Aberrating Murine Skull Microvascular Phantom for Super-Resolution Ultrasound Imaging

Microvascular phantoms are the primary experimental method for evaluating the performance of super-resolution ultrasound (SRUS) imaging. Typically, microvascular phantoms have consisted of simple microchannels embedded in homogenous tissue-mimicking materials (TMM). However, these phantoms limit the performance evaluation of SRUS under realistic conditions as they lack characteristics of in vivo vascular tissue. Previously, a novel method of fabricating optically validated microvascular phantoms with circular cross-section vessels, branching and variable microvascular density has been demonstrated using polydimethylsiloxane (PDMS) as the embedding material. In this work, we present an improved microvascular phantom, with superior tissue mimicking characteristics, as well as heterogeneity in the supporting matrix. The phantom consists of a bifurcating vessel surrounded by an ex vivo murine skull, and embedded in polyurethane. The acoustic properties of the new TMM can be modified by adding a softening agent to obtain a longitudinal wave speed from 1350 to 1364 m/s and an acoustic attenuation from -4.8 to -8.1 dB/cm (measured at 3 MHz). The murine skull provided aberration and bone-shadowing effects that were noticeable in the SRUS results. The SRUS localisation densities in and out of the murine skull were compared, and it was observed that the skull drastically reduced the microbubble count when compared to the ones localised outside of it.