The Finite Element Method Simulation Analysis Of Ultrasound Elastography

Elastic modulus' change of the biological tissue is usually related to the pathological phenomena, therefor, the elasticity information of the biological tissue have a very important reference value to the disease diagnosis. However, traditional medical imaging methods, including x-ray imaging, ultrasonic imaging (US), magnetic resonance imaging (MRI), computed tomography (CT), etc, can not provide the elasticity information of the tissue directly. In clinical, usually using palpation method to obtain lesions of the elasticity information. But, the palpation method has some limitations, on the one hand, it is affected by the subjective experience of the doctor, on the other hand, this method can only check the surface tissue, and can not be tested the deep tissue thoroughly, moreover, it is difficult to find the small lesions. 1991, Ophir et al proposed ultrasound elastography method, conducting a method to estimate the distribution of the tissue's elastic modulus quantitatively and image. In recent years, ultrasound elastography has become a research hot spot in medical ultrasound imaging areas, it has very important clinical value, and has a broad application prospect.Ultrasound elastography of the organization often uses static / quasi-static motivate method. This method uses a probe or a probe-extrusion plate device compressing the organization along the vertical(axial), imposing a small strain to the tissue (such as 1% of magnitude), then collecting the ultrasound signals(RF signals) or the envelope signals before and after compressing the tissue separately, using the cross-correlation method to analysis these signals, to estimate the displacement distribution at different positions of the tissue, and get the tissue's strain distribution.In the process of the ultrasound elastography's two-dimensional and three-dimensional simulation, finite element analysis method has a very important role. In the course of elastography, in order to receive the compressed ultrasonic echo, it must be get re-distribution of the compressed scattering particles of the tissue, which requires the help of finite element analysis to get the numerical solution of elastic problem. Finite element simulation method can simplify the complex elastomer to a collection of some limited units, and can get the exact approximately solution of the complex elastomer's internal particle's location change. In the simulation experiment, use the results of finite element analysis method comparing with the results of the ultrasound elastography, it can estimate the good or bad effect of ultrasound elastography, and comparing the merits of imaging methods. Using finite element method to simulate the compression tissue, can study the impact that a variety of mechanical parameters and geometric parameters of the soft tissue in ultrasound elastography. At present, about the research of the internal stress and strain distribution at the tissue compression in the ultrasound elastography, it mainly has two two methods to analysis. The one is using finite element method, combining with the elasticity theory, to study the simulation of the compression organization; Another method is based on the elasticity theory, combining with the practical experience formula, derive the internal stress and strain distribution of the compression tissue, give the analytic expression of the stress and strain distribution directly.This paper use the first analysis method, that is, based on the elasticity theory, using finite element method for compression tissue's computer simulation study, come to the distribution of internal displacement and strain distribution, for the follow-up study of ultrasound elastography providing important parameters and basis. The specific work of this paper including:1. Based on the assumption of the tissue in ultrasound elastography, based on the finite element analysis principle, ues finite element simulation tools, established uniform tissue model, haven the finite element mesh map of the uniform tissue model.2. Simulate the case that in uniform tissue distributing foreign objects(simulate lump) with different elasticity contrast, select imposing the appropriate boundary conditions, come to its displacement distribution and strain distribution map which under the conditions of the uniform tissue containing foreign objects.3. Explore the case that under different boundary conditions, when the foreign object and the tissue's elasticity contrast is different, get the strain distribution in x-direction that in the case different elasticity contrast.4. Under the case that in the same boundary conditions and elasticity contrast, study the strain distribution map in x-direction when the tissue distributing different foreign objects, which results providing some reference value for the further theoretical and experimental studies.