Ultrasound: An Unexplored Tool for Blood Flow Visualization and Hemodynamic Measurements

Ultrasonic scattering by blood has been studied both theoretically and experimentally for a better characterization of the performance of ultrasonic devices. In the course of these investigations it became clear that ultrasonic scattering from blood is critically related to the hematological and hemodynamic properties of blood, including hematocrit, plasma protein concentration, flow rate, and flow cycle duration, to name a few parameters. An unexpected conclusion from this work is that ultrasound appears to be a totally unexplored and ignored tool for blood flow visualization and hemodynamic measurements. Two unique hemodynamic phenomena have been observed: the black hole, a low echogenic zone in the center stream of a blood vessel, and the collapsing ring, an hyperechogenic ring converging from the vessel periphery toward the center, and eventually collapsing during pulsatile flow. They seemed to be resulted from the spatial and temporal variations of the shear rate and acceleration in the vessel.