Ultrasensitive ultrasound imaging of gene expression with signal unmixing

Abstract

Acoustic reporter genes (ARGs) that encode air-filled gas vesicles enable ultrasound-based imaging of gene expression in genetically modified bacteria and mammalian cells, facilitating the study of cellular function in deep tissues. Despite the promise of this technology for biological research and potential clinical applications, the sensitivity with which ARG-expressing cells can be visualized is currently limited. Here we present burst ultrasound reconstructed with signal templates (BURST)-an ARG imaging paradigm that improves the cellular detection limit by more than 1,000-fold compared to conventional methods. BURST takes advantage of the unique temporal signal pattern produced by gas vesicles as they collapse under acoustic pressure above a threshold defined by the ARG. By extracting the unique pattern of this signal from total scattering, BURST boosts the sensitivity of ultrasound to image ARG-expressing cells, as demonstrated in vitro and in vivo in the mouse gastrointestinal tract and liver. Furthermore, in dilute cell suspensions, BURST imaging enables the detection of gene expression in individual bacteria and mammalian cells. The resulting abilities of BURST expand the potential use of ultrasound for non-invasive imaging of cellular functions.