Dual OCT/spectroscopy system for identification of vascular pathology

Abstract

An imaging system combining optical coherence tomography (OCT) and laser induced fluorescence (LIF) spectroscopy has been built. The system produces both cross-sectional images of tissue structure and fluorescence spectra of surface features. The system has been used to image ex vivo canine aorta with the goal of identifying differences in anatomy and fluorescence between normal canine aorta and canine aorta with an endovascular stent graft. The OCT portion of the system is based on a fiber optic Michelson interferometer. The OCT system measures the intensity of back-reflected infrared light in order to build up images of the subsurface tissue structure. The LIF portion contains a helium cadmium laser, which is used to excite fluorescence in the tissue. Excitation light is guided to the tissue and fluorescence is captured by the addition of a cold mirror into the OCT sample arm optics. The wavelength of 442 nm emitted by the laser is well suited for exciting the main fluorophores in aorta, namely elastin and collagen. It is expected that canine aorta with and without a stent will differ in the relative composition of these fluorophores and can thus be differentiated using LIF spectroscopy. This group has previously used OCT to measure the thickness of different layers in the arterial wall of a porcine model of atherosclerosis. In this paper, we investigate the ability of our combined system to differentiate normal from implanted canine aorta by combining OCT with spectroscopy. We note features of the endovascular stent graft in the OCT image and subtle differences between normal and implanted aorta in the LIF spectra.