Compact and portable scanning fiber-optic confocal microendoscopy system for reflectance and fluorescence imaging

Ongoing research is actively exploring microendoscopy systems for high-resolution imaging and disease diagnosis. State-of-the-art commercial endoscopes use fiber bundles for relaying the image formed by the lens system in the imaging probe head. However, they are expensive and resolution is limited by the spacing between the cores and cross-talk between the pixels. Fiber scanning-based imaging systems are promising due to their ability to be designed with a single fiber alongside micro-objective lenses. However, these systems face a significant challenge when it comes to the necessity of free space optics and photomultiplier tubes for fluorescence detection, which can be tricky in terms of alignment. Furthermore, the existing imaging systems at near-infrared wavelengths utilize double-clad fiber with larger clad for fluorescence collection. We present a compact, low-cost, and portable system for imaging at visible wavelength that utilizes a double-clad fiber of smaller inner clad (diameter of 15 µm) in conjunction with a bandpass filter and Avalanche Photodetector to detect fluorescence emission. To assess the effectiveness of this system, we conducted a study on the performance of an imaging head consisting of a gradient refractive index (GRIN) lens (diameter of 1 mm) as a micro-objective in a fiber-scanning setup by actuating a piezoelectric tube with a fiber channel inside. We demonstrated the reflectance imaging of a standard resolution chart and fluorescence detection from microspheres at 644 nm.