All-Optical Ultrasound Imaging for Guiding Minimally Invasive Cardiovascular Procedures

High-frequency ultrasound imaging can provide exquisite visualizations of tissue to guide minimally invasive cardiovascular procedures. Conventionally, interventional ultrasound imaging devices have used electronic transducers. Recently, all-optical ultrasound (OpUS) has emerged as a new paradigm for performing pulse-echo imaging, using miniature fiber-optic probes. OpUS transducers use pulsed light to generate ultrasound from engineered optically-absorbing coatings via the photoacoustic effect, and ultrasound reflections from tissue are received with optical interferometry. OpUS transducers fabricated with optical fibres enable high performance ultrasound imaging, including broad bandwidths for high spatial resolution, high sensitivity for large penetration depths, and immunity to electromagnetic interference for compatibility with radiofrequency (RF) ablation. Here we provide an overview of recent developments of OpUS technology, spanning our foundational pre-clinical in vivo experiments at the University College London (UCL) [Light: Science & Applications, 6:e17103(2017)] to commercialisation via the newly formed UCL spin-out Echopoint Medical. We highlight a forward-viewing OpUS probe developed by our team that provided unprecedented real-time views of cardiac tissue (depth: 2.5 cm; axial resolution: 64 microns) to guide transseptal crossing, to monitor RF ablation, to perform intracardiac valve imaging, and to enable 3D medical device tracking. Additionally, we present a rotational, side-viewing OpUS probe that enables intraluminal cross-sectional vascular imaging. We also discuss how the next generation of OpUS transducers will enable concurrent structural and molecular imaging with photoacoustic excitation of endogenous chromophores. This new platform for interventional cardiovascular imaging will allow ultrasound imaging to be integrated into a broad range of minimally invasive devices in different clinical contexts.