Reviving and extending the mid‑field phase screen model for distributed aberration correction

Aberration is one the key sources of image degradation in handheld B-mode ultrasound imaging. Sound speed heterogeneities in human tissue induce path-dependent delays that result in spatially varying aberrations in the image. One of the earliest models for aberration was the near-field phase screen. This was later extended to a mid-field phase screen model by introducing an offset between the aberrating screen and the transducer surface. By introducing this offset, the mid-field phase screen model could capture the parallax in the aberrations observed in the image. However, a single mid-field phase screen cannot fully capture the aberrations caused by a spatially varying sound speed. In this work, we extend the mid-field phase screen model by placing phase screens at multiple depths and demonstrate its approximate equivalence to a full sound speed profile under a straight-ray assumption. Phantom experiments show a 51-62% improvement in point target resolution because of the proposed aberration model and correction scheme.