| Optical Coherence Tomography(OCT)is a high-resolution,non-invasive biomedical imaging technique.As a functional extension of OCT technology,OCT vascular imaging technique can further extract blood vessel distribution and blood flow velocity information in tissues.It has become an indispensable tool in the research of vascular-related diseases and clinical ophthalmology.Compared with the previous two generations of implementation,swept source OCT(SS-OCT)has higher sensitivity and imaging speed.and is an ideal vascular imaging platform.However,SS-OCT in in vivo blood vessel imaging is suffered from unstability of the swept laser output and bulk motion of living samples,which may introduce noise and artifacts in the blood vessel image.and reduce the sensitivity;On the other hand,data size of high-speed SS-OCT is extremely large.whieh hinder the achievement of real-time imaging,In respect of the problems above.the research works in this article includes:(1)An SS-OCT system was designed and built with a center wavelength of 1310 nm.and sensitivity of 101.03 dB;Based on the Mach-Zehnder interferometer(MZI).the polygon-scanner-based laser and MEMS-based laser were evaluated.We found that in addition to the unstable phase of the polygon-scanner-based laser,there is also the problem of periodic fluctuations in the swept range.Two polygon-scanner-based lasers showed the maximum relative changes of 7.76%and 7.02%.respectively:Based on the reference MZI signal with maximum swept range,we proposed a correction method without truncating the OCT interference signal.After correction,the phase sensitivities of the two swept lasers are 0.0039 rad and 0.0020 rad.which are close to the theoretical limits under phase stability,and successfully separated dynamic and static particles in the simulated blood vessel experiment.(2)For the repetitive bulk motion like cardiac and respiratory motion of living samples.a model of the maximum normalized cross-correlation value and the inter-plane displacement dy is established.The coefficient of determination R2 of the model for mouse skin and cerebral cortex is not less than 0.9958 and 0.9974,respectively.Then.the relationship between the dy value and the relative sensitivity of blood vessels is established.Next,corrupt angiograms filtering,reorganization.sub-pixel registration are performed on the data of repeated three-dimensional volumes,and finally obtain the OCT angiography en face image of the mouse skin with less noise.(3)In order to realize real-time imaging processing,the calculation amount of the above method is optimized first to reduce the computation.Then the processing steps,such as laser instability correction.complex OCT signal reconstruction,blood vessel information extraction,bulk motion measurement.and noise elimination are implemented in a graphic processing unit(GPU)with the parallel processing speed of 498 B-Scan/s.Finally,the high-sensitive blood vessel real-time imaging mouse cerebral cortex angiography en face image was obtained.(4)An SS-OCT with a center wavelength of 1 micron was built.Based on the above-mentioned real-time processing platform,the blood vessel signals in the human retina that close to the optic disc and macular region were successfully extracted.Through the study,the noise in angiography is greatly reduced,and high-sensitive real-time SS-OCT in vivo vascular imaging is realized,which may provide enormous value for further research on biomedical researchs and applications. |
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