Real-Time, Video-Rate and Depth-Resolved Imaging of Radio-Frequency Ablation Using All-Optical Ultrasound

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 c linical 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.