Optical probe and frequency-domain instrumentation to study spatial and temporal correlations of fluctuations in tissues

We have used Photon Density Wave Fluctuation Correlation Spectroscopy (PDW-FCS) to study spatial and temporal correlations of large-scale (~1 mm) optical fluctuations in turbid media such as tissues. Our method uses high frequency (110 MHz) intensity modulated near-infrared light traveling in multiply scattering media. We measure the power spectra of the average value (DC), modulation amplitude (AC) and phase (Φ) of the photon density wave launched in the turbid medium. We have designed an optical probe, consisting of two source-detector pairs, which in conjunction with a correlation algorithm restricts the region probed by the photon density wave.