A HIGH-FREQUENCY CONTINUOUS-WAVE DOPPLER ULTRASOUND SYSTEM FOR THE DETECTION OF BLOOD-FLOW IN THE MICROCIRCULATION

Basic ultrasound physics and several clinical and experimental observa tions suggest that high-frequency Doppler ultrasound (HFD) operating i n the frequency range 20-100 MHz holds the promise of detecting blood flow in the microcirculation. This article describes a directional, co ntinuous-wave (CW), 1- to 200-MHz Doppler ultrasound system. The syste m electronics have a dynamic range of 100 dB, a noise floor of 10 nV a nd a directional isolation of 50 dB. The development of a 40-MHz Doppl er transducer composed of two, 81-mu m-thick, lithium niobate crystals that have been air-backed and transmission-line tuned for maximum sen sitivity is described. This device is used to test the CW Doppler syst em using string and capillary phantoms and in vivo tissue. We show tha t HFD can detect and measure velocities on the order of the blood velo cities found in the capillaries (1 mm/s) and arterioles (5 mm/s) with suitable velocity (50-500 mu m/s) and temporal (20-250 ms) resolutions . In vivo measurements demonstrate that HFD is sensitive to the detect ion of blood flow in small vessels. Copyright (C) 1996 World Federatio n for Ultrasound in Medicine & Biology.