A high frequency pulsed-wave Doppler ultrasound system for detecting and imaging blood flow in the microcirculation

Previous work with a 40 MHz continuous-wave Doppler ultrasound system has demonstrated the potential of high frequency Doppler ultrasound (HFD) operating in the frequency range 20 to 100 MHz to detect blood flow in the microcirculation. This paper describes a directional, pulsed-wave Doppler ultrasound (PW HFD) system designed and constructed to further investigate this potential. The PW HFD system electronics have a dynamic range of 80 dB, a noise floor of 250 nV, a directional isolation of 45 dB and operate over the frequency range 1 to 200 MHz. Tests of the system with a focused 50 MHz PVDF transducer, string phantom and in vivo tissue have demonstrated that the PW HFD system is capable of detecting and measuring velocities on the order of 0.5 mm/s with suitable velocity and temporal resolutions and can detect and measure in vivo blood velocities of less than 5 mm/s in arterioles with diameters as small as 20 /spl mu/m and venules as small as 35 /spl mu/m. Preliminary experiments with high frequency colour Doppler (HFCD) and high frequency power Doppler (HFPD) flow imaging are also presented.