Development of a side-view endoscopic imaging probe for combined two photon microscopy (TPM) and optical coherence tomography (OCT)

Abstract

Colorectal cancer has been a major health problem for human beings over the recent years, and current detection method based on optical endoscope is not good enough mainly due to high adenoma missing rate of approximately 22%. Recent developments of detection methods include high-resolution cellular imaging and optical coherence tomography (OCT), where the former is used to diagnose stages of polyps by cellular examination and the latter to detect flat and depressed lesions. Colon study based on animal models is useful to test detection and treatment methods. In this thesis, a side-view endoscopic probe for combined imaging of two-photon microscopy (TPM) and OCT was developed. The imaging system was realized by adding a grin lens based probe in front of an objective lens, which is a typical part of an imaging system. The probe was 2mm in diameter and 60.79mm in length, with a 90° prism attached at the end reflecting the incoming beam by 90°. TPM used a Ti:Sapphire laser and scanned the sample through scanning mirrors, whereas OCT used a wavelength swept source and scanned through the motion of the sample stage along the probe axis. With the objective lens and the probe in common, TPM and OCT worked sequentially and they switched easily by means of a magnetic mirror. The system was characterized by imaging fluorescent microspheres: for TPM module, approximately 1.5 to 2μm lateral resolution, 15.4 frames per second imaging speed and 250μm in diameter field of view

for OCT module, 81dB sensitivity, 13μm axial resolution, 15μm lateral resolution and 1.5mm per second imaging speed. The system was then tested by imaging AOM+DSS mouse model colon samples ex-vivo. OCT visualized microstructures of colon tissues including polyps and TPM showed cellular tubular gland structures and their distortion in polyps. The side-view endoscopic probe for combined TPM and OCT was successfully implemented and its performance was tested with mouse colorectal cancer model ex vivo.