Functional ultrasound localization microscopy in the murine brain: Challenges and new techniques

Functional ultrasound localization microscopy (fULM) is a new technique that combines the principles of ULM and functional ultrasound (fUS) to achieve brain-wide and micrometer-scale mapping of brain neural activities based on neurovascular coupling. The unique combination of high imaging spatial resolution, large imaging field-of-view, and deep imaging depth of penetration makes fULM a potentially transformative technology for numerous neuroscience applications where activities from both global neural networks and local neurocircuits need to be recorded simultaneously and continuously. At present, however, fULM suffers from many technical and pragmatic challenges, including low sensitivity and specificity to neural activities, the need of long data acquisition with continuous infusion of microbubbles and repeated simulations, and the lack of viable 3D imaging solutions that are essential for neuroscience research. In this presentation, I will first introduce the principles and technical challenges of fULM, followed by recent advances achieved by our group including (1) enhanced microbubble localization, tracking, and other post-processing techniques to boost fULM’s sensitivity to neural activities; (2) 3D fULM based on 2D matrix arrays that are compatible with mainstream 256-channel ultrasound systems; and (3) an awake fULM imaging platform for mice and rats that allows whole-brain, microscopic-scale recording of functional neural activities in awake animals.