Frequency Domain Diffuse Correlation Spectroscopy: A New Method for Simultaneous Estimation of Static and Dynamic Tissue Optical Properties

Oxygenation and blood flow are important biomarkers of tissue health and they play a vital role in diagnosis and monitoring of diseases in both clinical and basic science research. Diffuse optical instruments offer effective solutions for continuous monitoring of oxygen and blood flow because they are non-invasive, portable and use non-ionizing light. Traditionally, this requires use of two complementary instruments, Diffuse Optical Spectroscopy (DOS) for measuring oxygenation from tissue absorption coefficient (mu(a)) and reduced scattering coefficient (mu(s)') and Diffuse Correlation Spectroscopy (DCS) for measuring blood flow index(F). These hybrid DOS and DCS instruments use collocated sources leading to issues like partial volume effects, increased cost, and size. Here, we propose a novel technique - Frequency Domain Diffuse Correlation Spectroscopy (FD-DCS) to overcome these issues. FD-DCS extends and generalizes DCS measurements to the frequency domain, measures a frequency dependent intensity autocorrelation function, which is fit to a frequency domain solution to the correlation diffusion equation for simultaneous estimation of static and dynamic tissue optical properties. We present experiment results validating the technique in tissue simulating liquid phantoms (intralipid + India ink + water) using a new prototype instrument. Specifically, we compare tissue optical properties of phantoms of different absorption and scattering coefficients measured with FD-DCS and commercial FD-DOS. Our results show successful estimation of mu(a), mu(s) and F with minimal errors.