Deep tissue applications (>1 cm) for photoacoustic imaging are limited for traditional Fabry-Perot (FP) ultrasound transducers interrogated by tightly focused Gaussian beams due to beam walk-off, but are in principle feasible for plano-concave optical microresonator (PCMR) sensors. However, in practice, making PCMR sensors with sufficiently high sensitivity is challenging. We explore several approaches to maximise sensitivity and overcome the limitations associated with using high-Q PCMR sensors. The results show an improvement in the sensitivity and the minimum detectable pressure, enabling an increase of the penetration depth in tomographic photoacoustic imaging.
The impact of optical absorption in the spacer layer of Fabry-Pérot (FP) ultrasound sensors is discussed. It is shown that absorption significantly limits the sensitivity of planoconcave microresonators (PCMRs; FP type sensors with a planoconcave geometry). Using materials of lower absorption or selecting sensor interrogation wavelengths to avoid absorption peaks in existing spacer materials could provide at least an order of magnitude higher sensitivity, paving the way to multi-cm deep-tissue PA imaging applications.
Fabry-Pérot (FP) polymer film sensors are used as ultrasound sensors for Photoacoustic (PA) imaging. Optical models predict that FP sensors should have higher sensitivity than observed experimentally. The models assume FP sensors to be optically flat whereas in practice the polymer film spacer exhibits a degree of surface roughness. To understand the impact of the roughness, an optical model of rough FP sensors was developed. Theoretical results show that roughness can reduce the optical sensitivity by a factor of two. The model will help to guide the design of FP sensors to optimize their sensitivity and, therefore, the imaging depth.
Deep tissue applications (>1 cm) for photoacoustic imaging are currently limited for traditional Fabry-Pérot ultrasound transducers interrogated by tightly focused Gaussian beams due to beam walk-off. We investigate the optical confinement of the beam using plano-concave microresonators with a model based on the ABCD formalism and the use of high-sensitive and high-density multi-element arrays. The results show an improvement in the sensitivity enabling an increase of the penetration depth in tomographic photoacoustic imaging.
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