High-frequency 3-D color-flow imaging of the microcirculation

High-frequency (> 20 MHz) ultrasound (US) flow imaging has the potential to be an important too] for assessing microvascular blood flow in superficial tissues noninvasively. In this paper, we describe the development and evaluation of a 3-D US flow imaging system capable of operating at center frequencies in the 20- to 50-MHz range. Flow images are made for tissue volumes of sizes up to 10 mm laterally and 5 mm in depth, permitting a range of scientific and clinical applications. To acquire data sets in a reasonable time, the 2-D sections were derived from data collected with a transducer that was scanning continuously in a direction perpendicular to the beam axis. Due to spectral broadening effects induced by scanning tissue, significant tradeoffs must be made between frame rate, lateral resolution and the minimum detectable blood velocity. 3-D How images were reconstructed with flow data acquired from a series of adjacent planes. The system was evaluated at a center frequency of 50 MHz, using two PVDF transducers with lateral resolutions of 43 urn and 65 mum and axial resolutions of 66 mum to 72 mum, respectively. Velocity ranges were from below 1 mm/s to 25 mm/s. In vivo validation experiments using the mouse ear demonstrated the ability to follow branching patterns of closely spaced microvessels from 30 mum to 100 mum in diameter. Experiments conducted on mouse tumors successfully imaged microvessel morphology in the tumor microcirculation. (E-mail: goetzda@sten. sunnybrook.utoronto.ca) (C) 2003 World Federation for Ultrasound in Medicine Biology.