Diffuse reflectance spectroscopy with a self-calibrating fiber optic probe

Abstract

Calibration of the diffuse reflectance spectrum for instrument response and time-dependent fluctuation as well as interdevice variations is complicated, time consuming, and potentially inaccurate. We describe a novel fiber optic probe with a real-time self-calibration capability that can be used for tissue optical spectroscopy. The probe was tested in a number of liquid phantoms over a relevant range of tissue optical properties. Absorption and scattering coefficients are extracted with an average absolute error and standard deviation of 6.9% ± 7.2% and 3.5% ± 1.5%, respectively.UV-visible (UV-VIS) diffuse reflectance spectroscopy (DRS) is sensitive to the absorption and scattering properties of biological molecules in tissue and thus can be used as a noninvasive in vivo tool to obtain quantitative information about the physiological and morphological properties of human tissue. Potential clinical applications of UV-VIS DRS include precancer detection and cancer diagnostics [1][2][3], intraoperative tumor margin assessment [4], and monitoring of tumor response to chemotherapy [4], to name just a few examples. Fiber optic probes are commonly used to deliver the illumination light to and collect the diffusely reflected light from the tissue for DRS measurements [5]. For DRS to be used routinely in the clinic, calibration is required to compensate for lamp intensity fluctuations, wavelength-dependent instrument response, interdevice variations, and fiber bending losses during the measurement.Current calibration techniques typically rely on measurements using power meters, reflectance standards, and/or tissue phantoms, typically after the clinical measurements are completed. In an in vivo study of human adenomatous colon polyps, Zonios et al. developed a calibration method in which the tissue spectra were divided by the spectrum of a reference phantom made up of a 20% BaSO 4 powder suspension [1]. Utzinger et al. [2] and Mirabal et al. [3] calibrated the reflectance spectra measured from normal and neoplastic ovarian tissues and cervical tissues by the reflectance spectrum of a solution of polystyrene microspheres. Thueler et al. developed a two-step calibration procedure using a spectrally flat reflectance standard and a solid turbid siloxane phantom of known optical properties to obtain absolute reflectance spectra of stomach tissues [6]. Our group has also developed a calibration strategy for UV-VIS DRS [7]. For each instrument and probe combination a spectrum is measured from a reference phantom of known optical properties followed by a measurement from a 99% reflective Spectralon puck Labsphere, Inc.), and this is referred to as a calibrated reference phantom spectrum. Immediately after the tissue spectra are measured a spectrum is collected from the same puck. Calibration is performed by dividing the tissue spectra point by point by that of the puck. Next, the ratio of the calibrated tissue spectra and the calibrated reference spectrum is input into an inverse Monte Carlo model to extract the tissue ...

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A statistical model for removing inter-device differences in spectroscopy

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In vivoestimation of light scattering and absorption properties of rat brain using a single-reflectance fiber probe during cortical spreading depression

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