Real-time and Freehand Multimodal Imaging: Combining White Light Endoscopy with All-Optical Ultrasound

Minimally invasive surgery offers significant benefits over open surgery in terms of patient recovery, complication rates, and cost. Accurate visualisation is key for successful interventions; however, no single imaging modality offers sufficient resolution, penetration, and soft-tissue contrast to adequately monitor interventional treatment. Consequently, multimodal interventional imaging is intensively investigated. All-optical ultrasound (AOUS) imaging is an emerging modality where light is used to both generate and detect ultrasound. Using fibre-optics, highly miniaturised imaging probes can be fabricated that yield high-quality pulse-echo images and are readily integrated into minimally invasive interventional instruments. In this work, we present the integration of a miniature (diameter: 800 µm), highly directional AOUS imaging probe into a commercially available white light urethroscope, and demonstrate the first real-time, 3D multimodal imaging combining AOUS and white light endoscopy. Through the addition of an electromagnetic tracker, the position and pose of the instrument could be continuously recorded. This facilitated accurate real-time registration of the imaging modalities, as well as freehand operation of the instrument. In addition, the freehand imaging paradigm allowed for “piece-wise” scanning where the instrument was retracted and repositioned without recalibration. The presented imaging probe and system could significantly improve the quality of image guidance during interventional surgery.