Effects of various parameters on lateral displacement estimation in ultrasound elastography

Complementary to axial, lateral displacement and strain can provide important information on the biological soft tissues. In this paper, the effects of key parameters (i.e., lateral displacement, pitch, beamwidth, beam overlap and interpolation) on lateral displacement estimation were investigated, in simulations and homogeneous phantom experiments, using lateral rigid motion only to study its fundamentals separately from the effects of axial motion and 2-D deformation on lateral displacement estimation. The performance of the lateral motion estimator was evaluated by measuring its associated bias, jitter and correlation coefficient. Simulation results showed that the bias and jitter of the lateral displacement estimation and correlation coefficient of RF signals undergo periodic variations depending on the lateral displacement, with a period equal to the pitch. The performance of the lateral estimation was improved when a smaller pitch or a larger beamwidth, was used. The effect of the pitch on the lateral estimation on lateral displacement estimation was found to be greater than the beamwidth effect. Therefore, a smaller pitch is preferred when the beam overlap remains the same. The use of cubic spline, instead of linear interpolation, increases the correlation coefficient, and decreases the jitter, with the trade-off of increased bias. The results of the phantom experiments were shown in good agreement with the simulation findings, including the periodic variation of the performance with lateral displacement and effects of pitch, beamwidth and interpolation method on lateral displacement estimation. In conclusion, smaller pitch, wider beamwidth and spline interpolation were shown to be key in reducing the jitter error in the lateral displacement estimation.