Simulated capillary blood flow measurement using a nonlinear ultrasonic contrast agent.

This paper proposes a system for measuring slow, small volume blood flow, such as that found in the capillary beds. The method relies on the injection of a strongly nonlinear echocardiographic contrast agent, whose echoes are then analyzed by a modified Doppler process. The contrast agent is necessary to increase the signal-to-clutter ratio from the small blood volume, and to distinguish the blood movement from other moving structures, such as vessel walls or surrounding tissue. The nonlinear properties of this saccharide-based contrast agent are described, as evidenced by experimental evaluation. The contrast agent and signal processing modality are then tested in a blood flow simulator, at velocities as low as 1.5 mm/s, with good results. In addition, an analysis for applying this technique in vivo is presented, accounting for the dynamic and acoustic parameters of the physiological environment. Finally, some specific applications for this method are discussed, including its limitations.