A fiberoptic reflectance probe with multiple source-collector separations to increase the dynamic range of derived tissue optical absorption and scattering coefficients

Abstract

Measurement of tissue optical absorption and (transport) reduced scattering coefficients (mu(a) and mu(s)', respectively) is fundamental to many applications of light in medicine and biology. We report a handheld fiberoptic probe to determine these coefficients by measuring the diffuse reflectance at multiple source-collector distances, which allows for a larger dynamic range than a single source-collector separation. Diffusion theory and a priori knowledge of the spectral shape of mu(a) and mu(s)' are used in a forward model of the diffuse reflectance. The dynamic range and accuracy of this method were evaluated using Monte Carlo simulations, phantom experiments and tissues in vivo.

Early biomarker for radiation-induced wounds: day one post-irradiation assessment using hemoglobin concentration measured from diffuse optical reflectance spectroscopy

“…DOS measurements were performed using a previously reported reflectance system [18,20,21] optimized for skin depth quantification (~1-2 mm) and is described here for completeness (Fig. 1).…”

“…An in-house data acquisition program was used to acquire sequential reflectance spectra (within ~1-3 s) that include background readings. The probe was calibrated for absolute reflectance [20,21]. All raw measurements were background and noise floor subtracted and post-processed to remove variations in LED output.…”

“…All raw measurements were background and noise floor subtracted and post-processed to remove variations in LED output. The processed reflectance measurements were fit using a diffusion theory model of light transport that was previously well validated for the described probe geometry and expected optical properties of biological tissues with our wavelength analysis range (450-650 nm) [20,21]. The fitting algorithm was spectrally constrained for the absorption spectrum using known chromophore spectra of oxy-, ( ) oxyHb a μ λ , and deoxy-…”

Single-fiber diffuse optical time-of-flight spectroscopy

“…Contrary to similar steady-state approaches [1][2][3][6][7][8], the "average" absorption in a larger volume is measured, not just what is immediately in front of the fiber. Extraction of the scattering coefficient, providing structural information, may be possible in sufficiently homogeneous materials but would require careful calibration of the equipment.…”

“…Minimally invasive in vivo spectroscopy based on needle-guided optical fibers is an attractive tool for medical applications, from tissue diagnostics in general to characterization of suspect tissue lesions [1][2][3][4][5][6][7][8]. Ensuring that spectroscopic signals are representative of the tissue studied is of major concern, and it is not a simple matter.…”