Fast Acoustic Wave Sparsely Activated Localization Microscopy: Ultrasound Super-Resolution Using Plane-Wave Activation of Nanodroplets

Abstract

Localization-based ultrasound super-resolution imaging using microbubble contrast agents and phase-change nanodroplets has been developed to visualize microvascular structures beyond the diffraction limit. However, the long data acquisition time makes the clinical translation more challenging. In this study, fast acoustic wave sparsely activated localization microscopy (fast-AWSALM) was developed to achieve superresolved frames with subsecond temporal resolution, by using low-boiling-point octafluoropropane nanodroplets and high frame rate plane waves for activation, destruction, as well as imaging. Fast-AWSALM was demonstrated on an in vitro microvascular phantom to super-resolve structures that could not be resolved by conventional B-mode imaging. The effects of the temperature and mechanical index on fast-AWSALM were investigated. The experimental results show that subwavelength microstructures as small as 190 µm were resolvable in 200 ms with plane-wave transmission at a center frequency of 3.5 MHz and a pulse repetition frequency of 5000 Hz. This is about a 3.5-fold reduction in point spread function full-width-half-maximum compared to that measured in the conventional B-mode, and two orders of magnitude faster than the recently reported AWSALM under a nonflow/very slow flow situations and other localization-based methods. Just as in AWSALM, fast-AWSALM does not require flow, as is required by current microbubblebased ultrasound super-resolution techniques. In conclusion, this study shows the promise of fast-AWSALM, a super-resolution ultrasound technique using nanodroplets, which can generate super-resolution images in milliseconds and does not require flow.

Assessing Vessel Reconstruction in Ultrasound Localization Microscopy by Maximum Likelihood Estimation of a Zero-Inflated Poisson Model

“…An alternative approach relying on sparse activation of contrast agents is "Acoustic Wave Sparsely Activated Localization Microscopy" (AWSALM) [28], [29], for which shortened acquisition times were demonstrated in vitro. Owing to its resemblance to ULM in detecting events, the MLE could also be used to evaluate the reconstruction degree of this method.…”

Super-Resolution Ultrasound Image Filtering with Machine-Learning to Reduce the Localization Error

“…Localization-based super-resolution ultrasound (SR-US), also known as ultrasound localization microscopy, relies on detection of microbubbles positions with high precision. Although this method is adapted from optical super-resolution microscopy, many studies have contributed to the development of localization-based SR-US imaging using microbubbles [1]- [17] and nanodroplets [18]- [21]. These developments are explained in detail by a recent review [22].…”

Activation and 3D Imaging of Phase-change Nanodroplet Contrast Agents with a 2D Ultrasound Probe

“…Nanodroplets can be selectively activated on demand to provide an ultrasound contrast signal and can be imaged at high frame rates. Low-boilingpoint nanodroplets have been demonstrated for reducing the SR-US acquisition time as they can be activated, destroyed and imaged on a sub-second time scale [27]. Thanks to these advantages, the use of nanodroplets as an echogenic point source for super-resolution imaging is increasing [28]- [30].…”