A convergence index filter for vector fields and its application to medical image processing

It often happens in medical image processing that shadows with very weak contrast must be handled. When an ordinary difference filter is applied, shadows with a strong contrast other than the target shadow give a disturbance signal, making it difficult to extract the desired region embedded in the disturbance-producing shadows. This paper notes the directions of the gradient vector in the image and discusses a filter which can detect objects with high sensitivity based on the direction distribution. In this paper, the convergence index of the vector is generally defined, and a general expression for the convergence index filter which can be applied to both 2D and 3D images is presented. Specifically, the iris filter and the line convergence index filter are considered, and their responses are analyzed, together with their relations. An application to the actual medical image is presented, demonstrating the effectiveness of the idea. (c) 2006 Wiley Periodicals, Inc.