High frequency 3D flow imaging of the microcirculation

High frequency (>30 MHz) ultrasound 3D flow imaging has the potential to be an important tool for non-invasively assessing microvessel morphology. In this paper we describe the development and evaluation of a 3D flow imaging system capable of operating in the 20-100 MHz range. The acquisition system and signal processing have been designed to detect microvessels with flow velocities from below 1 mm/s to -50 mm/s. Flow images can be made for sizable tissue volumes (tens of mm laterally and -5 mm in depth) in sufficient time to permit a range of scientific and clinical applications. The system was evaluated at a center frequency of 50 MHz using two PVDF transducers (aperture diameters 2.5 mm; f-numbers 1.4 and 2.0) with lateral resolutions of 43 μ and 65 μ, respectively. Axial resolutions ranged from 66 μ to 72 μ. In vivo validation experiments using mouse ears demonstrated the ability to follow branching patterns of closely spaced microvessels from 30 μ to 100 μ in diameter. Experiments conducted on mouse tumors successfully imaged microvessel morphology in the tumor microcirculation