All-Optical Rotational Ultrasound Imaging

Richard J Colchester,Sacha Noimark,Christopher D Loder,Adrien E Desjardins,Erwin J Alles,Paul C Beard,Ioannis Papakonstantinou,Callum Little,Malcolm C Finlay,George Dwyer,Roby D Rakhit,Edward Z Zhang,Ivan P Parkin

doi:10.1038/s41598-019-41970-z

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.

Highlights

High-frequency ultrasound can provide detailed visualisation of tissue for guidance and diagnostics during minimally invasive surgery[1,2], for example it has been shown to improve outcomes during coronary artery stent placement[3]
A highly directional optical ultrasound transmitter was paired with an omnidirectional receiver (Fig. 1(a))
The flat epoxy surface was coated with an ultrasound-generating composite material comprising functionalised multi-walled carbon nanotubes (MWCNT) and medical-grade polydimethylsiloxane (PDMS)[20]

Summary

Introduction

High-frequency ultrasound can provide detailed visualisation of tissue for guidance and diagnostics during minimally invasive surgery[1,2], for example it has been shown to improve outcomes during coronary artery stent placement[3]. Miniature OpUS transducers fabricated on optical fibres[9,10,11,13,15,20] have several promising features, including broad bandwidths, high sensitivity, and immunity to electromagnetic interference. The broad bandwidths and high sensitivity allow for pulse-echo ultrasound imaging with high axial resolution and large imaging depths, respectively; the immunity to electromagnetic interference allows for compatibility with other medical devices such as radiofrequency ablation catheters[21]. Another promising feature of all-optical techniques is the ability to integrate other optical modalities, such as photoacoustic imaging, via the optical fibres used to transmit and receive ultrasound[22]. We present innovations to overcome these challenges, and demonstrate the translational potential of the OpUS imaging probe with imaging of vascular tissue

Methods

Results

Conclusion