New Camera Inspired by Butterfly Eyes

By mimicking the intri­cate visual system of a butterfly, researchers have created a camera that provides surgeons with both a tradi­tional color image as well as a near-infrared image that makes fluores­cently labeled cancerous cells visible even under bright surgical lighting. The new camera is designed to help surgeons remove all the cancerous cells without damaging healthy tissue, making it less likely that the cancer will spread and reducing the need for multiple surgeries.

A new camera mimics the visual system of the morpho butterfly. The butterfly’s eyes contain nanostructures that sense multispectral information, providing an ideal way to acquire both near-infrared and color information simultaneously. (Source: A. Jerez Roman & J. L. Vazquez)

“Instead of putting together commer­cially available optics and sensors to build a camera for image-guided surgery, we looked to nature’s visual systems for inspi­ration,” said research team leader Viktor Gruev from the University of Illinois at Urbana-Champaign. “The morpho butterfly, whose eyes contain nano­structures that sense multi­spectral infor­mation, can acquire both near-infrared and color infor­mation simul­taneously.” The researchers demon­strate that their bioinspired camera can detect tumors in animals and is useful for assessing the stage of breast cancer in people. The new camera offers very sensitive fluores­cence detec­tion even under standard operating room lighting, weighs less than an AA battery, and can be manu­factured for around $20.

“During surgery, it is imperative that all the cancerous tissue is removed, and we’ve created an imaging platform that could help surgeons do this in any hospital around the world because it is small, compact and inex­pensive,” said Gruev. “Although we’ve addressed the instru­mentation side, fluorescent markers targeted for cancer and approved for use in people are needed for our technology to find wide­spread appli­cation. Several of these are in clinical trials now, so we should see progress in this area soon.” The new camera greatly improves upon today’s cameras that are approved by the US Food and Drug Adminis­tration (FDA) for viewing fluores­cent markers during surgery. Many existing near-infrared cameras lack the sensi­tivity to detect fluores­cence markers under surgical settings, so the room lights must be dimmed to view the fluore­scence.

Another problem with today’s infrared imagers is that the fluores­cence image is not always precisely aligned, or coregis­tered, with the tissue it arises from. This happens because FDA-approved instruments use multiple optical elements, such as beam splitters and relay lenses, to separate the visible and infrared wave­lengths, so that each can be sent to separate detectors. Slight tempera­ture changes in the room can affect the optics in these instru­ments causing image misalign­ments that could cause a surgeon to miss cancerous tissue while unneces­sarily removing healthy issue.

“We realized that the problems of today’s infrared imagers could be miti­gated by using nano­structures similar to those in the morpho butter­fly,” said Missael Garcia, a post-doctoral researcher at Univer­sity of Illinois at Urbana-Champaign. “Their compound eyes contain photo­receptors located next to each other such that each photo­receptor senses different wave­lengths of light in a way that is intrin­sically coregis­tered.”

The new camera uses a setup similar to the butterfly eye by inter­lacing various nanoscale structures with an array of photo­detectors, enabling collection of color and near-infrared fluores­cence infor­mation on one imaging device. Inte­grating the detector and imaging optics into a single monolithic sensor keeps the device small, inexpen­sive and insen­sitive to tempera­ture changes.

The design uniquely solves the sensi­tivity problem by allowing each pixel to take in the number of photons needed to build up an image. It doesn’t take long to create the visual-wave­length image for viewing the anatomy since the visible illumination in the lab is high. On the other hand, because fluores­cence is typically dim, it takes longer to collect a suffi­cient number of photons to build up a suffi­ciently bright image. By changing the exposure time to allow each pixel to detect the photons it needs, a bright fluores­cence image can be created without over­exposing the color image of the tissue.

The researchers tested their new instru­ment on a mouse model that develops sponta­neous breast cancer. This means that the exact location where the cancer will grow is unknown as is the number of cancer cells. Using fluores­cent labels that bind to cancer cells, the researchers showed that their bio­inspired imager enabled tumor detection with an accuracy and sensi­tivity sur­passing state-of-the-art infrared cameras FDA-approved for image-guided surgery.

The researchers also tested the ability of their infrared camera to identify lymph nodes in 11 patients with breast cancer at Washington Univer­sity School of Medicine in St. Louis. Because the lymph nodes are one of the primary places where breast cancer spreads, surgeons check them to determine the cancer stage. The patients were injected with FDA-approved indo­cyanine green fluorescent dye that accu­mulates passively in the lymph nodes and then fluores­cence images from the bioinspired imager were displayed either on a screen or projected onto goggles worn by the surgeons.

“We showed that under bright surgical lights, our instrument was a thousand times more sensitive to fluores­cence than the imagers currently approved for infrared image-guided surgery,” said Gruev. “Because the bio­inspired imager can reveal fluores­cence that is deep in the tissue, it sped up the process of lymph node identi­fication and helped surgeons find lymph nodes that couldn’t be seen by eyesight alone.”

According to the researchers, the bio­inspired imager would be useful for removing various types of cancers, including melanomas, prostate cancer and head and neck cancers. Because of its small size it could also be inte­grated into an endoscope to look for cancer during a colo­noscopy, for example. “One big advantage of our instrument is its compact size,” said Garcia. “We tested our instrument in a hospital where space was tight and saw that it didn’t intrude on the surgical workflow.” The researchers are now forming a start-up company to commer­cialize their bio­inspired imager and are also working with the FDA to design a clinical trial in which the surgeons can compare clinical decisions made with the new imager with those that would be made with FDA-approved imagers. (Source: OSA)

Reference: M. Garcia et al.: Bio-inspired imager improves sensitivity in near-infrared fluorescence image-guided surgery, Optica 5, 413 (2018); DOI: 10.1364/optica.5.000413

Link: Dept. of Computer Science and Engineering, Washington University in St. Louis, St. Louis, USA

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