New All-Optical System Could Revolutionize Image-Guided Interventions

For the first time, researchers have demonstrated the use of an all-optical ultrasound imager for video-rate, real-time 2D imaging of biological tissue, marking a significant step towards making all-optical ultrasound practical for routine clinical use. Since all-optical ultrasound systems do not require any electronic components in the imaging probe, they could be safely used at the same time as magnetic resonance imaging (MRI) scanners. This can provide doctors with a more comprehensive picture of the tissues around an area of interest, such as a tumor or blood vessel, according to a recent paper published in the Optical Society (OSA) journal Biomedical Optics Express.

Conventional ultrasound imagers use arrays of electronic transducers to transmit high-frequency sound waves into tissue and receive the reflections, whereas all-optical ultrasound imagers use light to both transmit and receive ultrasound waves. Pulsed laser light is used to generate ultrasound waves, and scanning mirrors control where the waves are transmitted into the tissue. A fiber optic sensor then receives the reflected waves.

The researchers demonstrated how the light source can be manipulated to generate either low frequency ultrasound, resulting in greater penetration into the tissue, or high frequency ultrasound, which offers higher resolution images at a shallower depth. The team tested their prototype system by imaging a deceased zebrafish and a pig artery that was manipulated to emulate the dynamics of pulsing blood. The demonstration showed imaging capabilities comparable to an electronic high-frequency ultrasound system, with a sustained frame rate of 15 Hertz, a dynamic range of 30 decibels, a penetration depth of 6 millimeters and a resolution of 75 by 100 micrometers.

The researchers are now working to adapt the technology for clinical use by developing a long, flexible imaging probe for free-hand operation, as well as miniaturized versions for endoscopic applications. In conventional ultrasound devices, the electronic components make it difficult to miniaturize the devices for internal use. On the other hand, optical components are easily miniaturized and tiny all-optical ultrasound probes are likely be significantly less expensive to manufacture as compared to compact electronic ultrasound systems, according to the researchers.

“All-optical ultrasound imaging probes have the potential to revolutionize image-guided interventions,” said Erwin J. Alles, University College London. “A lack of electronics and the resulting MRI compatibility will allow for true multimodality image guidance, with probes that are potentially just a fraction of the cost of conventional electronic counterparts.”