  Super-Resolution Ultrasound (SRUS) through localizing spatially isolated
microbubbles has been demonstrated to overcome the wave diffraction limit and
reveal the microvascular structure and flow information at the microscopic
scale. However, 3D SRUS imaging remains a challenge due to the fabrication and
computational complexity of 2D matrix array probes and connections. Inspired by
X-ray radiography which can present volumetric information in a single
projection image with much simpler hardware than X-ray CT, this study
investigates the feasibility of volumetric image projection super-resolution
(VIP-SR) ultrasound using a 1D unfocused linear array. Both simulation and
experiments were conducted on 3D microvessel phantoms using a 1D linear array
with or without an elevational focus, and a 2D matrix array as the reference.
Results show that, VIP-SR, using an unfocused 1D array probe can capture
significantly more volumetric information than the conventional 1D elevational
focused probe. Compared with the 2D projection image of the full 3D SRUS
results using the 2D array probe with the same aperture size, VIP-SR has
similar volumetric coverage using 32 folds less independent elements. The
impact of bubble concentration and vascular density on the VIP-SR US was also
investigated. This study demonstrates the ability of high-resolution volumetric
imaging of microvascular structures at significantly reduced costs with VIP-SR.
