We constructed a movable imaging spectrograph-based system and a contact probe consisting of fibers with several source-to-detection separations (SDS) to measure spatially-resolved diffuse reflectance spectra from superficial tissue. The goal is to estimate optical properties of the mucosa in the oral cavity and investigate correlations between the estimated properties and precancerous changes in the mucosa. A previously developed GPU-based iterative curve-fitting inverse Monte Carlo model was used to extract optical properties from measured spectra. We validated the system with two-layer tissue phantoms, took in-vivo measurements on the buccal mucosa of three normal volunteers, and extracted optical parameters.
KEYWORDS: Optical properties, Reflectivity, Tissue optics, Calibration, Scattering, Monte Carlo methods, Tissues, Data modeling, Absorption, In vivo imaging
We are reporting on an experimental investigation of a movable diffuse reflectance spectroscopy system to extract diagnostically relevant optical properties of two-layered tissue phantoms simulating mucosae that are covered with stratified squamous epithelium. The reflectance spectra were measured at multiple source-detector separations using two imaging fiber bundles in contact with the phantoms, one with its optical axis perpendicular to the sample surface (perpendicular probe) and the other with its distal end beveled and optical axis tilted at 45 deg (oblique probe). Polystyrene microspheres and purified human hemoglobin were used to make tissue phantoms whose scattering and absorption properties could be well controlled and theoretically predicted. Monte Carlo simulations were used to predict the reflectance spectra for system calibration and an iterative curve fitting that simultaneously extracted the top layer reduced scattering coefficient, thickness, bottom layer reduced scattering coefficient, and hemoglobin concentration of the phantoms. The errors of the recovered parameters ranged from 7% to 20%. The oblique probe showed higher accuracy in the extracted top layer reduced scattering coefficient and thickness than the perpendicular probe. The developed system and data analysis methods provide a feasible tool to quantify the optical properties in vivo.
Diffuse reflectance spectroscopy has been applied as a non-invasive method to measure tissue optical properties, which are associate with anatomical information. The algorithm widely used to extract, optical parameters from reflectance spectra is the regression method, which is time-consuming and frequently converge to local maxima. In this study, the effects of parameters changes on spectra are analyzed in different fiber geometries, source-detector separations and wavelengths. In the end of this paper, a new fitting algorithm is proposed base on parameters features found. The new algorithm is expected to enhance the accuracy of parameters extracted and save 75% of the process time.
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