Reflectance-based determination of optical properties in highly attenuating tissue (original) (raw)
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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.
Evaluation of a reflectance-based approach for optical property determination in layered tissue
Design and Quality for Biomedical Technologies II, 2009
In order to elucidate light propagation mechanisms involved in optical spectroscopy devices, the optical properties of layered mucosal tissues at ultraviolet and visible wavelengths are needed. Previous approaches to measuring this data have typically been based on spatially-resolved reflectance. However, these approaches have limitations, some of which are not well understood. Therefore, the objectives of this study were (1) to elucidate the relationship between spatiallyresolved reflectance distributions and optical properties in two-layer tissue models and (2) introduce and assess an unconstrained approach to optical property measurement. The first part of this study involved calculating reflectance from two-layer tissue for a wide variety of optical property combinations (μ a = 1-22.5, μ s ' = 5-42.5 cm-1) using a Monte Carlo scaling technique. In the second part, a neural network inverse model trained with the aforementioned results was evaluated using simulated reflectance data. This relationship between optical properties and reflectance provides fundamental insights into the strengths, weaknesses and potential limitations of strategies for optical property measurement based on spatially-resolved reflectance. The neural network approach estimated optical property values with a degree of accuracy that depended on the probe geometry (5-, 6-, 10-and 11-fiber probes were simulated). The average error in determination of μ a ranged from 15 to 51% and average error for μ s ' ranged from 8 to 32%. While computationally expensive to develop, neural network models calibrated with simulation data may prove to be a highly effective approach for rapid, unconstrained estimation of the optical properties of two-layer tissues.
Journal of Biomedical Optics, 2005
Determination of tissue optical properties is fundamental for application of light in either therapeutical or diagnostics procedures. In the present work we implemented a spatially resolved steady-state diffuse reflectance method where only two fibers (one source and one detector) spaced 2.5 mm apart are used for the determination of the optical properties. The method relies on the spectral characteristics of the tissue chromophores (water, dry tissue, and blood) and the assumption of a simple wavelength dependent expression for the determination of the reduced scattering coefficient. Because of the probe dimensions the method is suited for endoscopic measurements. The method was validated against more traditional models, such as the diffusion theory combined with adding doubling for in vitro measurements of bovine muscle. Mean and standard deviation of the absorption coefficient and the reduced scattering coefficient at 630 nm for normal mucosa were 0.87Ϯ0.22 cm −1 and 7.8 Ϯ2.3 cm −1 , respectively. Cancerous mucosa had values 1.87Ϯ1.10 cm −1 and 8.4Ϯ2.3 cm −1 , respectively. These values are similar to data presented by other authors. Blood perfusion was the main variable accounting for differences in the absorption coefficient between the studied tissues.
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.
Clinical determination of tissue optical properties by endoscopic spatially resolved reflectometry
Applied Optics, 1996
A noninvasive method to measure the optical properties of a diffusing and absorbing medium is described. Based on the spatially resolved measurement of diffuse reflectance at the sample surface, this method is particularly suitable for investigating the in vivo optical properties of biological tissues endoscopically in a clinical context. The sensitivity of the measurement is discussed, and two optical probes for two different clinical applications are presented. Preliminary measurements are performed on a nonbiological medium, which illustrate the possibilities of the proposed method. Finally, we report on in vivo measurements of the optical properties of the human esophageal wall at 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.
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...
Lasers in surgery and …, 1994
This study examines the validity of optical property measurements by comparing surface temperatures rises predicted by a well-tested mathematical model with temperatures measured experimentally during laser irradiation. Analysis is based on the early temperature response that is proportional to the absorption coefficient. The results of the investigation suggest that values for tissue absorption coefficient can be greatly overestimated when current spectrophotometric techniques are used. This seems especially true when a broad light beam and a low portto-beam-size ratio are used for transmission and reflection measurements with an integrating sphere. o
Optical properties of biological tissues: a review
This corrigendum corrects a mistake in , showing anisotropy versus wavelength, in which the breast data from were misplotted and mislabelled. The corrected figure is given here as figure 8(a). (b) shows a close-up of the data from Peters et al (1990), presenting the wavelength dependence of the anisotropy of scattering for the five types of tissue in breast. (a) Figure 8. (a) Corrected version of figure 8, showing anisotropy of scattering versus wavelength. (b) Detail of data from Peters et al (1990), showing wavelength dependence of anisotropy of scattering for the five types of tissue in breast.