Speckle noise reduction for ultrasonic images

This paper presents a method to enhance ultrasonic images that are commonly plagued with a special type of acoustic noise called speckles. To reduce the noise effect, filters such as the weighted median filter, adaptive trimmed mean filter, two dimensional weighted Savitzky-Golay filter (2D-WSGF) have been studied. We have found that 2D-WSGF has the best image restoration quality. Based on the least squares fitting of a polynomial function to image intensities, 2D-WSGF can preserve edges while performing noise reduction. However, 2D-WSGF requires a relatively large fixed mask, which inevitably incurs unnecessary computation cost. In this paper, a variable-mask approach is presented to improve the computation performance and the restored image quality of the 2D-WSGF. Advantage of using variable mask size is that computation time for filtering can be greatly saved at the expense of relatively little computations needed for detecting bumpy regions and estimating the corresponding mask size.