Quantitative Raman spectroscopy in turbid media

Abstract

Intrinsic Raman spectra of biological tissue are distorted by the influences of tissue absorption and scattering, which significantly challenge signal quantification. A combined Raman and spatially resolved reflectance setup is introduced to measure the absorption coefficient ? a and the reduced scattering coefficient ?' s of the tissue, together with the Raman signals. The influence of ? a and ?' s on the resonance Raman signal of ?-carotene is measured at 1524 cm -1 by tissue phantom measurements and Monte Carlo simulations for ? a=0.01 to 10 mm -1 and ?' s=0.1 to 10 mm -1. Both methods show that the Raman signal drops roughly proportional to 1/? a for ? a>0.2 mm -1 in the measurement geometry and that the influence of ?' s is weaker, but not negligible. Possible correction functions dependent on the elastic diffuse reflectance are investigated to correct the Raman signal for the influence of ? a and ?' s, provided that ? a and ?' s are measured as well. A correction function based on the Monte Carlo simulation of Raman signals is suggested as an alternative. Both approaches strongly reduce the turbidity-induced variation of the Raman signals and allow absolute Raman scattering coefficients to be determined. ? 2010 Society of Photo-Optical Instrumentation Engineers.