Supplementary document for Broadband absorption spectroscopy of heterogeneous biological tissue - 5344476.pdf (original) (raw)
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A Robust Monte Carlo Model for the Extraction of Biological Absorption and Scattering In Vivo
IEEE Transactions on Biomedical Engineering, 2000
We have a toolbox to quantify tissue optical properties that is composed of specialized fiberoptic probes for UVvisible diffuse reflectance spectroscopy and a fast, scalable inverse Monte Carlo (MC) model. In this paper, we assess the robustness of the toolbox for quantifying physiologically relevant parameters from turbid tissue-like media. In particular, we consider the effects of using different instruments, fiberoptic probes, and instrumentspecific settings for a wide range of optical properties. Additionally, we test the quantitative accuracy of the inverse MC model for extracting the biologically relevant parameters of hemoglobin saturation and total hemoglobin concentration. We also test the effect of double-absorber phantoms (hemoglobin and crocin to model the absorption of hemoglobin and beta carotene, respectively, in the breast) for a range of absorption and scattering properties. We include an assessment on which reference phantom serves as the best calibration standard to enable accurate extraction of the absorption and scattering properties of the target sample. We found the best reference-target phantom combinations to be ones with similar scattering levels. The results from these phantom studies provide a set of guidelines for extracting optical parameters from clinical studies.
Re-evaluation of model-based light-scattering spectroscopy for tissue spectroscopy
Journal of Biomedical Optics, 2009
Model-based light scattering spectroscopy (LSS) seemed a promising technique for in-vivo diagnosis of dysplasia in multiple organs. In the studies, the residual spectrum, the difference between the observed and modeled diffuse reflectance spectra, was attributed to single elastic light scattering from epithelial nuclei, and diagnostic information due to nuclear changes was extracted from it. We show that this picture is incorrect. The actual single scattering signal arising from epithelial nuclei is much smaller than the previously computed residual spectrum, and does not have the wavelength dependence characteristic of Mie scattering. Rather, the residual spectrum largely arises from assuming a uniform hemoglobin distribution. In fact, hemoglobin is packaged in blood vessels, which alters the reflectance. When we include vessel packaging, which accounts for an inhomogeneous hemoglobin distribution, in the diffuse reflectance model, the reflectance is modeled more accurately, greatly reducing the amplitude of the residual spectrum. These findings are verified via numerical estimates based on light propagation and Mie theory, tissue phantom experiments, and analysis of published data measured from Barrett's esophagus. In future studies, vessel packaging should be included in the model of diffuse reflectance and use of model-based LSS should be discontinued.
Optical Tomography and Spectroscopy of Tissue IV, 2001
We study the correlation between µ s ' and THC obtained in vitro, in a highly scattering medium containing human blood. We used a frequency domain near infrared spectrometer (modulation frequency: 110 MHz, wavelengths: 758 and 830 nm) to measure in real time (acquisition time: 0.64 s) µ s ' and THC. We used Liposyn suspension and red blood cells in saline buffer solution. After a couple of minutes of baseline acquisition, several consecutive increments of 3-5 ml blood were added to the solution yielding THC=15-100 µM and µ a =0.03-0.3 1/cm. At the last amount of blood added, increments of glucose in the range of 0.5-20 g/L were added. For each step of blood and glucose added, data were acquired for a couple of minutes. This was repeated 6 times. Average of data was calculated for both µ s ' and THC for each of the red blood cells and glucose increments added. We found a high correlation between µ s ' and THC (0.018xTHC+4.51, R 2 =0.98 at 758 nm and 0.012xTHC+4.86, R 2 =0.97 at 830 nm). We studied the effect of glucose on µ s ' and we found a high correlation between the glucose added to the suspension and the decrease in µ s ' for the case of high glucose concentrations. The slope of this correlation is-0.011 at both wavelengths and the correlation factors were R 2 =0.96 at 830 nm and R 2 =0.91 at 758 nm (case shown). The effect of glucose was less significant at 830 nm than at 758 nm in general. This work is a proof of principle for detection of µ s ' changes with glucose. This approach also establishes limits for glucose detection in physiological conditions.
