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.
“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.”
In Optica, The Optical Society's journal for high impact research, 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.
The researchers tested the ability of their infrared camera to identify lymph nodes in patients with breast cancer. Lymph nodes are one of the primary places where breast cancer spreads. The camera detects indocyanine green fluorescent dye, which accumulates passively in the lymph nodes. Image Credit: Missael Garcia, Julie Margenthaler and Viktor Gruev
“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 U.S. 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 realised 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 and lead author of the paper.
“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.
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Image credit: OSA.