BIASED MOTION-ADAPTIVE TEMPORAL FILTERING FOR SPECKLE REDUCTION IN ECHOCARDIOGRAPHY

This paper describes a new fully motion-adaptive spatio-temporal filte ring technique to reduce the speckle in ultrasound images, The advanta ges of this approach are demonstrated in echocardiographic boundary de tection and in comparison with other techniques, The first stage of ma ny automated echocardiographic image interpretation schemes is filteri ng to reduce the amount of speckle noise, We show how the two-dimensio nal least mean squares (TDLMS) filter can be configured as a motion-co mpensated filter for a time sequence of ultrasound images that elimina tes the blurring associated with direct averaging, For an image corrup ted by multiplicative speckle noise, the mode of the intensity distrib ution approximates the maximum likelihood estimator, In consequence, t he temporal filter's output is biased towards the mode from the mean, using information contained within the speckle itself. A new adaptive algorithm for controlling the filter's convergence is also included, T o evaluate performance, application to simulated, phantom, and an in v ivo test sequence of the carotid artery are considered in comparison w ith other techniques, The effect of filtering on edges is of great imp ortance, as these are used by subsequent image interpretation schemes, Quantitative measurements demonstrate the effectiveness of the Biased TDLMS filter, for both noise reduction and edge preservation, Echocar diographic images have a high noise content and suffer from poor contr ast, Despite this challenging environment, the Biased TDLMS filter is shown to produce images that are better inputs for subsequent feature extraction. The benefits for echocardiographic images are highlighted by considering the problems of mitral valve analysis and extraction of the left atrium boundary.