Improved image uniformity using optimized diverging-wave acquisition sequence for high frame rate pulse-echo ultrasound

Abstract

Ultrafast pulse-echo ultrasound imaging uses unfocused plane-wave transmit (PWT) or diverging-wave transmit (DWT) wavefronts and coherent compounding for image reconstruction. PWT imaging is more commonly utilizedbut has a limited region of overlapping insonification. This work characterizes the tradeoffs between PWT and DWT, to determine an optimal DWT transmit scheme for given constraints on imaging field of view (depth and width), frame rate, and resolution uniformity. Using Field II, the transmit energy field of a 64-element, 2.75-MHz linear phased array (Verasonics P4-2v) was analyzed for PWT and various active apertures and relative virtual source locations for DWT. This was followed by a Field II calculation and analysis of point-spread functions (PSFs) at many locations in the field (to depth z = 35 mm and x = 20 mm laterally) for each PWT and DWT case, and several cases of PWT and DWT compounding. The amplitude and resolution of the PSF, and the uniformity (variance) of each of these metrics over the field of view, weremeasured in each case. Preliminary results suggest that a DWT scheme provides improved PSF amplitude uniformity over a broader field of view than PWT, with only a slight reduction in lateral resolution at greater depths.