In vivo absorption and scattering spectroscopy of biological tissues
Photochemical & Photobiological Sciences, 2003
Different approaches for absorption and scattering spectroscopy of living tissues are discussed. In particular, a unique system for time-resolved reflectance and transmittance spectroscopy is presented, capable of acquiring in vivo absorption and scattering spectra of diffusive media between 600 and 1000 nm. A review of typical spectra obtained from a variety of tissue structures is shown, including female breast, forearm, abdomen, and forehead. A second-level analysis of the measured spectra permits an estimation of the concentrations of the key tissue absorbers, as well as of the Mie-equivalent scattering radii. Further, absorption and scattering spectra can be used to estimate the penetration depth of light in tissues as a function of wavelength, which is a crucial parameter in view of the possible application of optical in vivo molecular imaging in clinical diagnosis. Finally, an example of the applicability of the methodology to other biological media such as fruits and vegetables is shown.
Chromophore concentrations, absorption and scattering properties of human skin in-vivo
Optics Express, 2009
Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of invivo skin in the wavelength range from 650 to 1000nm using the diffusing probe in the "modified two-layer geometry". In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000nm. It was found that the concentration of chromophores, such as oxyhemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer's size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy-and deoxy-hemoglobin as assessed at wavelengths above and below 600nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.
Quantification in tissue near-infrared spectroscopy
Philosophical Transactions of the Royal Society B: Biological Sciences, 1997
In near–infrared spectroscopy (NIRS) of tissue, light attenuation is due to: (i) absorption from chromophores of fixed concentration, (ii) absorption from chromophores of variable concentration, and (iii) light scatter. NIRS is usually concerned with trying to quantify the concentrations of chromophores in category (ii), in particular oxy– and deoxyhaemoglobin (HbO 2 and Hb) and cytochrome oxidase. In the absence of scatter the total light absorption in the medium is a linear sum of that due to each chromophore. In a scattering medium like tissue, this linear summation is distorted because the optical path length at each wavelength may differ. This distorted spectrum is then superimposed upon a further wavelength–dependent attenuation arising from light loss due to scatter, which is a complex function of the tissue absorption and scattering coefficients ( μ a and μ s ), scattering phase function, and tissue and measurement geometry. Consequently, quantification of NIRS data is diffi...
Removal of Analyte-Irrelevant Variations in Near-Infrared Tissue Spectra
Applied Spectroscopy, 2006
This paper describes mathematical techniques to correct for analyte-irrelevant optical variability in tissue spectra by combining multiple preprocessing techniques to address variability in spectral properties of tissue overlying and within the muscle. A mathematical preprocessing method called principal component analysis (PCA) loading correction is discussed for removal of inter-subject, analyte-irrelevant variations in muscle scattering from continuous-wave diffuse reflectance near-infrared (NIR) spectra. The correction is completed by orthogonalizing spectra to a set of loading vectors of the principal components obtained from principal component analysis of spectra with the same analyte value, across different subjects in the calibration set. Once the loading vectors are obtained, no knowledge of analyte values is required for future spectral correction. The method was tested on tissue-like, three-layer phantoms using partial least squares (PLS) regression to predict the absorb...
Determination of reduced scattering coefficient of biological tissue from a needle-like probe
Optics Express, 2005
Detection of interactions between light and tissue can be used to characterize the optical properties of the tissue. The purpose of this paper is to develop an algorithm that determines the reduced scattering coefficient (μ s ') of tissues from a single optical reflectance spectrum measured with a small source-detector separation. A qualitative relationship between μ s ' and optical reflectance was developed using both Monte Carlo simulations and empirical tissue calibrations for each of two fiber optic probes with 400-μm and 100-μm fibers. Optical reflectance measurements, using a standard frequency-domain oximeter, were performed to validate the calculated μ s ' values. The algorithm was useful for determining μ s ' values of in vivo human fingers and rat brain tissues.
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.