Abstract
Multi-diameter single fiber reflectance (MDSFR) spectroscopy enables quantitative measurement of tissue optical properties, including the reduced scattering coefficient and the phase function parameter γ. However, the accuracy and speed of the procedure are currently limited by the need for co-localized measurements using multiple fiber optic probes with different fiber diameters. This study demonstrates the use of a coherent fiber bundle acting as a single fiber with a variable diameter for the purposes of MDSFR spectroscopy. Using Intralipid optical phantoms with reduced scattering coefficients between 0.24 and 3 mm−1, we find that the spectral reflectance and effective path lengths measured by the fiber bundle (NA = 0.40) are equivalent to those measured by single solid-core fibers (NA = 0.22) for fiber diameters between 0.4 and 1.0 mm (r ≥ 0.997). This one-to-one correlation may hold for a 0.2 mm fiber diameter as well (r = 0.816); however, the experimental system used in this study suffers from a low signal-to-noise for small dimensionless reduced scattering coefficients due to spurious back reflections within the experimental system. Based on these results, the coherent fiber bundle is suitable for use as a variable-diameter fiber in clinical MDSFR quantification of tissue optical properties.
Highlights
White light reflectance spectroscopy provides non-invasive measurement of tissue optical properties, which can yield diagnostic information about tissue microstructure and physiology [1,2,3,4]
As a result of the low signal-to-noise ratio (SNR), longer integration times were used with the fiber bundle, varying from 4000 ms to 8000 ms, to be compared with integration times of 50 ms to 300 ms used with the solid-core fibers
We have presented the use of selective light coupling into and out of portions of a coherent fiber bundle to achieve a variable-diameter fiber for Multi-diameter single fiber reflectance (MDSFR) spectroscopy
Summary
White light reflectance spectroscopy provides non-invasive measurement of tissue optical properties, which can yield diagnostic information about tissue microstructure and physiology [1,2,3,4]. Reflectance spectra contain the combined effects of all the absorbing and scattering constituents in the optically sampled volume, which makes quantitative analysis of reflectance spectra complicated To address this challenge, our group has recently developed a semi-empirical model for single fiber reflectance (SFR) spectroscopy based upon an experimentally validated Monte Carlo simulation [5]. SFR spectroscopy utilizes a simple fiber geometry in which a single fiber is used for both delivery of illumination light and collection of reflected light This compact geometry allows for easy incorporation of SFR into narrow-gauge endoscopic instruments, such as fine needle aspiration (FNA) needles [6, 7], and confines the optically sampled volume to shallow depths [8], which may be useful for investigating precancerous lesions in epithelial tissue. Using an empirical model for the effective photon path length, we have shown that SFR can be used to quantify the tissue absorption coefficient (μa) to investigate tissue chromophores without a priori knowledge of the tissue scattering properties [9]
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