Abstract
We propose a new method for estimating the reduced scattering coefficient, μs', of turbid homogeneous samples using Spatially Offset Raman Spectroscopy (SORS). The concept is based around the variation of Raman signal with SORS spatial offset that is strongly μs'-dependent, as such, permitting the determination of μs'. The evaluation is carried out under the assumptions that absorption is negligible at the laser and Raman wavelengths and μs' is approximately the same for those two wavelengths. These conditions are often satisfied for samples analyzed in the NIR region of the spectrum where SORS is traditionally deployed. Through a calibration procedure on a PTFE model sample, it was possible to estimate the μs' coefficient of different turbid samples with an error (RMSEP) below 18%. The knowledge of μs' in the NIR range is highly valuable for facilitating accurate numerical simulations to optimize illumination and collection geometries in SORS, to derive in-depth information about the properties of SORS measurements or in other photon applications, dependent on photon propagation in turbid media with general impact across fields such as biomedical, pharmaceutical, security, forensic, and cultural sciences.
Highlights
We propose a new method for estimating the reduced scattering coefficient, μs′, of turbid homogeneous samples using Spatially Offset Raman Spectroscopy (SORS)
We propose a simple, alternative concept enabling the estimation of the scattering coefficient of homogeneous samples using only Spatially Offset Raman Spectroscopy (SORS) data.[4]
We presented a new approach for estimating the value of transport length and reduced scattering coefficient μs′ of turbid media using SORS in the approximation of ideal pointillumination/collection geometry
Summary
All Raman experiments were performed on a SORS system previously described.[45]. In brief, we used a NIR laser with 830 nm wavelength and 200 mW power measured at the sample. The predicted average reduced scattering coefficient values were 1.2, 0.7, 2.6, and 0.49 mm−1 for PTFE, PE, PS, and the ex vivo tissue, respectively, were obtained this way from the first-principles without any calibration by matching the observed Raman signal decay to that derived from Monte Carlo simulations For each sample and each spatial offset, the values of μs′ estimated from the intensities of different Raman bands of the sample were averaged in order to obtain a mean value of the reduced scattering coefficient in the near-infrared spectral range (850− 900 nm). The proposed approach allowed the estimation of the scattering coefficient of turbid media with an error (RMSEP) below 18% (0.070 mm−1 for ex vivo tissue; Figure 3 and Table 2) These results validate the use of this approach for the estimation of the scattering coefficient of turbid media from the sole decay of Raman scattering intensity over spatial offset
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