Nano-Endoscope with Metalenses

Scanning electron micrograph image of a portion of a fabricated metalens used in nano-optic endoscopes. (Source: Harvard U. / MGH)

The diagnosis of diseases based in internal organs often relies on biopsy samples collected from affected regions. But collecting such samples is highly error-prone due to the inability of current endo­scopic imaging techniques to accu­rately visualize sites of disease. The conven­tional optical elements in catheters used to access hard-to-reach areas of the body, such as the gastro­intestinal tract and pulmonary airways, are prone to aber­rations that obstruct the full capa­bilities of optical imaging. Now, experts in endoscopic imaging at Massa­chusetts General Hospital (MGH) and pioneers of flat metalens tech­nology at the Harvard John A. Paulson School of Engi­neering and Applied Sciences (SEAS), have teamed up to develop a new class of endo­scopic imaging catheters – nano-optic endoscopes – that overcome the limi­tations of current systems.

“Clinical adoption of many cutting-edge endo­scopic micro­scopy moda­lities has been hampered due to the diffi­culty of designing miniature catheters that achieve the same image quality as bulky desktop micro­scopes,” said Melissa Suter, an assistant professor of Medicine at MGH and Harvard Medical School (HMS). “The use of nano-optic catheters that incor­porate meta­lenses into their design will likely change the landscape of optical catheter design, resulting in a dramatic increase in the quality, reso­lution, and func­tionality of endo­scopic micro­scopy. This will ulti­mately increase clinical utility by enabling more sophis­ticated assess­ment of cell and tissue micro­structure in living patients.”

“Meta­lenses based on flat optics are a game changing new tech­nology because the control of image distor­tions necessary for high resolution imaging is straight­forward compared to conven­tional optics, which requires multiple complex shaped lenses,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engi­neering at SEAS. “I am confident that this will lead to a new class of optical systems and instru­ments with a broad range of appli­cations in many areas of science and tech­nology.”

“The versa­tility and design flexibility of the nano-optic endoscope signi­ficantly elevates endoscopic imaging capa­bilities and will likely impact diagnostic imaging of internal organs,” said Hamid Pahlevani­nezhad, Instructor in Medicine at MGH and HMS. “We demons­trated an example of such capa­bilities to achieve high-reso­lution imaging at greatly extended depth of focus.” To demons­trate the imaging quality of the nano-optic endoscope, the researchers imaged fruit flesh, swine and sheep airways, and human lung tissue. The team showed that the nano-optic endoscope can image deep into the tissue with signi­ficantly higher resolution than provided by current imaging catheter designs.

The images captured by the nano-optic endo­scope clearly show cellular structures in fruit flesh and tissue layers and fine glands in the bronchial mucosa of swine and sheep. In the human lung tissue, the researchers were able to clearly identify structures that correspond to fine, irregular glands indicating the presence of adeno­carcinoma, the most prominent type of lung cancer.

“Currently, we are at the mercy of materials that we have no control over to design high resolution lenses for imaging,” said Yao-Wei Huang, a post­doctoral fellow at SEAS. “The main advantage of the metalens is that we can design and tailor its speci­fications to overcome spherical aber­rations and astig­matism and achieve very fine focus of the light. As a result, we achieve very high reso­lution with extended depth of field without the need for complex optical components.” Next, researchers aim to explore other appli­cations for the nano-optic endo­scope, including a polari­zation-sensi­tive nano-optic endoscope, which could contrast between tissues that have highly-organized structures, such as smooth muscle, collagen and blood vessels. (Source: SEAS)

Reference: H. Pahlevaninezhad et al.: Nano-optic endoscope for high-resolution optical coherence tomography in vivo, Nat. Phot., online 30 July 2018; DOI: 10.1038/s41566-018-0224-2

Link: Capasso Group, Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, USA

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