with the inverse model based on spatially-resolved reflectance measured with a fiberoptic probe. Theoretical evaluation of the inverse model was performed using simulated reflectance distributions at random optical properties. Experimental evaluation involved the use of tissue phantoms constructed from bovine hemoglobin and polystyrene microspheres. An average accuracy of ±1.0 cm-1 for absorption coefficients and ±2.7 cm-1 for reduced scattering coefficients was found from realistic phantoms at five UVA-VIS wavelengths. While accounting for the very high attenuation levels near the 415 nm Soret absorption band required some modifications, our findings provide evidence that the current approach produces useful data over a wide range of optical properties, and should be particularly useful for in vivo characterization of highly attenuating biological tissues.