![]() Thus, the micron resolution could be realized by choosing the ultra-wide spectral bandwidth light source. In spectral domain OCT the axial resolution δ s is a function of the bandwidth of the light source Δ λ and the center wavelength λ 0,expressed by δ s = 4 ln 2 λ 0 2 ∕ π Δ λ . Its advantage should be the capability of in-vivo visualization and without the staining process. To visualize the comparable details acquired by the histopathological method, 3D imaging with cellular or subcellular resolutions along each dimension must be one of major topics in OCT. The histopathology to inspect the micro changes of tissue is still the current gold standard which has the molecular specificity with the staining. Nevertheless, the resolutions are insufficient to resolve the cellular or subcellular features associated with the fundamental changes of diseases. Conventionally, OCT is of ∼ 10 μ m axial resolution, ∼ 30 μ m transversal resolution and ∼3 mm imaging depth ,, which can provide 3D architecture morphologic information. In order to visualize 3D structure of the biological tissue the three parameters, axial resolution, transversal resolution and imaging depth attracted a lot of interest. It has shown great potential in clinical imaging, including ophthalmology, dermatology, cardiology and gastroenterology . Optical coherence tomography (OCT) is a label-free and non-invasive cross-section imaging technique based on the near infrared low coherence interference and endogenous scattering contrast . Finally, the experimental results are presented to demonstrate the accuracy and effectiveness of our model. For the EID defined by the micron axial resolution NA < 0.1 should be recommended, otherwise, the method to eliminate the effect of NA must be taken. 6 μ m, which is about ten times of the micron level resolution. The axial resolution could even be reduced to 11. A large NA, such as 0.4, would lead to multiple split peaks and severe side lobes in the axial PSF. Similar to the dispersion mismatch between the sample arm and the reference arm, the NA of objective lens does influence the axial resolution in the form of convolution. It limits the EID defined by the signal fall-off less than 500 μ m. Among all the parameters the focusing effect of objective lens affects the signal intensity most due to the fast broadening of the effective point spread function (PSF) incident on the photosensitive surface of detector. Based on the model, the parameters that influence the axial resolution, the signal intensity and the EID can be quantitatively analyzed. To this end, a theoretical model for the micron resolution spectral domain OCT was proposed with both the temporal coherence and the longitudinal spatial coherence considered. The resolution and effective imaging depth (EID) of spectral domain optical coherence tomography (OCT) are of great importance for visualizing the fine details of biological tissues.
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