Development Of Full Range Spectral Domain Optical Coherence Tomography

Optical coherence tomography (OCT) is a non-invasive biomedical imaging technology. Spectral domain OCT (SD-OCT) is the second generation of OCT, due to the advantages of high imaging speed, high signal-to-noise ratio and high-resolution, SD-OCT has been widely used in the field of ophthalmic imaging, materials testing, and angiography. SD-OCT detects spectral interferograms as a function of optical frequency and produces A-scan data by applying a Fourier transform to the acquired interference spectrum. However, the Hermite conjugacy of the A-scan data results in complex-conjugate artifact, which limits the imaging range of SD-OCT. In order to expand the imaging range of SD-OCT, we proposed two new methods to eliminate the complex-conjugate artifact. The main work and innovations are summarized as following::1、The development, principle and defect of the SD-OCT is described in detail. Several existing methods for the elimination of complex-conjugate artifact is introduced. The advantages and disadvantages of the linear B-M mode method is analyzed in detail.2、Full range optical coherence tomography without additional group delay based on spatial carrier frequency is developed. A grating takes place of the mirror in the reference arm of the conventional OCT system. Phase difference without additional optical path difference is introduced between adjacent A-scans. Spatial interferograms is obtained by applying transverse Fourier transformation upon the OCT signal. The coherent mirror image in the spatial interferograms is filtered. Then by inverse Fourier transform of the filtered signal, complex interference signal can be obtained. Finally a full range OCT image can be obtained after axial Fourier transform of the complex interference signal. The influencing factors of the spatial carrier frequency is investigated experimentally. The performance of the proposed full range optical coherence tomography method is validated by imaging of finger skin.3、The theory of the visibility control is analyzed. In order to control the shape of the Talbot band’s visibility, a series of simulations are done. And a system for full range imaging of the anterior segment is designed. Based on the Talbot band theory, the reference beam and sample beam irradiate in the different area of the grating. As a result, the maximum of the visibility moves to the area that we are interested in. Two high sensitivity image will be got by controlling two switches which can change the position of the reference plane and the corresponding position of maximum sensitivity. The full range OCT imaging will be obtained finally by the way of splicing two OCT imaging which reconstructed under two different switch modes.