In vivo quantification of the scattering properties of tissue using multi-diameter single fiber reflectance spectroscopy

Abstract

Multi diameter single fiber reflectance (MDSFR) spectroscopy is a non-invasive optical technique based on using multiple fibers of different diameters to determine both the reduced scattering coefficient (μs') and a parameter γ that is related to the angular distribution of scattering, where γ = (1-g2)/(1-g1) and g1 and g2 the first and second moment of the phase function, respectively. Here we present the first in vivo MDSFR measurements of μs'(λ) and γ(λ) and their wavelength dependence. MDSFR is performed on nineteen mice in four tissue types including skin, liver, normal tongue and in an orthotopic oral squamous cell carcinoma. The wavelength-dependent slope of μs'(λ) (scattering power) is significantly higher for tongue and skin than for oral cancer and liver. The reduced scattering coefficient at 800 nm of oral cancer is significantly higher than of normal tongue and liver. Gamma generally increases with increasing wavelength; for tumor it increases monotonically with wavelength, while for skin, liver and tongue γ(λ) reaches a plateau or even decreases for longer wavelengths. The mean γ(λ) in the wavelength range 400-850 nm is highest for liver (1.87 ± 0.07) and lowest for skin (1.37 ± 0.14). Gamma of tumor and normal tongue falls in between these values where tumor exhibits a higher average γ(λ) (1.72 ± 0.09) than normal tongue (1.58 ± 0.07). This study shows the potential of using light scattering spectroscopy to optically characterize tissue in vivo.

Keywords: (060.2310) Fiber optics; (170.6510) Spectroscopy, tissue diagnostics; (170.6935) Tissue characterization; (300.6550) Spectroscopy, visible.

Fig. 1

Schematic diagram of the measurement setup. Reflectance and fluorescence are measured through a single fiber of either 0.4 or 0.8 mm. Two identical setups are used to accommodate 2 fiber diameters.

Fig. 2

Confocal fluorescence microscopy image of mouse tongue, using 488 nm excitation and 520-540 nm detection, showing the distribution of GFP-expressing OSC tumor in green and transmitted 488 nm light in grey. Scale bar 1 mm.

Fig. 3

Typical 0.8 mm SFR data. Plotted are the measured R_SF (black dots), individual SFR fits (solid lines) and calculated_{$R_{SF}^0$}(dashed lines) for normal tongue, tumor, skin and liver tissue.

Fig. 4

Averaged SFR spectra of normal tongue tissue; fiber diameters are 0.4 and 0.8 mm.

Fig. 5

μ_s′ (a) and γ (b) for different tissues, measured in 1 representative mouse.

Fig. 6

Gamma per tissue, averaged over n = 19.

Fig. 7

Average scattering power (a), μ_s′ (800nm) (b) and Gamma (c) of 19 mice, for 4 different tissues.