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 (μ_a) and reduced scattering coefficient (μ_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 μ_a and μ_s′ or assumed constant μ_a and μ_s′. Inaccurate μ_s′ assumptions resulted in much greater flow index errors than inaccurate μ_a. Underestimated/overestimated μ_s′ from -35%/+175% lead to flow index errors of +110%/-80%, whereas underestimated/overestimated μ_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 μ_a and μ_s′ changes should concurrently measure flow index and optical properties for accurate extraction of blood flow information.