Effects of Aberration on Super-Resolution Ultrasound Imaging Using Microbubbles: A Simulation Study

Super-resolution ultrasound (SRUS) can overcome the conventional ultrasound diffraction limit to uncover microvascular structure and flow at depths not possible with existing imaging modalities. However, the resolution limit of SRUS depends on image quality. Phase aberration, reverberation and multiple scattering caused by varying tissue layers cause image degradation. This is likely to significantly impact SRUS imaging depths, potentially reaching several centimeters. Here, we investigate the effect of aberration on SRUS in soft tissues using 2D simulations. B-Mode and pulse inversion (PI) acquisitions of transabdominal contrast-enhanced data at 50 mm depth were simulated using k-Wave. The Marmottant model was used to simulate responses from microbubbles of varying position and size. Results indicate SRUS localization errors increased in both the lateral and axial direction with increasing aberration and were affected by both the imaging mode and microbubble size, even under control conditions. Average localization errors reached over $800~\mu $ m axially for both B-Mode and PI using cross-correlation localization methods. Furthermore, PI was able to detect approximately 10% more signals from microbubbles than with B-Mode imaging. The scale of these errors relative to micro-vascular structures of interest suggests that aberration, as well as the imaging and localization method, will have a considerable impact on SRUS performance and require attention to ensure its success.