Photoacoustic Imaging With Single-Element, Low-Frequency Thin-Film PMUT

Abstract

For the first time, we present photoacoustic (PA) imaging using a single-element (single-cell) piezoelectric micromachined ultrasound transducer (PMUT) with a low resonant frequency of approximately 1 MHz and a compact effective aperture as tiny as 0.06 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> . Adding to this innovation, we introduce pioneering image enhancement techniques applied directly to images obtained from this standalone single-cell PMUT, aiming to elevate and refine PA image quality. Our approach employs a trio of advanced methods: 1) frame averaging to ensure clarity by reducing image clutter; 2) cutting-edge mathematical algorithms to fine-tune image quality metrics; and 3) precise hardware positioning for accurate image capture. These techniques underwent rigorous validation using both agar phantom and ex-vivo tissue samples. As benchmarks for our progress, we utilized quantifiers including full width at half maximum (FWHM), signal-to-noise ratio (SNR), and contrast ratio (CR). Our results were striking: a 34% improvement in FWHM, a 23% boost in SNR, and a 25% enhancement in CR. These numbers clearly demonstrate the efficacy of our methods in optimizing PA images through a low-frequency PMUT-based detector. In conclusion, our research indicates that these enhancement methods could be instrumental in shaping a cost-effective and efficient future for PMUT-based photoacoustic imaging (PAI) systems.