Speckle reduction in pulse-echo ultrasonic imaging using a two-dimensional receiving array.

An experimental pulse-echo imager was developed for the purpose of reducing speckle in ultrasonic images. The system utilized a 64-element spherically focused segmented annuli array receiver with a common transmitter. Compounded images were formed using subapertures of varying size, shape, and overlap, and the speckle and resolution characteristics of the final images were observed. A pointlike scatterer was imaged to determine the resolution, point spread function, and sensitivity of the system along with a new measure called the resolution cell size. The response of the system was also simulated for comparisons. It was found that lateral resolution, and resolution cell sizes only gradually increased with a decrease in subaperture size and system sensitivity was not greatly diminished. Incoherent summation of signals from small groups of elements decreased the speckle noise by a factor of four while maintaining enough resolution to improve the image quality as measured by the CSR/d by a factor of almost two.