Design of a dual-modality imaging system using optical coherence tomography and fluorescence lifetime imaging microscopy for anatomical and biochemical diagnosis of tissue
Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XIV
Both morphological and biochemical changes occur in a diseased tissue. As a result, tissue optical response changes with the progression of disease. A single optical imaging modality can assess either morphological or biochemical changes. In order to investigate the development of a disease in detail, both of these characteristics need to be probed simultaneously. Therefore, researchers have been interested in combining different imaging modalities that can provide complementary, morphological
... ary, morphological and biochemical images. This dissertation focuses on the development of dual-modality systems that incorporate Optical coherence Tomography (OCT) and Fluorescence Lifetime Imaging Microscopy (FLIM) for simultaneous characterization of tissue morphology and its biochemistry. In the first phase of the research, we combined spectral-domain OCT with FLIM that is designed for endogenous emission acquisition. The operating wavelength for OCT and FLIM were 830nm and 355nm, respectively. The maximum field of view (FOV) was 4mmx4mm. The combined system was used to image hamster cheek pouch model for oral cancer in vivo and postmortem human coronary arteries with atherosclerotic plaques ex vivo. Their morphological and endogenous emission images correlation was studied. The evaluation was equivalent to their histopathological analysis. In the second phase of this research, we built a bench-top prototype that comprised of swept source OCT (SSOCT) and a FLIM system with the capability to iii characterize endogenous and exogenous emissions simultaneously. The swept laser had a sweep rate of 50 kHz and the center wavelength was at 1310nm. FLIM utilized lasers with wavelengths 355nm and 532nm to excite endogenous and exogenous fluorophores, respectively. The maximum FOV was 16mmx16mm. With this system, OCT-FLIM images of a Watanabe rabbit aorta, which was non-specifically tagged with Alexa Fluor 532, were acquired ex-vivo. The results appraised the ability of the system to simultaneously probe the sample's structure, its endogenous emission and the exogenous fluorescence of the dye tagged to it. We hypothesize that the OCT-FLIM imaging tool adds a potential to study the activities of important non-fluorescing molecules in an artery while relating the analysis to its morphology and biochemistry. iv DEDICATION To my parents. v ACKNOWLEDGEMENTS I offer my sincere gratitude to my advisors Dr. Brian Applegate and Dr. Javier Jo for introducing me to this prodigious field of research, which has ended up becoming my fervor. I am grateful for their guidance and support during my journey at Texas A&M University (TAMU). I must say I learnt every aspect of optical imaging system design, development, testing and troubleshooting, while working closely with Dr. Applegate. Likewise, Dr. Jo helped me a lot in assimilating animal studies, sample preparation for imaging as well as histopathological processing, and the motivation to such research. I always admired their depth of knowledge in many sectors of science and engineering, and their teaching approach in lab. I would like to thank Dr. Kristen Maitland for helping me understand the fundamentals of optics in her course -Biophotonics. Also, her method of well-organized research has inspired me. I am thankful to Dr. Ohannes Eknoyan for teaching one of the most interesting classes, Optoelectronics, during my graduate studies. I would also like to thank him for his time and energy to serve on my committee. I would also like to appreciate Dr. Jesung Park for his tremendous guidance on system synchronization and testing, writing codes for image acquisition and processing, and animal studies. Also, my special thanks goes to all other former and current team members of this OCT-FLIM project-Paritosh Pande, Dr.