A Method to Estimate Position Shifting Caused by Phase Aberration in Ultrasound Imaging

Phase aberration is the error caused by heterogeneous speed of sound in ultrasound images. Cross correlation methods are being explored to estimate the phase aberration, and therefore correct for it.  However, these methods only correct for the shape distortion of the image caused by phase aberration and do not take into account the shifting of the image that also takes place. A forward model has been developed to connect the phase aberration estimated using cross correlation methods and the true phase aberration when the focus point is located along the central axis of the probe. This paper builds on the previous forward model to account for off-axis focus points. A modified equation is proposed which accounts for each individual probe element's contribution towards shifting. This equation is then used to create a forward model connecting the true phase aberration to the estimated phase aberration for both on- and off- axis focus points. This model was validated using numerical simulations. The inverse model was then solved for the case where the phase aberration is due to an incorrect average speed of sound and the initial delay of the probe. This inverse solution was also validated using numerical simulations. The model was also tested on simulated speckle-generating phantoms  and experimental phantoms.