Although the use of ultrasonic plane-wave transmissions rather than line-per-line focused beam transmissions has been long studied in research, clinical application of this technology was only recently made possible through developments in graphical processing unit (GPU)-based platforms. Far beyond a technological breakthrough, the use of plane or diverging wave transmissions enables attainment of ultrafast frame rates (typically faster than 1000 frames per second) over a large field of view. This concept has also inspired the emergence of completely novel imaging modes which are valuable for ultrasound-based screening, diagnosis, and therapeutic monitoring. In this review article, we present the basic principles and implementation of ultrafast imaging. In particular, present and future applications of ultrafast imaging in biomedical ultrasound are illustrated and discussed.

. Relative to fMRI, it has much faster temporal dynamics (ms rather than seconds), substantially higher spatial resolution (100µm rather than millimeters), lower cost, and greater portability. However, most fUS studies thus far have investigated its sensitivity in capturing coarse-grained sensory responses [3][4][5] , or used it to explore indirect inplane brain connectivity 6,7 . Here, we pushed the limits of fUS imaging to demonstrate its 35 capability in capturing a fine-grained functional characterization of sensory systems and direct, long-distance connectivity scheme between brain structures. We show that fUS . CC-BY-NC-ND 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/249417 doi: bioRxiv preprint first posted online Jan. 17, 2018; 2 imaging can rapidly produce highly-resolved 3D maps of responses reflecting precise tonotopic organizations of the vascular system in the almost complete auditory pathway of awake ferrets. We further demonstrate that fUS imaging can provide voxel to voxel 40 independent information (100µm), indicative of its extreme sensitivity and spatial functional resolution. These measurements are conducted over several days in small (1-2mm 3 size) and deep nuclei (8mm below the cortical surface), as well as across various fields of the auditory cortex. On a broader scale, we describe how fUS can be used to assess long distance (out-of-plane) connectivity, with a study of top-down projections from frontal cortex 45 to the auditory cortex. Therefore, fUS can provide a multi-scale functional mapping of a sensory system, from the functional properties of highly-resolved single voxels, to inter-area functional connectivity patterns. Results and discussion 50Physiological experiments were conducted in 3 awake ferrets (Mustela putorius furo, thereafter called V, B and S). After performing craniotomies over the temporal lobe, chronic imaging chambers were installed (both hemispheres in one animal, and right hemispheres in the other two) to access a large portion of both the auditory (middle and posterior ectosylvian gyri -resp. MEG and PEG) and visual cortex (in caudal suprasylvian and lateral gyri) ( In order to reveal the tonotopic organization of the auditory structures, we recorded in each voxel the evoked hemodynamic responses to pure tones of 5 different frequencies, and then computed the resultant 3-dimensional tonotopic map (Fig. 1c-e, Figure 1-figure supplement 2). Within a relatively short time (10 to 15 minutes per slice), we could 65 accurately reproduce the known tonotopic organization of the primary (A1, MEG) and secondary auditory cortex (PEG), with a high-to low-frequency gradient in A1, reversing to a low-to high-frequency gradient in the dorsal PEG (Fig. 1c). We note that the fUS enabled us to map within the challenging deep folds of the ferret auditory cortex, such as the supr...

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The feasibility of temperature estimation during high-intensity focused ultrasound therapy using pulseecho diagnostic ultrasound data has been demonstrated. This method is based upon the measurement of thermallyinduced modifications in backscattered RF echoes due to thermal expansion and local changes in the speed of sound. It has been shown that strong ripple artifacts due to the thermo-acoustic lens effect severely corrupt the temperature estimates behind the heated region. We propose here a new imaging technique that improves the temperature estimation behind the heated region and reduces the variance of the temperature estimates in the entire image. We replaced the conventional beamforming on transmit with multiple steered plane wave insonifications using several subapertures. A two-dimensional temperature map is estimated from axial displacement maps between consecutive RF images of identically steered plane wave insonifications. Temperature estimation is then improved by averaging the two-dimensional maps from the multiple steered plane wave insonifications. Experiments were conducted in a tissuemimicking gelatin-based phantom and in fresh bovine liver.