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We propose and demonstrate a miniature microwave device capable of detecting wide-band ultrasound without the use of piezo materials. By the nature of the transduction mechanism, the scheme naturally implements orthogonal frequency division multiplexing (OFDM): each device can be assigned its own microwave band, mitigating electrical cross-talk between adjacent sensor elements for future imaging array systems. Furthermore, the entire array could be addressed with a single electrical connection, since addressing is in the frequency, rather than spatial, domain. We anticipate that the convenience afforded by this fully electronic platform will enable its use as a low cost and versatile solution in cases where high sensitivity is required over a large portion of the acoustic spectrum.

In this work, we demonstrate how the wide acoustic bandwidths generated by all-optical ultrasound imaging probes can be leveraged to dynamically trade-off image resolution with penetration depth. This dynamic trade-off was achieved through temporal modulation of the excitation light using bandwidth-limited linear chirps. The penetration depth of the all-optical ultrasound imaging probe used here could be arbitrarily set between 2 and 15 mm, to achieve inversely proportional spatial resolutions ranging from 128 − 500 μm (lateral)and 189 − 295 μn (axial). This added versatility in image parameters will enable seamless multi-scale ultrasound imaging that can strongly benefit interventional imaging.

Radio-frequency (RF)ablation is an effective minimally invasive treatment for atrial fibrillation, where RF fields are delivered by a catheter within the heart. In current clinical practice, this procedure is performed without real-time feedback about the viability of tissue beneath the ablation lesion. As a result, it can be challenging to perform complete ablation of the target tissue whilst avoiding damage to adjacent structures. Recently, all-optical ultrasound imaging, where ultrasound is both generated and detected using light, has been demonstrated as a viable imaging modality exhibiting high image resolution, strong miniaturisation potential, and resilience to interfererence by electromagnetic (EM)fields from the RF ablation catheter. In this work, the suitability of all-optical ultrasound to monitoring RF ablation lesion delivery is investigated using a bench-top imaging system. This system is capable of real-time, video-rate 2D imaging at an image depth of 15 mm, a resolution of 100 μm, a dynamic range of 35 dB, and a sustained frame rate of 9 Hz. In this paper we present the first real-time, video-rate all-optical ultrasound images acquired during RF ablation, and demonstrate how the imaging system was able to clearly visualise the lesion growth at a contrast of up to 30 dB. In addition, we demonstrated how lesion growth in inhomogeneous tissue can progress in an erratic fashion. High-quality imaging during treatment will enable optimisation of the ablation parameters during treatment, and will minimise both treatment times and complication rates.