Super-resolution Imaging with a multifrequency large-aperture hemispherical phased array

Abstract

High-resolution imaging of microvasculature is important for diagnostic and therapeutic applications. Here, the utility of a multi-frequency large-aperture hemispherical phased array in the context of vasculature imaging via passive beamforming and super-resolution techniques was explored at various receive frequencies, to investigate the capability of mapping the emissions of lipid coated phase-change nanodroplets flowing through tube phantoms as well as rabbit renal and cerebral vasculatures in-vivo. With super-resolution techniques, the mean lateral (axial) full-width-at-half-maximum image intensity was estimated to be 16 ± 3 (32 ± 6) μm and 7 ± 1 (15 ± 2) μm, corresponding to approximately 1/85 of normal resolution when received with the subarrays at 612 and 1224 kHz, respectively. The mean positional uncertainties were approximately 1/350 (lateral) and 1/180 (axial) of the receive wavelength in water. The renal and cerebral vasculatures of rabbits were partially visualized. A correlation between transmit pulse and nanodroplet vaporization is observed, demonstrating potentials for nanodroplet vaporization modulation and signal-to-noise ratio enhancement. This study demonstrates the feasibility of mapping vaporized nanodroplets with passive beamforming and super-resolution imaging techniques. It may provide means to map complete vasculature pre- or post-treatment with therapeutic focused ultrasound in organs that can be surrounded by the hemispherical array.