Probability distribution variation in high-frequency ultrasound blood echogenicity under in-vitro and in-vivo blood flow

The dynamic phenomena of erythrocyte aggregation (EA) need to be analyzed statistically since EA varies spatially and temporally. In the present study, the cross-sectional B-mode images were acquired from a mock circulatory system with varying blood flow velocity (BFV) under steady flow, and the human radial artery using an ultrasound biomicroscopy system at 20 MHz. The kurtosis (K) and skewness (S) coefficients, and the Nakagami parameter (m) were computed for each image. For the in-vitro experiment, both K and S increased about 0.87±0.18 and 0.63±0.09 with increasing BFV from 12 to 44 cm/s, respectively; while m decreased about 0.90±0.20. In-vivo experimental results also showed that K, S, and m varied during a cycle. When BFV varied from 5 to 15 cm/s during a cardiac cycle, K and S increased about 0.36±0.14 and 0.13±0.06 for subject 1, and 0.60±0.24 and 0.15±0.07 for subject 2, respectively; while m was estimated as large as 4.73±0.14 and 2.74±0.09. The in-vivo results seemed to be consistent with the in-vitro results in the sense that K and S increased with BFV despite large m. This study suggests that the statistical analysis of blood echogenicity can be useful for in-vivo hemorheology and blood characterization.