Study On Optical Coherence Elastography Technique Based On Shear Wave Loading

Histopathological changes of biological tissue are often associated with changes in mechanical properties.Lesions usually have higher Young's modulus than normal tissue.Therefore,biomechanical properties measurement is essential for the development,progression,diagnosis and treatment of various diseases.However,biomechanical testing techniques mainly rely on traditional tensile-compression tests,which can not meet the requirement for highly accurate measurement of biomechanical properties of complex tissue.With the development of medical imaging technology,optical coherence elastography(OCE)has emerged.Shear wave OCE has the potential advantages of nano-scale deformation resolution,millimeter-scale penetration and high imaging speed.However,as a new technology,the shear wave OCE technique needs to be improved in experimental methods,algorithms for mechanical properties extraction and results verification.This thesis aims to propose a new method for biomechanical testing,which is to develop an easy to use shear wave OCE technology to measure the tissue elasticity quantitatively with high accuracy.Firstly,the hardware of a shear wave OCE system was built,which includes a pulsed shear wave loading system of piezoelectric stack excitation and a swept source optical coherence tomography(OCT)system.Software was developed in Labview and Matlab to synchronize the shear wave loading and OCT scanning,and to acquire and process data.Secondly,a method of detecting the time of shear wave propagation was proposed based on the shear wave propagation theory and OCT phase analysis.Then the shear wave velocity was calculated by dividing the propagation distance by the propagation time,from which the Young's modulus of the tissue can be obtained.The measurement accuracy was verified to be about 98.5%,by comparing with the results of tensile tests.Finally,the shear wave OCE system was applied to measure the Young's modulus of skin in vivo.Moreover,a four-dimensional(three-dimension and time)data acquisition mode and its corresponding data processing method was proposed to image the elastic properties of heterogeneous tissue and visualize the shear wave propagation.The shear wave propagation was detected by the pulsed shear wave OCE from the OCT phase changes.However,the phase change needs not to be calculated accurately,which lowers the requirement for phase stability of the OCT and steady testing environment.The loading and testing of the pulsed shear wave OCE technique are simple and easy to use,which avoids cutting or clamping of the tissue specimen.This study provides a new technological tool for the elastic testing of biological tissue.It can be further developed to measure the nonlinear elastic properties of tissue with complicated structures in combination with advanced biomechanical theories.This pulsed shear wave OCE technique also has the potential to be translated to the bedside to aid the diagnosis and treatment of skin diseases.