Real-time volumetric imaging of cells and molecules in deep tissues with Takoyaki ultrasound

Acoustic contrast agents and reporter genes play a critical role in allowing ultrasound to visualize blood flow, map molecules and track cellular function in opaque living organisms. However, existing ultrasound methods to image acoustic contrast agents predominantly focus on 2D planar imaging, while the biological phenomena of interest unfurl in three dimensions. Here, we introduce a method for efficient, dynamic imaging of contrast agents and reporter genes in 3D using multiplexed matrix array transducers. Our "Takoyaki" pulse sequence uses the simultaneous scanning of multiple focal points to excite contrast agents with sufficient acoustic pressure for nonlinear imaging while efficiently covering 3D space. Through in vitro experiments, we first show that the Takoyaki sequence produces highly sensitive volume images of gas vesicle contrast agents and compare its performance with alternative imaging schemes. We then establish its utility in cellular imaging in vivo by visualizing acoustic reporter gene-expressing tumors in a mouse model of glioblastoma. Finally, we demonstrate real-time volumetric imaging by tracking the dynamics of fluid motion in brain ventricles after intraventricular contrast injection. Takoyaki imaging enables a more comprehensive understanding of biological processes by providing spatiotemporal information in 3D within the constraints of accessible multiplexed matrix array systems.