Non-contact photoacoustic imaging empowered with a PMUT sensor and refraction correction

This article reports the development of non-contact photoacoustic imaging (nC-PAI)-unlike the conventional PAI that mandates acoustic coupling gel-employing and integrating for the first time: (i) MEMS piezoelectric-micromachined-ultrasound-transducer (PMUT) sensor, (ii) Snell's law-based refraction correction beamforming (S-rC-BForm), and (iii) signal averaging (sA). Quantitative pre-clinical validation studies-both numerical simulations and experiments-were conducted in diversified samples (agar phantoms and chicken breasts). The results demonstrate that our proposed nC-PAI enables achieving spatial-resolution ∼0.6mm, SNR ∼40dB, and contrast-ratio (CR) ∼45dB at depth∼2.5mm (in tissues). Conclusively, the study demonstrates the promising practical applications of our fully contact- or coupling-free nC-PAI in clinical settings where one can not use the acoustic coupling gel, e.g., ophthalmic, skin-burns, intra-operative, wound-healing, and brain-imaging (non-intact skulls).