The effects of hematocrit, shear rate, and turbulence on ultrasonic Doppler spectrum from blood.

Previous studies of ultrasonic scattering properties of blood using a pulse-echo experimental arrangement show that ultrasonic backscatter from blood is influenced by a number of factors including hematocrit, shear rate, and the nature of flow (J. Acoust. Soc. Amer., vol. 75, p. 1265, 1984 and J. Acoust. Soc. Amer., vol. 84, p. 1, 1988). Since the Doppler frequency spectrum from a Doppler flowmeter is derived from echoes backscattered by red blood cells in the flowing blood, it is also undoubtedly a function of these parameters. The effects of these parameters on Doppler spectrum from blood have been investigated using a pulsed Doppler flowmeter. The results agree well with those obtained in previous studies. One important conclusion of this study is that the assumption that the Doppler spectral power density at a frequency in Doppler spectrum is linearly proportional to the number of red cells flowing at that velocity used in many theoretical models developed to explain the Doppler phenomenon may be erroneous. An alternative is proposed. It is shown that conclusions derived from these theoretical models would remain valid by making this assumption.