High-speed, ultrahigh-resolution distal scanning OCT endoscopy at 800 nm for in vivo imaging of colon tumorigenesis on murine models.

ABSTRACT

We present the first, most compact, ultrahigh-resolution, high-speed, distal scanning optical coherence tomography (OCT) endoscope operating at 800 nm. Achieving high speed imaging while maintaining an ultrahigh axial resolution is one of the most significant challenges with endoscopic OCT at 800 nm. Maintaining an ultrahigh axial resolution requires preservation of the broad spectral bandwidth of the light source throughout the OCT system. To overcome this critical limitation we implemented a distal scanning endoscope with diffractive optics to minimize loss in spectral throughput. In this paper, we employed a customized miniature 900 µm diameter DC micromotor fitted with a micro reflector to scan the imaging beam. We integrated a customized diffractive microlens into the imaging optics to reduce chromatic focal shift over the broad spectral bandwidth of the TiSapphire laser of an approximately 150 nm 3dB bandwidth, affording a measured axial resolution of 2.4 µm (in air). The imaging capability of this high-speed, ultrahigh-resolution distal scanning endoscope was validated by performing 3D volumetric imaging of mouse colon in vivo at 50 frames-per-second (limited only by the A-scan rate of linear CCD array in the spectral-domain OCT system and sampling requirements). The results demonstrated that fine microstructures of colon could be clearly visualized, including the boundary between the absorptive cell layer and colonic mucosa as well the crypt patterns. Furthermore, this endoscope was employed to visualize morphological changes in an enterotoxigenic Bacteriodes fragilis (ETBF) induced colon tumor model. We present the results of our feasibility studies and suggest the potential of this system for visualizing time dependent morphological changes associated with tumorigenesis on murine models in vivo.