UC Irvine

Our research is aimed at the development of a frequency-domain instrument for conducting non-invasive, real-time, near-infrared, optical tomography of tissue in vivo. Our goal is to reconstruct a spatial map of the optical properties of a strongly scattering medium in a semi-infinite-geometry sampling configuration. Specifically, we focus our attention on the absorption coefficient ((mu) a ) and the reduced scattering coefficient ((mu) s ') of the medium. We have developed a frequency-domain measurement protocol (which we call precalibrated), which permits one to recover the values of (mu) a and (mu) s ' of a uniform tissue-like phantom from a measurement at a single source-detector separation and a single modulation frequency. It requires a preliminary reference measurement on a calibration sample of known optical properties before the measurement on the investigated sample. This approach is in principle rigorous only in macroscopically homogeneous media. We have verified that the equations valid for uniform media can still be applied to yield qualitative information on the optical nature of the inhomogeneity if the effect of macroscopic inhomogeneities on the measured phase and intensity is not too large. In vitro measurements on turbid media containing scattering and absorbing homogeneities, with optical properties very similar to the background medium, gave encouraging results. We plan to implement this measurement protocol in a multisource, multidetector instrument for optical tomography.