Cardiac Labeling of Phase-Change Nanodroplets Enables Contrast-Controllable Super-Resolution Ultrasound.

OBJECTIVE: Microbubble concentration control is crucial for enhancing the quality and efficiency of super-resolution ultrasound (SRUS) imaging. However, contrast-enhanced ultrasound typically employs a microbubble bolus injection, where the regulation of microbubble concentration is limited. In contrast to microbubbles, phase-change nanodroplets (PCNDs) can be selectively activated in both spatial and temporal domains by an acoustic beam. Therefore, this study aimed to investigate the performance of PCNDs in regulating microbubble concentration for SRUS imaging.

METHODS: This study proposed a cardiac-labeling SRUS strategy based on PCNDs with two identical transducers at a center frequency of 18 MHz. The first transducer (Trans #1) was placed over the left ventricle of a mouse and used a custom pulse sequence to activate the PCNDs, while the second transducer (Trans #2) performed ultrafast plane wave imaging at 600 Hz on the target site after activation for SRUS imaging.

RESULTS: In vivo results showed that the custom pulse sequence successfully activated PCNDs in the left ventricle. With the coordination of both transducers, SRUS imaging of the target site was achieved. The microbubble concentration could be effectively controlled by adjusting the activation voltage of Trans #1 within the 30-40V range.

CONCLUSION: The proposed strategy was validated in a mouse model using dual transducers, demonstrating feasibility and repeatability, and offering a solid technical basis for high-quality, rapid SRUS imaging of diverse organs.