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 utilized, but 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 the imaging field-of-view (depth and width), frame rate, and resolution uniformity. Using Field II, the transmit energy field 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 for each PWT and DWT case, and several cases of PWT and DWT compounding. The amplitude and resolution of the PSFs, and the uniformity (variance) of each of these metrics over the field-of-view, was measured in each case. This framework was then implemented on a Verasonics Vantage-128 (V-128) research scanner for similar analysis on a wire-target phantom to determine objective guidelines for optimized DWT acquisition schemes based on the given speed of sound in the medium, transmit center frequency, aperture width, and desired field-of-view. Results suggest that a DWT scheme provides improved PSF amplitude and resolution uniformity over a broader field-of-view than PWT, with only a slight reduction in resolution with increasing depths.
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