[Paper Review] Single multimode fiber for in vivo light-field encoded nano-imaging

Wen Zhong, Zhenyu Dong+10 more|arXiv (Cornell University)|Jul 7, 2022

Advanced Fluorescence Microscopy Techniques4 citations

TL;DR

This paper presents STABLE nano-endoscopy, a single multimode fiber endoscope enabling in vivo 3D subcellular imaging with sub-diffraction-limited resolution (250 nm) through a 250 µm fiber. By combining spatial-frequency tracking for disorder compensation and full-vector modulation with fluorescence emission difference, it achieves 1000 Hz imaging stability over 200 m, enabling cross-scale light-field nano-imaging in living tissue.

ABSTRACT

Super-resolution microscopy normally requiring complex and cumbersome optics is not applicable for in situ imaging through a narrow channel. Here, we demonstrate single hair-thin multimode fiber (MMF) endoscope (less than 250 $μm$) for in vivo light-field nano-imaging, which is called spatial-frequency tracking adaptive beacon light-field encoded nano-endoscopy (STABLE nano-endoscopy) that enables three-dimensional (3D) subcellular-scale imaging. Spatial-frequency tracking provides up to $10^3$ Hz disorder tracking that ensures stable imaging in long-haul MMFs (up to 200 m) under various conditions. Full-vector modulation and fluorescence emission difference are combined to enhance the imaging signal-to-noise ratio two times and to improve the resolution to sub-diffraction-limited 250 nm ($λ/3NA$). STABLE nano-endoscopy and white-light endoscopy (WLE) are integrated to achieve cross-scale in vivo imaging inside the lumen. This high-resolution and robust observation in a minimally invasive manner paves the way to gain a deeper understanding of the disease mechanisms and to bridge clinical and biological sciences.

Motivation & Objective

• To overcome the limitations of conventional super-resolution microscopy in narrow, in vivo environments.
• To enable high-resolution, three-dimensional in vivo imaging through a single, hair-thin multimode fiber (less than 250 µm).
• To develop a robust imaging system capable of long-haul transmission (up to 200 m) in biologically dynamic environments.
• To integrate light-field encoded nano-imaging with white-light endoscopy for cross-scale in vivo visualization.

Proposed method

• Spatial-frequency tracking is employed to dynamically compensate for mode disorder in multimode fibers, enabling real-time stabilization at up to 1000 Hz.
• Full-vector modulation of the excitation light is used to enhance signal-to-noise ratio and improve resolution beyond the diffraction limit.
• Fluorescence emission difference is combined with light-field encoding to further suppress background noise and enhance contrast.
• A hybrid imaging system integrates STABLE nano-endoscopy with white-light endoscopy (WLE) for simultaneous macro- and nano-scale visualization.
• The system uses a single multimode fiber as both the delivery and collection path, minimizing invasiveness.
• Adaptive beacon feedback is used to track and correct for dynamic environmental perturbations during long-haul imaging.

Experimental results

Research questions

• RQ1 Can a single multimode fiber enable stable, high-resolution 3D in vivo nano-imaging despite strong mode mixing and environmental fluctuations?
• RQ2 How can spatial-frequency tracking achieve real-time, high-bandwidth compensation for mode disorder in long multimode fibers?
• RQ3 To what extent can full-vector modulation and fluorescence emission difference enhance signal-to-noise ratio and resolution in a fiber-based endoscope?
• RQ4 Can STABLE nano-endoscopy be integrated with white-light endoscopy for cross-scale in vivo imaging in living tissues?
• RQ5 What is the achievable resolution and frame rate in a minimally invasive, single-fiber endoscopic platform for in vivo applications?

Key findings

• The system achieves sub-diffraction-limited resolution of 250 nm, corresponding to λ/(3NA), in in vivo 3D imaging through a single 250 µm multimode fiber.
• Spatial-frequency tracking enables real-time disorder compensation at up to 1000 Hz, ensuring stable imaging over 200 m of multimode fiber.
• The combination of full-vector modulation and fluorescence emission difference improves the signal-to-noise ratio by a factor of two.
• The system enables cross-scale imaging by integrating STABLE nano-endoscopy with white-light endoscopy (WLE) for simultaneous macro- and nano-scale visualization.
• In vivo imaging is demonstrated in living tissue with high stability and resolution, validating the platform’s robustness and clinical potential.
• The method is published in Nature Photonics (2023), with a DOI of 10.1038/s41566-023-01240-x.