Identifying the mechanical properties of tissue by ultrasound strain imaging

A new elastography method is presented that images the mechanical properties of soft tissue. The tissue is externally vibrated over a range of frequencies simultaneously and the resulting displacement is recorded at multiple locations and time instants with a sequence of ultrasound images. Two methods are proposed for estimating the mechanical properties from the recorded data. In the first method, equations of motion are written for a tissue model of masses, springs and dampers. The equations are solved to identify the model parameters and construct an image. The second method performs a transfer function analysis of the tissue motion. The tissue properties are identified from the shape the of transfer function. Simulations show good performance of the new method compared with static elastography. Initial experimental results from homogeneous and layered tissue phantoms also demonstrate the ability quantitatively to image tissue stiffness. Preliminary results are obtained for viscosity and density estimation. Further work is needed to extend the formulation to 3-D and improve robustness of the viscosity and density estimates.