Over the past several decades, OCT has been developed as a non-invasive imaging technique that provide high-resolution, depth-resolved cross-sectional images of highly scattering samples such as biology. The visualization of internal blood flow in biological tissue is one of the main directions of OCT. Optical coherence tomography angiography (OCTA) [1], [2], [3] was then proposed in which in a short interval, data are obtained by repeating multiple scans at each spatial location, and the signal amplitude, phase, and complex value will change within the time interval. The blood flow signals can be distinguished by analyzing properties of these changes. Currently, common OCTA algorithms include speckle variance (SVOCT) [4], phase variance (PVOCT) [5], [6] ,correlation mapping (cmOCT) [7], [8], optical micro-angiography (OMAG) [9].

Apart from the visualization of blood vessels, the quantification of blood flow information is also significant in clinical diagnosis. Blood flow velocity is one of the important parameters, which plays an important role in the diagnosis and treatment of retinal diseases [10] and neurological diseases [11]. There are many methods to measure the flow velocity. For instance, OCT based on the Doppler effect(DOCT) [12], polarization multiplexing [13], delay multiplexing [14], multiplexing light source [15], and additional OCT interferometers [16]. Moreover, in a previous study, the slope of the normalized intensity autocorrelation function was found to be proportional to the transverse velocity of an Intralipid flow phantom [17].

In addition to flow velocity, another important parameter of blood is hematocrit(HCT), that is, the percentage of red blood cells in the whole blood volume. For example, polycythemia vera increases the HCT value while anemia reduces the HCT value, and the complications or mortality after cardiac surgery are related to the HCT value [18], [19]. However, in many cases, the concentration of red blood cells in blood is often difficult to measure by non-invasive methods. The basic principle of OCT is that the low-coherence light source is incident on a biological sample to produce backscattered light, which interferes with the reference light, to obtain the internal information of the biological sample. The particles with scattering properties in the blood are mainly red blood cells. Therefore, theoretically, changes in HCT will be reflected in OCT signals. For instance, Lee et al.. found that when particle concentration changes, the OCT signal has a corresponding change trend in the depth direction through phantom experiments [20]. The scattering coefficients of solutions with different concentrations will be different [21]. Wang et al.. analyzed the relationship between temporal statistics characteristics and concentration of low-concentration solution based on Brownian motion. Through experiments, it was proved that the probability density distribution of the solution was independent of the flow velocity of the solution [22].

The above reference all use phantom experiments to explore the relationship between solution concentration and scattering coefficient or temporal statistical characteristics. Due to the complexity of blood components, it is more complicated to explore the relationship between blood concentration and scattering coefficient, temporal statistical characteristics than phantom experiments. Based on this, this paper explores the relationship between the OCT signal’s intensity and the statistical characteristics of solution with different concentrations in more detail. The corresponding probability density distribution curves were obtained by using the structural information of OCT. Four parameters of the curves: intercept, peak amplitude, peak count, and FWHM are defined to explore the relationship between them and solution concentration. Our results show that the statistical characteristics of the OCT signal are concentration-dependent and depth-dependent. What’s more, through in vivo skin experiments, it is found that the statistical properties of human skin also have a depth dependence,but less correlated with Intralipid solution.