A feasibility study on the determination of blood hematocrit with Nakagami parameter calculated from backscattered signals

The feasibility of quantifying various hematocrits using the Nakagami parameter was evaluated in this study. The ultrasonic signals backscattered from red cell suspensions with hematocrits ranging from 3% to 50% were collected using a 5 MHz focused transducer. The Hilbert transform and logarithmic compression were in turn applied to the backscattered signals to obtain the uncompressed and compressed envelopes for estimating the Nakagami model parameter. The Nakagami parameter calculated using the uncompressed backscattered envelopes cannot be used to separate various hematocrits due to that the probability distributions of the uncompressed envelopes of different hematocrits all follow Rayleigh statistics, as indicated by their near-unity Nakagami parameters. In contrast, all of the compressed backscattered envelopes tended to be post-Rayleigh distributions, further making the corresponding Nakagami parameters dependent on the hematocrit, in which the mean parameter increased from 7.2 to 8.04 with the hematocrit from 3% to 12%. As the hematocrits were increased from 12% to 50%, the corresponding Nakagami parameter decreased from 8.04 to 5.77. This demonstrates that different hematocrits can be effectively distinguished using the Nakagami parameter after applying logarithmic compression to the envelope signals. Since it is not affected by the system gain and dynamic range, the Nakagami parameter estimated from compressed backscattered envelopes might be a useful parameter for the future development of the real-time examinations of the hematocrit by ultrasound technique.