Intravascular ultrasound (IVUS) imaging probes can be invaluable for guiding minimally invasive procedures such as coronary stent placement. With current IVUS catheters, ultrasound is generated and received electrically. With electronic transducer elements, it is challenging to achieve wide bandwidths, high sensitivity, and small dimensions suitable for intracoronary imaging. Here we present an all-optical ultrasound (OpUS) transducer, which uses light within fibre-optics to generate and receive ultrasound. These devices have several distinguishing advantages, including the potential to generate and receive wideband ultrasound (tens of MHz) required for high resolution imaging. The side-viewing OpUS transducer is highly miniaturised (< 1.5 mm diameter) with two optical fibres for transmission and reception, and a rotational mechanism for circumferential imaging. The transmitter is a composite of carbon nanotubes and PDMS coated on a multimode fibre tip. Ultrasound is generated within this coating by the photoacoustic effect. The receiver comprises a concave Fabry-Pérot cavity on a single mode fibre tip. Images acquired with the OpUS transducer were characterised using wire phantoms and post-mortem vascular tissue with stents. The axial resolution of this device was less than 70 microns, and the sensitivity was found to be sufficient to resolve pathological features. Subsequently, imaging was conducted in a healthy swine model in vivo and pulsatile motions of the artery were visualised with high fidelity. These studies show the strong potential for all-optical ultrasound to guide minimally invasive surgery.
Richard J. Colchester, Sacha Noimark, Edward Z. Zhang, Malcolm C. Finlay, Callum Little, Chris D. Loder, Roby D. Rahkit, Ivan P. Parkin, Paul C. Beard, Ioannis Papakonstantinou, and Adrien E. Desjardins, "All-optical side-viewing intravascular ultrasound imaging probe (Conference Presentation)," Proc. SPIE 10471, Diagnostic and Therapeutic Applications of Light in Cardiology 2018, 104710V (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289848.5751469715001.
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