Quantitative reconstruction of tissue elasticity from vibrating ultrasound image sequences

The purpose of elasticity imaging is to map the mechanical properties of soft tissues, such as the elastic modulus, viscous modulus and Poisson's ratio. Of these, the most important parameter is Young's modulus because its change is often related to tissue pathology or, in the case of muscle, to physiologic processes. Quantitative reconstruction of elastic properties remains the most problematic aspect of virtually all methods of elasticity imaging. The objective of this work is to reconstruct the tissue elastic modulus from vibrating ultrasound echo sequences.; A method to estimate the 2-D vibration amplitude and phase fields from a vibrating ultrasound echo sequence is proposed. The meshed-based speckle tracking method previously developed is improved so that it is able to more accurately estimate displacements between two frames. A least square estimator is introduced to calculate the vibrational motion (amplitude and phase) from the displacements of ultrasound echo sequences. Traditional regularization is proposed to recover the dense motion field from the sparse motion of mesh grids.; A plane wave propagation model previously suggested is verified using finite element method (FEM) simulation and experiments on tissue-mimicking phantoms, but only for specific circumstances. The elastic modulus can be determined by taking the derivatives of the vibration phase when the viscosity is neglected at low vibration frequencies. However, the method was found not to be applicable to human thigh muscles.; A novel iterative forward approach is further developed to reconstruct the Young's modulus of soft tissues from measured vibration amplitude and phase fields. Elastic property reconstruction is formulated as a forward problem based on finite element theory. An arbitrary region of interest (ROI) is chosen for which Young's modulus can be reconstructed. The sensitivities of the results to Poisson's ratio, the damping coefficient (viscosity) and added noise are investigated using numerical simulation. Elastic property reconstruction is integrated with speckle tracking to provide a systems approach by which the elastic modulus can be reconstructed directly from vibrating ultrasonic echo sequences. The systems approach is verified using simulated speckle tracking data and using experimental data from tissue-mimicking phantoms and human thigh muscles.