Compressed optoacoustic data acquisition based on a cluster of acoustic scatterers

Abstract

A myriad of optoacoustic imaging systems based on scanning focused ultrasound transducers or on tomographic acquisition of pressure signals are available. In all cases, image formation is based on the assumption that ultrasound waves undergo no distortion and propagate with constant velocity across the sample and coupling medium (typically water). Thereby, ultrasound time-of-flight readings from multiple time-resolved signals are required to form an image. Acoustic scattering is known to cause distortion in the signals and is generally to be avoided. In this work, we exploit acoustic scattering to physically encode the position of optical absorbers in the acquired time-resolved signals and hence reduce the amount of data required to reconstruct an image. This new approach was experimentally tested with an array of cylindrically-focused transducers, where a cluster of acoustic scatterers was introduced in the ultrasound propagating path between the sample and the array elements. Ultrasound transmission was calibrated by raster scanning a lightabsorbing particle across the effective field of view. The acquired calibrating signals were then used for the development of a regularized model-based iterative algorithm that enabled reconstructing an image from a relatively low number of optoacoustic signals. A relatively short acquisition time window was needed to capture the entire optoacoustic field, which demonstrates the high signal compression efficiency. The feasibility to form an image with a relatively low number of signals is expected to play a major role in the development of a new generation of optoacoustic imaging systems.