Influences of tissue absorption and scattering on diffuse correlation spectroscopy blood flow measurements

In this study we evaluate the influences of optical property assumptions on near-infrared diffuse correlation spectroscopy (DCS) flow index measurements. The optical properties, absorption coefficient (mu(a)) and reduced scattering coefficient (mu(s)'), are independently varied using liquid phantoms and measured concurrently with the flow index using a hybrid optical system combining a dual-wavelength DCS flow device with a commercial frequency-domain tissue-oximeter. DCS flow indices are calculated at two wavelengths (785 and 830 nm) using measured mu(a) and mu(s)' or assumed constant mu(a) and mu(s)'. Inaccurate mu(s)' assumptions resulted in much greater flow index errors than inaccurate mu(a). Underestimated/overestimated mu(s)' from -35%/+175% lead to flow index errors of +110%/-80%, whereas underestimated/overestimated mu(a) from -40%/+150% lead to -20%/+40%, regardless of the wavelengths used. Examination of a clinical study involving human head and neck tumors indicates up to +280% flow index errors resulted from inter-patient optical property variations. These findings suggest that studies involving significant mu(a) and mu(s)' changes should concurrently measure flow index and optical properties for accurate extraction of blood flow information. (C) 2011 Optical Society of America