Removal of back-reflection noise at ultrathin imaging probes by the single-core illumination and wide-field detection

Youngwoon Choi,Changhyeong Yoon,Jin H. Hong,Jingchao Xing,Hongki Yoo,Munkyu Kang,Taeseok D. Yang,Wonshik Choi

doi:10.1038/s41598-017-07024-y

Youngwoon Choi, Changhyeong Yoon + Show 6 more

Open Access

https://doi.org/10.1038/s41598-017-07024-y

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Abstract

Thin waveguides such as graded-index lenses and fiber bundles are often used as imaging probes for high-resolution endomicroscopes. However, strong back-reflection from the end surfaces of the probes makes it difficult for them to resolve weak contrast objects, especially in the reflectance-mode imaging. Here we propose a method to spatially isolate illumination pathways from detection channels, and demonstrate wide-field reflectance imaging free from back-reflection noise. In the image fiber bundle, we send illumination light through individual core fibers and detect signals from target objects through the other fibers. The transmission matrix of the fiber bundle is measured and used to reconstruct a pixelation-free image. We demonstrated that the proposed imaging method improved 3.2 times on the signal to noise ratio produced by the conventional illumination-detection scheme.

Highlights

Endoscopy enables us to visualize objects whose line of sight is blocked by intervening layers
The illumination was delivered through single core fibers in the image fiber bundle, but the signal waves were detected by the other core fibers
Since this unique imaging scheme requires a target object to be placed at a distance from the surface of the fiber bundle, the signals detected at the other core fibers cannot form an object image

Summary

Introduction

Endoscopy enables us to visualize objects whose line of sight is blocked by intervening layers. Despite being simple in structure, these probes support the high numerical aperture (NA) necessary for microscopic imaging When using such ultrathin imaging probes, the same probe is used for both illumination and collection to limit the dimensions of the endoscope unit to the diameter of the probes. Light reflected from the surface of the probe facing the target object is inevitably detected at the image sensor. The reflectance-mode of imaging, which is directly applicable to in vivo studies in biomedical applications, is extremely susceptible to back-reflection noise Since in this case the wavelengths of illumination and detection are the same, back-reflection noise from imaging probes is indistinguishable from signal light. Way to avoid back-reflection noise is to deliver illumination light through a separate beam path This requires a long working distance, thereby reducing the achievable NA. We demonstrated the imaging of rat intestines exposed to air where strong back-reflection noise is usually introduced

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