Performance comparison of rigid and affine models for motion estimation using ultrasound RF signals: Simulations and phantom experiments

Rigid model-based and non-rigid model-based methods are two main groups of space-domain methods of tissue motion estimation. Affine model is one of the commonly used non-rigid models. The performances of the rigid model and affine model have not been compared on ultrasound radio-frequency (RF) signals. In this study, three methods, i.e., the normalized cross-correlation method with rigid model (NCC), the optical flow method with rigid model (OFRM) and optical flow method with affine model (OFAM), are compared using ultrasound RF signals, rather than B-mode images used in previous studies. Simulations and phantom experiments are conducted to make the comparison. The results show that the affine model-based method (i.e., OFAM) obtains the lowest root-mean-square error (RAISE) or registration error among all the methods. The affine model is demonstrated to be superior to the rigid model in motion estimation based on RF signals.