FOR DETECTING AND IMAGING BLOOD FLOW IN THE MICROCIRCULATION A HIGH FREQUENCY PULSED-WAVE DOPPLER ULTRASOUND SYSTEM

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 pulsedwave 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, suing 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 mds with suitable velocity and temporal resolutions and can detect and measure in vivo bld velocities of less than 5 mds in arterioles with diameters as small as 20 pm and venules as small as 35 pm. Preliminary experiments with high frequency colour Doppler (HFCDj and high frequency power Doppler (HFPD) flow imaging are also presented.