Fast-AWSALM – Real Time Ultrasound Super-Resolution with Plane-Wave Activation of Nanodroplets

G. Zhang, S. Harput, H. Hu, K. Christensen-Jeffries, J. Zhu, J. Brown, C. H. Leow, R. J. Eckersley, C. Dunsby, and M.X. Tang, “Fast Acoustic Wave Sparsely Activated Localization Microscopy (fast-AWSALM): Ultrasound Super-Resolution using Plane-Wave Activation of Nanodroplets

Accetped by UFFC


G. Zhang, S. Harput, H. Hu, J. Zhu, C. H. Leow, and M.-X. Tang are with the Ultrasound Laboratory for Imaging and Sensing Group, Department of Bioengineering, Imperial College London, London, SW7 2AZ, U.K. (email:

K. Christensen-Jeffries, J. Brown, and R. J. Eckersley are with the Division of Imaging Sciences, Biomedical Engineering Department, King’s College   London, London, SE1 7EH, U.K.

C. Dunsby is with the Department of Physics and the Centre for Pathology,   Imperial College London, London, SW7 2AZ, U.K.


Localization-based ultrasound super-resolution imaging using microbubble contrast agents and phase-change nano-droplets 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 super-resolved frames with sub-second 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 was investigated. Experimental results show that sub-wavelength micro-structures 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 conventional B-mode, and two orders of magnitude faster than the recently reported AWSALM under a non-flow/very slow flow situations and other localization based methods. Just as in AWSALM, fast-AWSALM does not require flow, as is required by current microbubble based 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 milli-seconds and does not require flow.

Supporting Bodies:

The research was partially funded by the UK EPSRC under Grants EP/N015487/1, EP/N014855/1 and EP/M011933/1, and the CRUK Multidisciplinary Project Award (C53470/A22353).

Figure. (a-c) show the summation of 1000 conventional B-mode images. (d-f) show the summation of the corresponding SVD-filtered images. (g-i) show the final super-resolution images for water (a, d, g), microbubble (b, e, h), nanodroplet (c, f, i) experiments respectively. (j) and (k) show the larger version of two final super-resolution images for microbubble and nanodroplet experiments respectively.

Figure. (a) Conventional B-mode image (b) SVD-filtered image (c) super-resolution image (d) optical image of the 200 µm cross-tube phantom. (e) and (f) show the resolution measurements at different lateral ROIs indicated by the red lines on the images. The scale bar in the optical image is 5mm.

The video shows B-mode, singular value decomposition (SVD)-filtered, and super-resolution images of water, microbubbles and nanodroplets within the 200-um crossed-tube phantom respectively.