3D Optical Biopsies within Reach

This is modal structure in optical fiber bundles captures light field information. (Source: M. Capelli, RMIT U.)

Researchers have shown that existing optical fiber tech­nology could be used to produce micro­scopic 3D images of tissue inside the body, paving the way towards 3D optical biopsies. Unlike normal biopsies where tissue is harvested and sent off to a lab for analysis, optical biopsies enable clini­cians to examine living tissue within the body in real-time. This minimally-invasive approach uses ultra-thin micro­endoscopes to peer inside the body for diagnosis or during surgery, but normally produces only two-dimen­sional images.

Research led by RMIT Uni­versity in Melbourne, Australia, has now revealed the 3D potential of the existing micro­endoscope tech­nology. The development is a crucial first step towards 3D optical biopsies, to improve diagnosis and precision surgery. Antony Orth said the new technique uses a light field imaging approach to produce micro­scopic images in stereo vision, similar to the 3D movies that you watch wearing 3D glasses.

“Stereo vision is the natural format for human vision, where we look at an object from two different viewpoints and process these in our brains to perceive depth,” said Orth, a Research Fellow in the RMIT node of the ARC Centre of Excellence for Nano­scale Bio­Photonics (CNBP). “We’ve shown it’s possible to do something similar with the thousands of tiny optical fibers in a micro­endoscope. It turns out these optical fibers naturally capture images from multiple perspec­tives, giving us depth perception at the microscale. Our approach can process all those micro­scopic images and combine the viewpoints to deliver a depth-rendered visuali­zation of the tissue being examined – an image in three dimensions.”

The research revealed that optical fiber bundles transmit 3D infor­mation in the form of a light field. The challenge for the researchers was then to harness the recorded infor­mation, unscramble it and produce an image that makes sense. Their new technique not only overcomes those challenges, it works even when the optical fibre bends and flexes – essential for clinical use in the human body. The approach draws on principles of light field imaging, where tradi­tionally, multiple cameras look at the same scene from slightly different perspec­tives.

Light field imaging systems measure the angle of the rays hitting each camera, recording information about the angular distri­bution of light to create a multi-viewpoint image. But how do you record this angular infor­mation through an optical fibre? “The key obser­vation we made is that the angular distri­bution of light is subtly hidden in the details of how these optical fiber bundles transmit light,” Orth said. “The fibers essen­tially remember how light was initially sent in – the pattern of light at the other side depends on the angle at which light entered the fiber.”

With this in mind, RMIT researchers and colleagues developed a mathe­matical framework to relate the output patterns to the light ray angle. “By measuring the angle of the rays coming into the system, we can figure out the 3D structure of a micro­scopic fluorescent sample using just the information in a single image,” Brant Gibson, Chief Inves­tigator and Deputy Director of the CNBP, said. “So that optical fiber bundle acts like a minia­turised version of a light field camera. The exciting thing is that our approach is fully compatible with the optical fiber bundles that are already in clinical use, so it’s possible that 3D optical biopsies could be a reality sooner rather than later.” In addition to medical appli­cations, the ultra-slim light field imaging device could potentially be used for in vivo 3D fluores­cence micro­­scopy in biological research. (Source: RMIT U.)

Reference: A. Orth et al.: Optical fiber bundles: Ultra-slim light field imaging probes, Sci. Adv. 5, eaav1555 (2019); DOI: 10.1126/sciadv.aav1555

Link: ARC Centre of Excellence for Nanoscale BioPhotonics, School of Science, RMIT University, Melbourne, Australia

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