In the last twenty years, the progressive introduction of plane or diverging ultrasonic wave transmissions rather than line by line scanning focused beams broke the resolution limits of ultrasound imaging. By using such large field of view transmissions, the frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can be provided typically in tens of micro-seconds (several thousands of frames per second). Interestingly, this leap in frame rate is not only a technological breakthrough but it permits the advent of completely new ultrasound imaging modes, including shear wave elastography1-2, electromechanical wave imaging, ultrafast Doppler, ultrafast contrast imaging, and even functional ultrasound imaging (fUS imaging) of brain activity introducing Ultrasound as an emerging full-fledged neuroimaging modality.

At ultrafast frame rates, it becomes possible to track in real time the transient vibrations – known as shear waves – propagating through organs. Such "human body seismology" provides quantitative maps of local tissue stiffness whose added value for diagnosis has been recently demonstrated in many fields of radiology (breast, prostate and liver cancer, cardiovascular imaging, ...).

For blood flow imaging, ultrafast Doppler permits high-precision characterization of complex vascular and cardiac flows. It also gives ultrasound the ability to detect very subtle blood flow in very small vessels. In the brain, such ultrasensitive Doppler paves the way for fUltrasound or fUS (functional ultrasound) imaging of brain activity with unprecedented spatial and temporal resolution compared to fMRI. It provides the first modality for imaging of the whole brain activity working on awake and freely moving animals with unprecedented resolutions 3-6 and was also translated recently to clinics7-8.

Finally, we recently demonstrated that it can be combined with 3 µm diameter microbubbles injections in order to provide a first in vivo and non-invasive imaging modality at microscopic scales deep into organs combined with contrast agents by localizing the position of millions of microbubbles at ultrafast frame rates.

This ultrasound localization microscopy technique solves for the first time the problem of in vivo imaging at microscopic scale the whole brain vasculature 9. Beyond fundamental neuroscience or stroke diagnosis, it will certainly provide new insights in the understanding of tumor angiogenesis, for example combined with PET/CT imaging10.

1. M. Tanter and M. Fink, Ultrafast Imaging in Biomedical Ultrasound, IEEE UFFC, 61(1), pp. 102-119, 2014
2. M.E. Fernandez-Sanchez et al, Nature, July 2015
3. Mace et al., Nature Methods, Jun. 2011
4. Osmanski et al, Nature Comm., Oct. 2014
5. L.A. Sieu et al, Nature Methods, Jul. 2015
6. Bergel et al, Nature Comm., in press 2018
7. Imbault et al, Scientific Reports 2017
8. Demene et al, Science Translational Medicine, 2017
9. C.Errico et al, Nature, Dec. 2015
10. Provost et al, Nature Biomedical Engineering, Feb. 2018