Direction of arrival filters for improved aberration estimation.

Successful adaptive imaging requires accurate measurements of the aberration profile across the array surface. Two-dimensional spatial filters are used to obtain more accurate estimates of aberrating layers by suppressing wavefronts emanating from off-axis scatterers. Application of these filters to the rf signals of the individual elements rejects wavefronts arriving from angles other than the look direction of the array and results in an increase in element-to-element correlation. Spatial filtering reduced the amount of error in the measured aberration profiles and adaptive spatial filtering further improved the estimates. The improvements in aberration estimation obtained with these methods are verified using simulations and experiments in tissue-mimicking phantoms. The technique is applied to signals obtained from in vivo human thyroid.