3D laser optoacoustic ultrasonic imaging system for research in mice (LOUIS-3DM)

In this work we introduce an improved prototype of three-dimensional imaging system that combines optoacoustic tomography (OAT) and laser ultrasound tomography (LUT) to obtain coregistered maps of tissue optical absorption and speed of sound (SoS). The OAT scan is performed by a 360 degree rotation of a mouse with respect to an arc-shaped array of ultrasonic transducers. A Q-switched laser system is used to establish optoacoustic illumination pattern appropriate for deep tissue imaging with a tunable (730-840 nm) output wavelengths operated at 10 Hz pulse repetition rate. A 532 nm wavelength output, being mostly absorbed within a narrow superficial layer of skin, is used to outline the visualized biological object. Broadband laser ultrasound emitters are arranged in another arc pattern and are positioned opposite and orthogonal to the array of transducers. This imaging geometry allows reconstruction of volumes that depict SoS distributions from the measured time of flight data. The reconstructed LUT images can subsequently be employed by an optoacoustic reconstruction algorithm to compensate for acoustic wavefield aberration and thereby improve accuracy of the reconstructed images of the absorbed optical energy. The coregistered OAT-LUT imaging is validated in a phantom and live mouse using a single-slice system prototype.