Displacement And Strain Estimation In Ultrasound Elastography

The purpose of ultrasound elastography is to identify lesions through the hardness of tissue recovered from ultrasonic data. Nowadays, ultrasound elastography has been considered to have great potential in clinical applications. Tissue motion estimation from ultrasound image sequences plays a central role in ultrasound elastography. Therefore, the performance of tissue motion estimation is of significant importance. First, the computational cost of estimation method determines if it can be implemented in real-time so that it can be used clinically. Also, it is necessary to recover a full displacement field (axial and lateral components in 2D situation) in order to describe the physical nature of the strain tensor or elastic parameters.A phase-shift estimation method is presented in this thesis to accurately estimate axial component of tissue displacement field in ultrasound elastography. The phase aliasing problem is solved after using prior estimates of displacement field, and the numerical complexity is largely reduced.To accurately obtain the lateral components of tissue displacement field, this thesis presents a bio-mechanical model constrained filtering framework to recover a fine and full displacement field in ultrasound elastography:after integrating the bio-mechanical model constraint into the state space equation, the axial and lateral displacement components in a fine scale are recovered from the noisy displacement measurements through a robust H∞filter. All the strain components can be calculated by applying a gradient operator on the recovered displacement field.