A photoacoustic microscopy system using MEMS and fibre tip transducers for all-optical control

Photoacoustic microscopy (PAM) combines the advantages of both optical and ultrasound imaging in a hybrid imaging modality. It provides label-free imaging with optical contrast and the increased penetration depths of ultrasound imaging compared to optical imaging. Recently, PAM has seen growing interest in imaging developmental biology as well as clinical applications such as endoscopy. These areas have also seen greater application of microelectromechanical systems (MEMS) scanning mirrors to increase image acquisition speed and reduce the overall size of systems.
We present a novel 3D PAM system with MEMS optical scanning and fibre tip transducer detection to provide an all-optical system for in vitro cellular and sub-cellular resolution imaging. A 1 mm diameter, electrostatically actuated 2-axis MEMS scanner (Mirrorcle MEMS) provides optical scan angles of ±10°, allowing a large field of view without motion induced artefacts caused by stage scanning. An additional focus tunable lens allows the excitation beam to be scanned in the axial direction. The flexibility of being able to rapidly scan the focus of the excitation beam in 3-dimensions allows selective imaging of regions of interest within the samples. The 20 MHz fibre tip transducers allow for a variety of sample chambers to be used including well plates and petri-dishes, providing increased flexibility in terms of sample mounting and preparation.
The flexibility and small size of the system make it possible to integrate with other imaging modalities such as lightsheet microscopy to harness both fluorescence labelled and label-free contrast of 3D samples.