The Lee filter, in particular, was used. The Lee filter uses blurring based on the mean and variance of local regions to denoise the image.
Below: CP ultrasound of a 12 mm target at +6 dB from the background. Bottom is the Lee filter using a window size of 7x7 applied to an eREC-FC ultrasound image of the same target. Bottom shows the filter's effects on the CP image in an overlaid manner.
Local Statistics Filters Results