All-Optical Rotational Ultrasound Imaging

Abstract

Miniaturised high-resolution imaging devices are valuable for guiding minimally invasive procedures such as vascular stent placements. Here, we present all-optical rotational B-mode pulse-echo ultrasound imaging. With this device, ultrasound transmission and reception are performed with light. The all-optical transducer in the probe comprised an optical fibre that delivered pulsed excitation light to an optical head at the distal end with a multi-walled carbon nanotube and polydimethylsiloxane composite coating. This coating was photoacoustically excited to generate a highly directional ultrasound beam perpendicular to the optical fibre axis. A concave Fabry-Pérot cavity at the distal end of an optical fibre, which was interrogated with a tuneable continuous-wave laser, served as an omnidirectional ultrasound receiver. The transmitted ultrasound had a −6 dB bandwidth of 31.3 MHz and a peak-to-peak pressure of 1.87 MPa, as measured at 1.5 mm from the probe. The receiver had a noise equivalent pressure <100 Pa over a 20 MHz bandwidth. With a maximum outer probe diameter of 1.25 mm, the probe provided imaging with an axial resolution better than 50 µm, and a real-time imaging rate of 5 frames per second. To investigate the capabilities of the probe, intraluminal imaging was performed in healthy swine carotid arteries. The results demonstrate that the all-optical probe is viable for clinical rotational ultrasound imaging.

Optically Generated Ultrasound for Intracoronary Imaging

“…In contrast to piezoelectric receivers, whose sensitivities fall off with decreasing element size, fiber optic receivers can maintain their sensitivity even at scales of tens or hundreds of micrometers. Their small lateral dimensions (<250 μm outer diameter) enable integration into intracoronary imaging devices, and their large bandwidths yield high imaging performance [e.g., axial resolution better than 60 μm and cm-scale imaging depths without temporal averaging ( 20 )]. Several other fiber optic reception technologies are promising for intracoronary imaging, including fiber Bragg gratings ( 21 – 23 ) and microring resonators ( 24 , 25 ).…”

“…With OpUS, high bandwidths and pressures have enabled imaging with resolutions better than 50 μm and tissue penetration depths >20 mm ( 20 ). These values challenge those of conventional 40 MHz IVUS technology and show great potential for future clinical application.…”

“…Numerous features of atherosclerotic plaque were identifiable, including a lipid pool, a calcified nodule, and the different layers of the vessel wall. Several other configurations relevant to intracoronary imaging have subsequently been developed, including side-viewing rotational imaging ( 20 ) and hybrid multimodality imaging ( 9 ).…”

“…Image acquisition occurred with a frame rate of 5 frames per second. The imaging fidelity of the device was investigated with ex-vivo swine carotid tissue [( 20 ); Figure 2B ]. The broad bandwidths achieved (−6 dB bandwidth of 31.3 MHz), in conjunction with depth-dependent digital frequency filtering, allowed for both high axial resolutions at shallow depths and deep tissue visualization.…”

Large area all-optical ultrasound imaging using robotic control

“…4 Further, real-time rotational imaging using optical fibres has been demonstrated on ex vivo swine carotid arteries. 6 Additionally, the combination of all-optical robotics has demonstrated the potential for its use to provide feedback and improve robotic control. 7 In this study we combined a robotic manipulator with a fibre optic ultrasound probe, which comprised a nanocomposite coated multimode fibre for ultrasound generation and a concave Fabry-Pérot fibre optic hydrophone for ultrasound reception.…”