Stick based Non-local Means Filter for Speckle Reduction in Ultrasonic Images

Harbin Institute of Technology, China

^a Corresponding author: sunmingjian@hit.edu.cn

Abstract

Accurate visualization and quantification of human structure is an important prerequisite for a number of clinical procedures. Specially, a current challenging issue in medical ultrasonic images is the problem of speckle reduction while keeping the structure and texture information. A stick based non-local means filter is proposed in this paper. An asymmetric stick filter kernel is firstly defined by decomposing the rectangle search window of non-local means (NLM) filter into a set of line segments with variable orientations. Then, the sticks which used to search for similar pixels are selected by a normalized variance function. Finally, the weighted sum of averages of the similar pixels searched along each selected stick is used to produce the filtered image. With the introduction of the asymmetric stick, it is possible to implement the NLM filter in an oriented diffusion way. Experiments of synthetic and real clinical ultrasound images show that the stick based NLM filter performs effectively in suppressing speckle while pre-serving resolvable structures and even enhancing linear features such as the edges.