A high frequency continuous-wave Doppler ultrasound system for detection of blood flow in the microcirculation

Basic ultrasound physics and several clinical and experimental observations suggest that high frequency Doppler ultrasound (HFD) operating in the frequency range 20 to 100 MHz holds the promise of a real-time, non-invasive, depth-resolving technique capable of detecting blood flow in the microcirculation with suitable spatial and temporal resolutions. This paper describes a directional, continuous-wave, high frequency Doppler ultrasound (CW HFD) system which we have developed and optimised for use in an investigation to quantify HFD's abilities. The system electronics operates over the frequency range 1 to 200 MHz and has a dynamic range of 100 dB and a noise floor of 10 nV. Using a string phantom and a sensitive 40 MHz transducer we show that HFD can detect and measure velocities of the order of 1 mm/s, the velocity of blood in a capillary. Also, using in vivo measurements we demonstrate that HFD is sensitive to the detection of blood flow in small vessels.