3D Transcranial Ultrasound Localization Microscopy in the Rat Brain With a Multiplexed Matrix Probe

Objective: Ultrasound Localization Microscopy (ULM) provides images of the microcirculation in-depth in living tissue. However, its implementation in two-dimension is limited by the elevation projection and tedious plane-by-plane acquisition. Volumetric ULM alleviates these issues and can map the vasculature of entire organs in one acquisition with isotropic resolution. However, its optimal implementation requires many independent acquisition channels, leading to complex custom hardware. Methods: In this article, we implemented volumetric ultrasound imaging with a multiplexed 32 x 32 probe driven by a single commercial ultrasound scanner. We propose and compare three different sub-aperture multiplexing combinations for localization microscopy in silico and in vitro with a flow of microbubbles in a canal. Finally, we evaluate the approach for micro-angiography of the rat brain. The "light" combination allows a higher maximal volume rate than the "full" combination while maintaining the field of view and resolution. Results: In the rat brain, 100,000 volumes were acquired within 7 min with a dedicated ultrasound sequence and revealed vessels down to 31 mu m in diameter with flows from 4.3 mm/s to 28.4 mm/s. Conclusion: This work demonstrates the ability to perform a complete angiography with unprecedented resolution in the living rat's brain with a simple and light setup through the intact skull. Significance: We foresee that it might contribute to democratize 3D ULM for both preclinical and clinical studies.