Study Of Key Techniques Of Swept Source Optical Coherence Tomography For Imaging Of Human Skin Microvasculature

In clinical medicine,images of vascular distribution in tissues are useful in the diagnosis of diseases.For capillary imaging,the required accuracy cannot be achieved by conventional imaging methods,such as X-ray computed tomography(X-CT)and magnetic resonance imaging(MRI).At present the feasible methods for high resolution imaging of microvascular in vivo include the confocal fluorescence microscopy(CFM)and optical coherence tomography(OCT).CFM needs the injection of harmful fluorescent agent,and has short imaging depth for clinical application.Due to its advantages of non-invasive,high resolution and fast imaging,OCT has the great potential in microvascular angiography area.In this thesis,the key technical issues of exploiting OCT technology to image the human microvasculature were studied.The main work and innovations include the following:First,a handheld swept source OCT(SSOCT)system was designed and built for human skin imaging in real time.The measured value of the longitudinal resolution of the system is7.9?m,which is approximately consistent with the theoretical value of 7.1?m.The maximum imaging depth in the air is 3.2mm,and the system sensitivity is 101 d B.A phantom experiment and several in vivo experiments results demonstrate that the handheld SSOCT system has the capability of generating images of microscopic structures and microvasculatures in real time in vivo with high quality.Second,in order to improve the SNR and spatial resolution of human skin microangiography,a differential standard deviation of log-scale intensity(DSDLI)based optical coherence tomography angiography(OCTA)has been proposed for calculating microvascular images of human skin.The DSDLI algorithm calculates the standard deviation(STD)in difference images of two consecutive log-scale intensity based structural images from the same position along depth direction to contrast blood flow.The en face microvascular images were then generated by calculating the standard deviation of the differential log-scale intensities within the specific depth range,resulting in an improvement in spatial resolution and SNR in microvascular images.The SNRs of signals of flowing particles are improved by 7.3d B and 6.8d B on average in phantom and in vivo experiments,respectively,while the average spatial resolution of images of in vivo blood vessels is increased by 21%.Third,in order to improve the signal-to-noise ratio and contrast of retinal imaging,a differential phase standard-deviation(DPSD)-based optical coherence tomographic(OCT)angiography(OCTA)technique has been proposed to calculate the angiography images of the human retina.The standard deviation was calculated along the depth direction on the differential phase image of two B-scans to contrast dynamic vascular signals.When compared to other three common OCTA algorithms,it's showed that the DPSD achieved improved image contrast and higher sensitivity.Furthermore,we also found the improved signal-to-noise ratio and contrast-to-noise ratio of 1.6d B and 0.5d B,respectively,in large scanning range images.Fourth,in order to measure the blood flow accurately and suppress the speckle noise,a two-dimensional(2D)micro-electro-mechanical system(MEMS)-based,high-speed beamshifting spectral domain optical coherence tomography(MHB-SDOCT)has been proposed for speckle noise reduction and absolute flow rate measurement.By combining a zigzag scanning protocol,the frame rates of 45.2Hz for speckle reduction and 25.6Hz for flow rate measurement are achieved.Phantom experimental results have shown that 91% of speckle noise in the structural images can be reduced and a precision of 0.0032?l/s is achieved for flow rate measurement.In-vivo experiments on human skin and chicken embryo were also implemented to further verify the performance of speckle noise reduction and flow rate measurement of MHB-SDOCT.Finally,a SSOCT and fluorescence dual-mode imaging system was built and egg embryo experiments were carried out on that.The experimental results proved the feasibility of this system to monitor the changes of cell metabolic state and blood flow state during the process of Photodynamic Therapy(PDT).