Imagine being able to study the human brain in real-world scenarios while the subject displays natural behaviors such as locomotion, social interaction, or spatial navigation. The advent of ultrafast ultrasound imaging brings us closer to this goal with functional ultrasound imaging (fUSi), a mobile neuroimaging technique. Here, we present real-time fUSi monitoring of brain activity during walking in a subject with a clinically approved sonolucent skull implant. Our approach uses personalized 3D-printed fUSi helmets for stability, optical tracking for cross-modal validation with functional magnetic resonance imaging, advanced signal processing to estimate hemodynamic responses, and facial tracking of a lick licking paradigm. These combined efforts allowed us to show consistent fUSi signals over 20 months, even during high motion activities such as walking. These results demonstrate the feasibility of fUSi for monitoring brain activity in real-world contexts, marking an important milestone for fUSi-based insights in clinical and neuroscientific research.

Power Doppler (PD) imaging has become a staple in high frame rate ultrasound imaging due to its ability to image small vessels and slow-moving flows, such as in the case of imaging blood flow in the brain. Alternatively, color Doppler (CD) can be used to determine the one-dimensional directional information of the blood scatterers. This can help determine if the flow is arterial or venous, or distinguish between adjacent flows that have an opposite direction. Current methods for estimating 2D blood velocity vectors rely mostly on trigonometric solutions using synthetic apertures or, large plane-wave angles in transmission and sub-apertures in receive to be able to resolve the 2D vector. Relative to PD or CD techniques, these methods are more computationally expensive and have not been successfully used to image blood flow direction within micrometer sized vasculature. In this paper, we propose to use the orientations of the vessels derived from a directional spatial filter in combination with the CD signal to enhance the PD images with directional information. This approach was tested on simulated data as well as on a 2D image containing brain vasculature of a mouse.