Estimation of the Signal-to-Noise Ratio in Incoherent Optical Fluctuation Flowmetry

Incoherent Optical Fluctuation Flowmetry (IOFF) is an optical technique for assessing tissue blood flow (BF). This technique is based on the spectral analysis of low-frequency fluctuations in the registered optical signal caused by blood volume changes inside a tissue. The technique can be realized using an optical probe with LEDs. The aim of this study was to evaluate the signal-to-noise ratio (SNR) in IOFF as a function of the distance between a LED and a detector. For this, we developed an experimental setup with a variable source-detector separation. The measurements were carried out on 5 healthy volunteers at the wavelength of 810 and at distances of 4, 6, 8 and 10 mm. To obtain a useful signal, we used the spectral approach to remove noise. The best signals were obtained at a distance of 10 mm (SNR median is 63). Good quality signals were also obtained at distances of 6 and 8 mm (SNR medians are 49 and 55, respectively). It was found that calculated BF is directly proportional to the source-detector separation. As one of the options for standardization of measurements, it was proposed to normalize the output value of BF to a distance.