| The mechanical properties of biological tissues have great significance for researching,diagnosis and therapy of diseases.However,the structure of biological tissues are relative complicated and it is very difficult to test the internal full-field mechanical properties.Digital volume correlation（DVC）method depends on three-dimensional imaging technique and can make the non-contacting internal full-field displacement and strain testing come true.Optical coherence tomography（OCT）is a high-resolution three-dimensional imaging technique.If it is combined with DVC technique,it will realize the high-resolution full-field three-dimensional testing for internal mechanical properties of biological tissues.This dissertation studied the experimental technique of internal full-field deformation testing for biological tissues combined with OCT and DVC,and realized solving the elastic parameters quantificationally combined with the virtual fields method（VFM）.The main work and results are as follow:Above all,a high-accuracy compression loading equipment has been designed,which realized quantificational testing of forces and displacements during the loading process.An experimental system which is adapt to testing the static compression of biological tissues has been integrated combined with the loading equipment and an existing OCT system in the laboratory.The optical path and the parameters of data aqusition have been optimized;a 3D OCT scanning protocol and a scheme for improving correlation of images are proposed through theoretical analysis and experimental verification.Furthermore,a DVC algorithm based on an inverse compositional Gauss-Newton（IC-GN）has been written and a method using course research to determine the initial values of displacements has been proposed so that the accuracy has been improved.The accuracy of the algorithm has been verified by simulation experiments.The sensitivity and accuracy of the test system based on OCT system have been verified by experiments.The results of testing the stationary objects show that the sensitivity of the system is 0.3μm for displacement tests;is 9×10-4 for strain tests.The results of testing for the rigid body displacements of objects and the experimental results of pressure on a homogeneous body show that the accuracy of the system is 3.4%for displacement tests and is 9.7%for strain tests respectively.The3D displacements and strains of a chicken breast tissue under compression were obtained using this system.Finally,to solve the elasticity modulus quantificationally an inversive method using the VFM and the three-dimensional strain fields tested by OCT and DVC has been proposed.The accuracy of the method combined with VFM and DVC of testing the elasticity modulus of materials is 2.8%,which has been verified by a simulation experiment.Compression tests have been done for a homogenous phantom and a double layer phantom respectively using the experimental system combined with OCT and DVC and the VFM.The three-dimensional deformation fields,elastic modulus and Poisson’s ratio of inside bodies have been acquired.The new experimental technique,combined with OCT and DVC,proposed in this dissertation can test the internal full-field three-dimensional deformation of biological tissues.The elastic modulus of a homogenous material can be acquired by the VFM with high accuracy.Although the error of testing the elastic modulus of the composite material is relatively big,it is feasible for quantificational testing the mechanical properties of heterogeneous materials with high accuracy through further experimental controlling,image processing and more accurate algorithm.The research results in this dissertation not only enriched the new technology of experimental mechanics but also provided a new testing method for biomechanical tests. |
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