Minimization of Nanodroplet Activation Time using Focused-Pulses for Droplet-Based Ultrasound Super-Resolution Imaging

One of the crucial challenges in the application of ultrasound super-resolution imaging using microbubble contrast agents to the clinic is the long acquisition time. Recently acoustic wave sparsely activated localization microscopy (AWSALM) was developed to activate, image, and destroy nanodroplets to achieve ultrasound super-resolution imaging. The activation and destruction of nanodroplets using focused pulses in AWSALM can generate new localization signals without relying on flow and shows the potential to achieve faster ultrasound super-resolution. However, the technique requires optimization to achieve good activation efficiency with the minimum amount of activation time.This work investigates how the different activation strategies affect the activation time and efficiency. A range of activation sequences with different F-numbers and spacing between transmit foci are used and their activation efficiency and the data acquisition time are quantified. The results show that sweeping the focus of the activation pulse with an F-number of 0.4 and a step size of 2.5 wavelengths can generate the highest droplet activation. By using a larger or smaller spacing between consecutive focused activation beams generated lower contrast, which suggests that densely spaced activation pulses may destroy the activated nanodroplets generated by the previous activation pulse. In summary, this study demonstrates that the rate of activation of nanodroplets can be increased by optimizing the F-number and the sweep step size. This finding can inform the development of droplet-based super-resolution imaging to further minimize the data acquisition time.