Nonlinear ultrasonic image processing based on signal-adaptive filters and self-organizing neural networks

Two approaches for ultrasonic image processing are examined. First, signal-adaptive maximum likelihood (SAML) filters are proposed for ultrasonic speckle removal. It is shown that in the case of displayed ultrasound (US) image data the maximum likelihood (ML) estimator of the original (noiseless) signal closely resembles the L₂ mean which has been proven earlier to be the ML estimator of the original signal in US B-mode data. Thus, the design of signal-adaptive L₂ mean filters is treated for US B-mode data and displayed US image data as well. Secondly, the segmentation of ultrasonic images using self-organizing neural networks (NN) is investigated. A modification of the learning vector quantizer (L₂ LVQ) is proposed in such a way that the weight vectors of the output neurons correspond to the L₂ mean instead of the sample arithmetic mean of the input observations. The convergence in the mean and in the mean square of the proposed L₂ LVQ NN are studied. L₂ LVQ is combined with signal-adaptive filtering in order to allow preservation of image edges and details as well as maximum speckle reduction in homogeneous regions