All-optical in vivo photoacoustic tomography by adaptive multilayer acoustic backpropagation

Abstract

Abstract Photoacoustic imaging offers both high optical contrast and substantial imaging depth, serving as a robust tool for diverse biological and medical applications. While piezoelectric ultrasound transducers have traditionally been employed for acoustic pressure measurements and array-based configurations have enabled high-speed volumetric imaging. However, these approaches often require physical contact with the specimen under imaging and face limitations in spatial sampling bandwidth. To address these challenges, we present an all-optical photoacoustic imaging technique designed for high-resolution volumetric imaging of objects embedded within optically thick scattering media. Utilizing a soft cover layer and employing coherent averaging, our system enables optical profiling of nanometer-scale surface displacements caused by photoacoustic waves with subwavelength spatial sampling, even on complex and dynamically fluctuating biological surfaces. Furthermore, we introduce an adaptive multilayer acoustic backpropagation algorithm for high-resolution image reconstruction. This algorithm offers in situ adjustment of acoustic velocities across different media, compensating for the impedance mismatch between the tissue and the cover layer. The system achieves imaging up to a depth of 5 mm, with lateral and axial resolutions of 158 µm and 92 µm, respectively. We demonstrate in vivo volumetric imaging of the vasculature of a mouse's hindlimb as well as the blood vessels of a chicken embryo.