Optics for micro-endoscopy

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Name of the Speaker: Susan Thomas (EE20D751)
Name of the Guide: Dr. Shanti Bhattacharya
Venue: ESB-244 (Seminar Hall)
Date/Time: 28th November 2022, 11.00 am

Early detection and diagnosis of certain diseases like cancer is limited by the ability to obtain high resolution images in deeper body cavities and hollow organs. The present imaging techniques for cancer screening such as ultrasound, MRI and CT have limited ability to detect pre-cancerous lesions. Techniques such as PET are expensive and has issues of low availability. Therefore, it is imperative to develop micro-endoscopes with minimal invasiveness to image cavities inaccessible to standard endoscopes using relatively inexpensive but robust optical components. Free space optical systems can yield the necessary resolution to retrieve structural information for early detection. But they cannot be integrated inside a minimally invasive endoscope penetrating through the body to sufficient depth. Therefore, fiber optics needs to be integrated with miniaturized optical system for endoscopy.

Fluorescence imaging endoscopy is widely explored by researchers to visualize the molecular changes of the tissue. Single photon fluorescence imaging currently employed in the commercial endoscopes for high resolution imaging is limited by tissue penetration depth and phototoxicity. Research trends suggest the scope of two photon fluorescence technique for deeper tissue imaging with high resolution. The conventional two photon imaging is limited to a free space laboratory setup and non-medical applications. The scope of double clad fiber coupler for fiber optic fluorescence imaging is being explored in our study.

In this seminar, we discuss the optical design of an endoscope for two photon fluorescence imaging. The design focus on the getting a homogenous resolution in the full field of view by correcting the optical aberrations and thereby improving the image quality. We also discuss the characterization and demonstration of imaging quality with gradient refractive index lenses as the objective lens for endoscopy. As two photon fluorescence imaging involves two wavelengths, the correction of chromatic aberration is a subject of investigation. We present the incorporation of a phase correction element to address the issue of chromatic focal shift.