Chemometric analysis of frequency-domain photon migration data: quantitative measurements of optical properties and chromophore concentrations in multicomponent turbid media

Frequency-domain photon migration (FDPM) is a widely used technique for mea suring the optical properties (i.e., absorption, mu(a), and reduced scatter ing, mu(s)', coefficients) of turbid samples. Typically, FDPM data analysis is performed with models based on a photon diffusion equation; however, an alytical solutions are difficult to obtain for many realistic geometries. H ere, we describe the use of models based instead on representative samples and multivariate calibration (chemometrics). FDPM data at seven wavelengths (ranging from 674 to 956 nm) and multiple modulation frequencies (ranging from 50 to 600 MHz) were gathered from turbid samples containing mixtures o f three absorbing dyes. Values for mu(a) and mu(s)' were extracted from the FDPM data in different ways, first with the diffusion theory and then with the chemometric technique of partial least squares. Dye concentrations wer e determined from the FDPM data by three methods, first by least-squares hi s to the diffusion results and then by two chemometric approaches. The accu racy of the chemometric predictions was comparable or superior for all thre e dyes. Our results indicate that chemometrics can recover optical properti es and dye concentrations from the frequency-dependent behavior of photon d ensity waves, without the need for diffusion-based models. Future applicati ons to more complicated geometries, lower-scattering samples, and simpler F DPM instrumentation are discussed. (C) 2000 Optical Society of America.