Optimized filters for dynamic RF echo blending in multiple focal zone imaging

For several practical and technical reasons related to e.g. computational cost, hardware complexity, sensitivity to motion artifacts, frame rate and SNR most medical ultrasound machines use a fixed focus on transmit and dynamic focusing and filtering on receive. To further improve image resolution, multiple focal zones may be used. The resulting A-lines are superimposed (blended) after envelope detection by means of depth dependent weighting. Due to this incoherent superposition, the spatial resolution of the resulting image can only reach the resolution of the images that were superimposed. To overcome the shortcomings of incoherent superposition we have developed a technique for coherent filtered blending of the echoes. In addition to echoes representing different transmit foci, echoes from neighboring beam lines may also be considered.