Validation of tissue optical properties measurement using diffuse reflectance spectroscopy (DRS) (original) (raw)
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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.
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.
Applied Optics, 1996
The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm 21 and absorption coefficients between 0.002 and 0.1 mm 21 showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle 1breast2, were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam.
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.
Optics and Photonics Journal
In this study, we focused on diffuse reflectance spectroscopy, a rapid and noninvasive spectroscopy technique that has considerable potential for medical diagnosis. In order to better understand and analyze the signals induced by this method, we performed a series of in vivo measurements on healthy and diseased skin. Measurement sites on a human hand and feet were chosen. Some preliminary results obtained on these sites show the feasibility of this technique in clinics.
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
Physics in Medicine and Biology, 1999
A method is described for measuring optical properties and deriving chromophore concentrations from diffuse reflection measurements at the surface of a turbid medium. The method uses a diffusion approximation model for the diffuse reflectance, in combination with models for the absorption and scattering coefficients. An optical fibre-based set-up, capable of measuring nine spectra from 400 to 1050 nm simultaneously, is used to test the method experimentally. Results of the analyses of phantom and in vivo measurements are presented. These demonstrate that in the wavelength range from 600 to 900 nm, tissue scattering can be described as a simple power dependence of the wavelength and that the tissue absorption can be accurately described by the addition of water, oxy-and deoxyhaemoglobin absorption.
Determination of tissue optical properties by steady-state spatial frequency-domain reflectometry
Lasers in Medical Science, 1998
A new non-invasive method to measure the optical properties of biological tissue is described. This method consists of illuminating the investigated sample with light which is spatially periodically modulated in intensity. The spatial modulation of the backscattered light and the diffuse reflectivity of the sample, both detected with an imaging technique, are used to deduce the absorption and reduced scattering coefficient from a table generated by Monte Carlo simulations. This principle has three major advantages: Firstly, it permits the immediate acquisition of the average values of the optical coefficients over a relatively large area (typ. 20 mm in diameter), thus avoiding the perturbations generated by small tissue heterogeneities; It also provides good flexibility for measuring the optical coefficients at various wavelengths and it does not require the use of a detector with a large dynamic range. The method was first validated on phantoms with known optical properties. Finally, we measured the optical properties of human skin at 400 nm, 500 nm, 633 nm and 700 nm in vivo.
Analysis of spectroscopic diffuse reflectance plots for different skin conditions
Spectroscopy, 2010
Optical means of characterizing tissues have gained importance due to its noninvasive nature. Spectral characteristics of the components provide useful information to identify the components, because different chromophores have different spectroscopic responses to electromagnetic waves of a certain energy band. The purpose of this study is to determine whether visible/near-infrared diffuse reflectance spectroscopy can be used to non-invasively characterize skin diseasesin vivo.An optical fiber spectrometer is set up for obtaining diffuse reflectance spectra. The method involves exposure of skin surface to white light produced by an incandescent source. The back scattered photons emerging from various layers of tissue are detected by spectrometer resulting in diffuse reflectance spectra.For the present study different skin conditions like – warts, vitiligo, thrombus (due to injury) and angioma are chosen. The spectral data obtained from the scan are plotted and compared. More or less...