QUANTITATIVE-DETERMINATION OF THE ABSORPTION-SPECTRA OF CHROMOPHORES IN STRONGLY SCATTERING MEDIA - A LIGHT-EMITTING-DIODE BASED TECHNIQUE

The absorption and scattering coefficient of a macroscopically homogen eous strongly scattering medium (lipid emulsion) containing Methylene Blue is quantitatively measured in the spectral range from 620 to 700 nm. We conduct the measurements in the frequency domain by using a lig ht-emitting diode (LED) whose intensity is modulated at a frequency of 60 MHz. We derive an analytical expression for the absorption and sca ttering coefficients that is based on a two-distance measurement techn ique. A comparison with other measurement protocols such as measuremen t at two modulation frequencies shows that the two-distance method giv es a better determination of the scattering and absorption coefficient s. This study highlights the efficiency and ease of use of the LED tec hnique, which lends itself to in vivo spectroscopy of biological tissu es.