In conventional optical coherence tomography (OCT) the resolution of the image is dependant on the spectral width and center wavelength of the light source. We investigate whether the application of chromatic analysis techniques and Gaussian peak fitting can provide an improved resolution to OCT images. OCT signals were simulated mathematically and analyzed to observe interference effects in the signal when considering two surfaces separated by less than the coherence length of the source. Chromatic analysis was then applied to identify the component interferograms within the signal. The peaks of these component interferograms were then found by fitting Gaussian peaks to the signal. Images of air wedges and onion slices were analyzed and improved resolution was shown in both cases. This work shows the potential for the use of chromatic techniques in improving the resolution of OCT images in tissue.
An optical fiber based low coherence interferometer for measuring the Epithelium thickness of Bronchial tissue, for early diagnosis of Carcinoma in situ, is presented. Previous simulation of laser induced fluorescence using an electromagnetic scattering model has extracted the relative permittivity value for the Submucosa and Epithelium layers indicating a difference of up to 0.14. The optical system presented here uses a low coherence source operating at 840 nm with a bandwidth of 30 nm, coupled into single mode optical fiber. A Fizeau cavity is formed between the fiber end and the tissue under investigation. A remote processing interferometer is used to monitor changes in permittivity between the different tissue layers. An initial experiment has demonstrated a sensitivity measurement of 40 dB for a permittivity difference measurement of 0.61. Preliminary results have shown that the discontinuity between the Bronchial Epithelium layer and its surrounding medium can be identified allowing the thickness of the Epithelium layer to be measured to an accuracy of 20 micrometers . Since interferometric noise contributions are only significant within the processing interferometer, the fiber optic Fizeau interferometer technique is a strong candidate for the development of an endoscope for the early detection of cancer within Gastrointestinal and Respiratory tracts.
Previous measurement by Qu et al, of laser-induced fluorescence in bronchus tissue are simulated using an electromagnetic (EM) scattering model. The EM parameters derived indicate that the changes in the epithelium thickness with carcinoma in situ can be detected with an optical radar process, hence providing an early detection of cancer. Further simulation using the EM model indicates various practical methods of extracting the thickness changes. These include frequency modulated continuous wave optical radar, multilaser continuous wave radar and low coherence interferometry. Initial optical experiments and calculations clarify which method is likely to lead to the development of endoscope instrumentation, but the availability of suitable optical components is a major consideration. Some early interferometry results indicate that a resolution of at least 40 micrometers can be readily reached for histological imaging. For 10 micrometers cell resolution, additional techniques are required.
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