Optical coherence tomography (OCT) is a non-invasive optical imaging technique that can be used to perform high-resolution cross-sectional in vivo and in situ imaging of microstructure in transparent as well as opaque biological tissues. Though resolutions as high as 1 to 5 m m have been achieved using conventional bulk optic bench-top systems in tandem with broadband light sources, the ability to use the same technology for commercial and clinical applications is restricted because of the prohibitive cost and cumbersome instrumentation. In a real clinical situation, a bulk-optic configuration is often not the most appropriate for an OCT system.
In our approach to realize a practical OCT system, we propose and demonstrate a novel, low maintenance, low cost, lightweight, and compact OCT system using an all single mode fiber (SMF) autocorrelator (Optiphase, Van Nuys, CA) based scanning system. The all-SMF autocorrelator based interferometer provides an accuracy comparable to bulk optics systems, and it could serve as a new technology to realize low cost and reproducible OCT instrumentation for commercial applications. The main advantage of this OCT system is that there is no separate arm for reference signal as the reference is derived from the partial back reflection at the end of the probe arm.
Fig. 1. Comparison of Michelson and Autocorrelator configurations. a.) Typical Michelson interferometer based OCT system. b.) The autocorrelator based OCT system with the above configuration was used in tandem with a translational stage to obtain 2-dimensional cross-sectional OCT images.
Preliminary Results:
To demonstrate imaging of a non transparent sample, we performed two dimensional cross sectional OCT imaging of an onion sample. The resolution of our OCT system is 20 µm (lateral) × 16 µm (longitudinal). Although the resolution is sub-optimal due to the limited bandwidth of the SLED source, and focusing limitations of GRIN lenses, the boundaries of the onion cellular structure can still be identified. The image size is 400 × 180 pixels, covering an area of 1.5 × 1.8 mm. Fig 2 also shows the OCT image of the thin layer structure of the transparent peel of an onion sample. It also shows a clearly distinguishable cross-sectional image of striated fibrous structure in the onion sample.
Fig 2. Acquired OCT images of onion samples. Resolution of the OCT images is 20 µm (lateral) × 16 µm (longitudinal). A) Boundaries of the cellular structure in the onion sample can be seen in top two layers. B) Air gap due to thin transparent onion peel layer on the onion sample can be observed (a). B) OCT image of fibrous structure in onion (b) and C) Corresponding magnified photograph of the same sample.
The advantages of having the flexibility in using interchangeable probes of arbitrary length can make it an extremely useful technology for Endoscopic OCT imaging. We are also working towards developing special lens probes designed for an optimum back reflection reference signal to optimize the sensitivity and resolution of the system. Overall, this technology may significantly reduce the cost of commercial OCT systems because of its simple, low cost, and robust all-fiber design.
References:
U. Sharma , N. M. Fried, J. U. Kang, and J. Bush, “Optical coherence Tomography based on an all-fiber autocorrelator using probe-end reflection as reference,” presented at the CLEO/IQEC 2004, CWJ3, San Francisco, California, USA, 16-21 May 2004.
J. Bush, P. Davis, and M. A. Marcus, “All-fiber optic coherence domain interferometric techniques,” Proc. SPIE 4204A-08, (2000).
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