Zhang, Shaoyan; Bodian, Semyon; Zhang, Edward; Beard, paul; Noimark, Sacha; Desjardins, Adrien; Colchester, Richard; (2022) Miniaturised dual-modality all-optical Laser Interstitial Thermal Therapy (LITT) and ultrasound imaging. Presented at: IEEE International Ultrasonics Symposium, Venice, Italy.

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Abstract

Introduction: Laser Interstitial Thermal Therapy (LITT) is a minimally invasive procedure to treat kidney tumours that can be hard to reach with open surgery, with low risks and fast recovery time. This treatment requires robust real-time imaging modalities to track tumour treatment outcomes and avoid damage of healthy tissue during the procedure. All-optical ultrasound (OpUS) is an emerging imaging paradigm that exhibits high imaging resolution, ease of miniaturisation and immunity to electromagnetic interference [1]. With OpUS, the ultrasound wave is generated via photoacoustic effect, with pulsed excitation light delivered to an optically absorbing coating on the end of an optical fibre and received using a plano-concave microresonator on an optical fibre end face. The use of optical fibres allows laser ablation and OpUS imaging to be integrated into a miniaturised device, suitable for the real-time monitoring of tissue damage during LITT procedures. In this work, we developed an optical-fibre-based miniaturised device that combines LITT and OpUS imaging. To assess the capability, the device was used to perform LITT with in situ OpUS lesion imaging on an ex vivo lamb kidney. / Methods: The OpUS device comprised three optical fibres; a multimode optical fibre (200 µm core) coated with Candle soot nanoparticles (CSNPs)-polydimethylsiloxane (PDMS) composite for ultrasound transmission, an single mode optical fibre with a plano-concave microresonator for ultrasound reception and a multimode optical fibre (400 µm core) for delivery of laser ablation light. The distal end face of the ultrasound transmitter and receiver were aligned at their distal tips, whilst the ablation fibre was advanced 10 mm, allowing for the insertion into kidney tissue. Prior to carrying out LITT, a B-mode OpUS image of the kidney tissue was acquired. For LITT experiments, the ablation fibre was inserted into the ex vivo kidney tissue and laser treatment was applied (808 nm, 3.0 W, 60 s) whilst performing concurrent M-mode imaging with the OpUS probe to track the lesion formation. / Results & Discussion: B-mode OpUS imaging provided an imaging depth > 15 mm and high imaging resolution that delineated the structure boundaries inside the kidney (Fig 1. a). M-mode OpUS imaging allowed visualisation of the tissue throughout the procedure. When the ablation laser was switched on the tissue contrast changed immediately, indicating the formation of an ablated lesion (Fig 1. b). Throughout the ablation period, the lesion grew bidirectional from the optical fibre tip in the vertical dimension, which was visible on the M-mode image as increasing brightness and changing contrast. This work demonstrated the feasibility of OpUS imaging to monitor the lesion growth during LITT.

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