Ultrahigh-resolution and high contrast photoacoustic imaging using STED-inspired array beamformation.

In this study, we proposed what is believed to be a novel photoacoustic (PA) array beamforming technique, inspired by stimulated-emission-depletion fluorescence microscopy (STED)-hyper-beamforming (HBF)-enabling ultrahigh-resolution, high-contrast PA array imaging while maintaining comparable computational complexity to delay-and-sum beamforming (DAS), i.e., back-projection, the most common algorithm. HBF calculates two beam patterns, which resemble the excitation and depletion beams in STED, respectively, and generates a hyper-beam with a narrow mainlobe and low sidelobes by exploiting the difference between the two; thereby providing better lateral resolution and imaging contrast. Moreover, an adjustable power factor n is introduced to emulate the nonlinear effect in STED, thereby tuning HBF's performance. Our phantom and in vivo experimental results show that HBF can achieve ultrahigh-resolution and high-contrast PA array imaging, with an 83.3% narrower mainlobe and a 25 dB lower sidelobe level compared with DAS.