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Many percutaneous needle-based procedures such as foetal interventions, tumor biopsies, nerve blocks, and central venous catheterizations are guided by ultrasound (US) imaging to identify the procedural target and to visualize the needle. A key challenge associated with ultrasound-guided needle insertions is accurate and efficient identification of the needle tip, as thin needles can readily stray from the imaging plane and can have poor visibility at large insertion angles. Ultrasonic tracking is a method for localising the needle tip relative to the imaging plane in real-time, using an ultrasonic transmitter or receiver integrated into the needle that is in communication with an external ultrasound imaging probe. This study had two foci. The first was to increase the sensitivity with which ultrasound reception was performed, using a custom fiber optic hydrophone with a high-finesse Fabry-Pérot cavity based ultrasound sensor. This sensor, which comprised of a polymer layer sandwiched between dielectric mirrors, was interrogated continuously during insertions into tissue. The second focus of the study was to develop a custom needle stylet into which the fiber optic hydrophone was integrated, which was fully compatible with clinical practice and which could be adapted to different needles. We tested the sensitivity of the sensorized stylet across a wide range of needle angulations, depths and insertion angles in different biological tissues. We demonstrated, for the first time, needle tip localization in ex-vivo tissues at depths beyond 6 cm and insertion angles steeper than 80°. We conclude that ultrasonic tracking with high-finesse Fabry-Pérot fiber optic hydrophone is very promising for use in clinical practice.
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