An all-fiber-optic endoscopy platform for simultaneous OCT and fluorescence imaging

Abstract

We present an all-fiber-optically based endoscope platform for simultaneous optical coherence tomography (OCT) and fluorescence imaging. This design entails the use of double-clad fiber (DCF) in the endoscope for delivery of OCT source and fluorescence excitation light while collecting the backscattered OCT signal through the single-mode core and fluorescence emission through the large inner cladding of the DCF. Circumferential beam scanning was performed by rotating a 45° reflector using a miniature DC motor at the distal end of the endoscope. Additionally, a custom DCF coupler and a wavelength division multiplexer (WDM) were utilized to seamlessly integrate both imaging modalities to achieve an entirely fiber-optically based dual-modality imaging system. We demonstrated simultaneous intraluminal 3D OCT and 2D (surface) fluorescence imaging in ex vivo rabbit esophagus using the dual-modal endomicroscopy system. Structural morphologies (provided by OCT) and fluorophore distribution (provided by the fluorescence module) could be clearly visualized, suggesting the potential of the dual-modality system for future in vivo and clinical applications.

Keywords: (170.2150) Endoscopic imaging; (170.4500) Optical coherence tomography; (170.6280) Spectroscopy, fluorescence and luminescence.

Fig. 1

Schematic of the dual-modality system capable of performing endoscopic OCT and fluorescence imaging simultaneously. FDML: Fourier-domain mode-locking fiber laser; OC: Optical coupler (OC1 95/5, OC2 70/30, OC3 50/50); MZI: Mach-Zehnder interferometer; CIR: Circulator; PC: Polarization controller; BD: Balanced detector; WDM: Wavelength division multiplexer; DCFC: double-clad fiber coupler; PMT: Photomultiplier tube; F: Bandpass filter; Green: Multimode fiber (MMF); Blue/Red: Double-clad fiber (DCF); Black: Single-mode fiber (SMF-28e).

Fig. 2

(A) Schematic of distal end of the dual-modal endoscope design. (B) Photograph of a precision-cut metal enclosure (of an outer diameter 2.4 mm) with minimal beam blockage (i.e., less than 5%). (C) A photograph of the constructed endoscope of an overall diameter of 2.9 mm including the housing transparent sheath.

Fig. 3

Circumferential scanning and pull back were performed to obtain 3D volumetric OCT images and 2D fluorescence surface map of the esophagus with the endoscope. (A) Representative 2D cross-sectional OCT image of ex vivo rabbit esophagus during one circumferential scan (grayscale) with the overlaid inner annulus (red hot color map) of the fluorescence intensity. (B) The cut-away view of the 3D OCT volumetric image (grayscale) and the 2D fluorescence intensity map inlaid (red hot color map) on top of the OCT image. In both the 2D OCT cross-sectional image and 3D volumetric OCT image the normal layered structures of the esophagus can be clearly visualized, including the epithelium (E), lamina propria (LP), muscularis mucosa (MM), and glands (G). The co-registered and simultaneously acquired fluorescence map shows striated structures which are believed to be vasculature [24] (see Media 1).

Fig. 4

(A) Unwrapped 2D Fluorescence image. (B-D) Unwrapped OCT images at 700 µm, 1400 µm, and 2100 µm depth. The white arrows on the OCT images (B-D) correspond to the black arrows in the fluorescence map (A) indicating correlating structures such as vasculature (V), suture (S), and metal strut (MS). The suture was used to provide a registration mark for both OCT and fluorescence intensity images.