Noise-equivalent Pressures of Ultrasound Detectors Used in Photoacoustic Tomography

Detection sensitivity fundamentally limits imaging depth and signal-to-noise ratio in photoacoustic tomography (PAT). This Primer summarizes the noise-equivalent pressures (NEP) reported in the literature for piezoceramic, piezopolymer, capacitive micromachined ultrasonic transducer (CMUT) and optical ultrasound detectors applicable to PAT as a function of detector size and bandwidth. Millimetre-scale piezoceramic transducers achieve NEPs as low as 0.06 mPa/√Hz, enabling the detection of sub-pascal acoustic pressures at low-megahertz frequencies. Meanwhile, sub-100-µm-sized optical ultrasound sensors can provide NEPs of 0.6 mPa/√Hz, enabling the detection of a few pascals at frequencies in the tens of megahertz range. Piezopolymer detectors, meanwhile, exhibit higher NEPs but with broader bandwidths, whereas CMUTs provide NEPs comparable to the lowest available for 0.1–1-mm-sized detectors, albeit with resonant responses. By establishing and explaining the NEP landscape, this Primer aims to aid the understanding and selection of detectors for PAT and inform their future development. Photoacoustic tomography (PAT) is a biomedical imaging technique based on the use of optically excited ultrasound waves. In this Primer, Guggenheim et al. describe the noise-equivalent pressures reported in the literature for detectors applicable to PAT.