Research On Measurement Of Blood Flow Shear Stress Using Optical Coherence Tomography

Optical coherence tomography(OCT)is a new medical imaging technology,which has the advantages of no radiation,non-contact,fast imaging speed,high-resolution and high cost performance.Both the spectral-domain OCT(SD-OCT)and the time-domain OCT(TD-OCT)take the Michelson interferometer as the core.Compared with the TD-OCT,the SD-OCT has a significant improvement in imaging speed,signal-to-noise ratio and sensitivity,and provides a powerful tool for ophthalmic disease diagnosis and early detection of vascular diseases.This thesis first introduces the theory of the SD-OCT and its structure;Elaborates the superiority of OCT over traditional medical imaging technology;Point out the advantages of OCT in studying blood flow velocity and blood flow shear stress;Analyzing the spectral signal of OCT,the spectral signal is divided into effective signals and interference signals;Discusses the main parameters of evaluating system performance.In this research,the spectral domain OCT with fast imaging speed and high resolution is used,and the optical path design and system structure are introduced.Under the action of the scanning system and the spectrometer,the spectral signal is collected and transmitted to the computer.After preprocessing such as DC removal,dispersion compensation,and background noise removal,the OCT image is reconstructed.Introduce how to construct the phantom experiment platform.Finally,the SD-OCT is applied to the measurement of blood flow velocity and blood flow shear stress.Phase shift wrapping and the noise of phase shift are the two main factors affecting the measurement of blood flow velocity and blood flow shear stress.Aiming at the phase shift wrapping image,a new phase shift unwrapping algorithm is adopted.However,this algorithm has certain limitations under the conditions of high noise and high-speed blood flow.Aiming at the defects of the phase unwrapping algorithm,a complex domain wavelet average noise reduction algorithm is proposed to reduce the noise of phase shift image.In order to verify the effectiveness of the proposed algorithm,simulation experiments and phantom experiments are conducted respectively.The results show that the proposed algorithm can not only improve the measurement accuracy of the phase shift of blood flow,but also overcome the noise sensitivity of the phase shift unwrapping algorithm.And the measurement range of velocity and shear stress has been increased to 90.2%,which provides a new method for high-speed blood flow and shear stress measurement.