Separation of absorption and scattering properties of turbid media using relative spectrally resolved cw radiance measurements

Abstract

We present a new method for extracting the effective attenuation coefficient and the diffusion coefficient from relative spectrally resolved cw radiance measurements using the diffusion approximation. The method is validated on both simulated and experimental radiance data sets using Intralipid-1% as a test platform. The effective attenuation coefficient is determined from a simple algebraic expression constructed from a ratio of two radiance measurements at two different source-detector separations and the same 90° angle. The diffusion coefficient is determined from another ratio constructed from two radiance measurements at two angles (0° and 180°) and the same source-detector separation. The conditions of the validity of the method as well as possible practical applications are discussed.

Keywords: (170.3660) Light propagation in tissues; (170.6510) Spectroscopy, tissue diagnostics; (170.6935) Tissue characterization; (170.7050) Turbid media; (290.4210) Multiple scattering.

Fig. 1

Schematic representation of responses of the turbid media to external stimuli used in various measurement approaches.

Fig. 2

A schematic of the experimental setup for radiance measurements.

Fig. 3

A comparison of optical parameters extracted from simulated data (lines) with actual parameters obtained from basic characterization experiments (symbols): a) extracted μ_eff(λ) based on Eq. (3) for different pairs of source–detector separations, b) extracted D(λ) based on Eq. (5) for different source–detector separations.

Fig. 4

A comparison of optical parameters extracted from experimental radiance data (lines) with actual parameters obtained from basic characterization experiments (symbols): (a) extracted μ_eff(λ) based on Eq. (3) for different pairs of source–detector separations, (b) extracted D(λ) based on Eq. (5) for different source–detector separations.

Fig. 5

A comparison of (a) ${\mu }_a(\lambda )$ and (b) ${{\mu }^{\prime }}_s(\lambda )$ expressed from non-corrected ${\mu }_{eff}(\lambda )$ and $D(\lambda )$obtained from experimental radiance data (lines) with those expressed from actual values of ${\mu }_{eff}(\lambda )$ and $D(\lambda )$ obtained from basic characterization measurements (symbols).

Fig. 6

Normalized to maximum at 0° angular radiance from analytical solution of RTE (solid red line) and from diffusion approximation (dashed blue line) for 850 nm and 10-mm source–detector separation.