We report the design and validation of a novel ball lens-based imaging catheter based on dual-clad fiber for frequency-domain fluorescence lifetime imaging microscopy (FLIM) of atherosclerosis. The illumination and collection performance of the catheter endoscope was modeled and optimized with the ray-tracing program Zemax. A 1.55-m-long dual-clad fiber was spliced with a short length of coreless fiber, and then heated and polished to fabricate the angled ball lens. The fiber endoscope was enclosed in a torque cable and had a diameter of 2Fr. The catheter was affixed to a custom built lensless rotary joint which had high coupling efficiency (>90%) over a broad spectral range, accommodating both the UV (375 nm) excitation and the broad fluorescence emission (385 nm - 600 nm). The computer controlled rotary joint and translation stage for pullback imaging can routinely achieve rotation rates of 6000 rpm. The endoscope has two configurations depending on different illumination methods. Lateral resolution was improved more than twice by illuminating the core instead of the inner cladding, while SNR decreased due to higher attenuation of the core. Experiments conducted using a resolution target demonstrate a lateral resolution 80 μm at 1 mm lens-to-sample distance. Experiments conducted using a fluorescein phantom and a segment of ex vivo human coronary artery demonstrate the system performance for fluorescence lifetime imaging with pullback velocities of >10mm/s. This study demonstrates the novel design of a ball lens-based FLIM catheter system to record fluorescence in a continuous helical scanning method across broad-spectral emission bands.
Xi Chen, Wihan Kim, Michael J. Serafino, Zheng Tan, Brian Walton M.D., L. Maximilian Buja M.D., Jessie Adame M.D., Javier A. Jo, and Brian E. Applegate, "Design and validation of the ball lens-based intravascular catheter for fluorescence lifetime imaging microscopy of atherosclerosis (Conference Presentation)," Proc. SPIE 10471, Diagnostic and Therapeutic Applications of Light in Cardiology 2018, 1047102 (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287447.5751467318001.
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