The human body is a network of complex, interconnected passageways that traverse the cardiovascular, respiratory, and digestive systems. For physicians, reaching and treating diseased or damaged tissues within these narrow, winding arteries, bronchial tubes, and gastrointestinal chambers can be a daunting task. Many of these pathways are not only small in diameter but can also narrow to microscopic sizes, making it challenging to access them for treatment. Medical devices used to navigate and view these areas need to be flexible, maneuverable, and equipped with a light source. One such device is an endoscope—a long, thin, flexible tube that carries light, and often a camera, at its tip. Endoscopes have long been a vital tool for detecting, viewing, and treating various medical conditions such as blood clots in the heart, airway obstructions, and early-stage colon cancer.

However, current endoscopes are not without their limitations. The size of many endoscopes used today is too bulky to reach smaller spaces within the body, like the arteries in the brain or the bronchioles in the lungs. The size constraint is primarily due to the camera lens and light source needed at the tip of the device, which are essential for detecting, viewing, and treating diseased tissue. In response, researchers have now designed an innovative lens system that could allow physicians to better view and treat areas deep inside the body. The researchers have engineered a metalens—a flat, lightweight optical component that manipulates light through microscopic nanostructures. Metalenses have a wide range of applications in various technologies where space is limited, such as in smartphone cameras.

The tiny, flat metalens designed by the research team at the University of Washington’s Department of Electrical & Computer Engineering (Seattle, WA, USA) could shrink the diameter of the smallest endoscopes by more than 50%. This reduction would allow doctors to access deeper, hard-to-reach areas within the body. The system is incredibly small, with an aperture width of just 0.5 millimeters, about the width of five human hairs side by side. The new metalens system uses quantitative phase imaging, a microscopy technique that measures the phase of light as it passes through a sample, and depth sensing to generate a real-time, full-color, three-dimensional video with minimal computational requirements. While research has explored the use of quantitative phase imaging and depth sensing in other contexts, their application in endoscopic procedures is a unique and innovative development.

Another novel feature of the optical system is the use of chromatic aberration for depth sensing and 3D imaging. Typically, chromatic aberration is seen as an optical flaw that causes colored fringes in images due to a lens's failure to focus all colors at the same point. However, the team found a way to turn this imperfection into an advantage. By using a tiny, flat metalens, they created a chromatic splitting effect, causing each color to converge at different depths. This longitudinal rainbow effect allows depth to be mapped into the color channels of a camera. The results of this study, published in Nature Light: Science & Applications, show that an endoscope with such a lens system could provide real-time visual feedback to physicians, improving the efficiency, accuracy, and success rate of medical procedures. The system also offers higher resolution and better contrast than X-rays without the harmful radiation exposure.

This breakthrough opens up the possibility for physicians to access previously unviewable areas, such as deep blood clots in the brain or diseased arteries throughout the body, including in the heart. This is a promising development, particularly for treating cardiovascular diseases like heart attacks and strokes, which are the leading causes of premature death worldwide. Having developed a proof of concept, the research team now plans to build a prototype to test in a physical model of a human organ. The meta optics technology they have created can be manufactured and scaled up, presenting a unique opportunity to bring this lens system to the medical market. They also aim to guide the technology through clinical trials over the coming decade and beyond.

“We are trying to extend the eyes of the surgeon or the physician deeper into the body,” said Eric Seibel, a UW research professor in mechanical engineering, who co-authored the paper and has been engineering endoscopes for decades. “This is an application of meta optics that has the potential to make a practical impact in everybody’s lives, with a significant amount of development work. It may take 20 more years to make that impact. But it’s a technology that has great potential, and everyone should start paying attention to it.” 

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