Speckle Reduction Techniques in Medical Ultrasound Imaging

Effective speckle reduction is important for enhancing image quality and improving our understanding of medical ultrasound imaging. Various speckle reduction techniques, such as frequency compounding (SR-FC), spatial compounding (SR-SC), and post filtering (SR-PF), have been proposed. In SR-FC, uncorrelated sub-images, which are obtained by either varying the center frequency on transmission or by dividing the spectrum of radio-frequency (RF) signals on reception, are compounded to lower speckle. In SR-SC, the sub-images are acquired at different beam orientations at the expense of temporal resolution. On the other hand, in SR-PF, instead of compounding multiple sub-images, a specially designed spatial filter, e.g., Laplacian pyramid-based nonlinear diffusion, is applied to a single image. These techniques can be integrated together to maximize the effects of speckle reduction. This review briefly introduces the principles behind three speckle reduction techniques and describes their own strengths and weaknesses. Finally, some clinical examples of speckle reduction techniques are presented.