Stability of a Bi-disperse Microbubble Population for Advanced Ultrasound Localization Microscopy

Ultrasound Localization Microscopy (ULM) overcomes the conventional diffraction limit by precisely localizing intravenously injected microbubbles (MBs), enabling microscopic resolution imaging of the vascular network. The long acquisition time necessary to accumulate a sufficient amount of MB signals within the (micro-)vascular region of interest hinders ULM clinical applicability. To address this limitation, we propose a novel approach based on a bi-disperse MB population, composed of two distinct monodisperse MB populations. By uncoupling this population, higher overall MB concentrations can be used, thereby reducing acquisition times. Uncoupling is achieved through a signal processing pipeline that exploits the strong nonlinear response of MBs when their resonance frequency matches the transmission frequency. In this study, we evaluate the in vitro stability of the bi-disperse MB population and assess its separability. Our results confirm both the temporal stability and the effective acoustic separation of the bi-disperse MB population, supporting its potential to enhance ULM performance and accelerate its clinical translation.