A Post -Filtering Technique for Autocorrelation Estimator in Realtime Color Flow Mapping Systems
A new post-filtering technique to eliminate the clutter signals for the autocorrelation mean frequency estimation (ACE) method that is most commonly used in detecting the Doppler shift in Color Flow Mapping (CFM) systems is presented. In the general two dimensional Doppler imaging environment, the complex input Doppler signals contain the clutter components even after clutter filtering, which results in the estimation error or the loss of the ability to detect the low speed flow. A post-filter, which is a zero-phase FIR filter, is added after the autocorrelator to further remove the clutter components. The additional computational amount required for the post-filtering increases with the filter length until it becomes equal to the length of the autocorrelation function of the clutter filtered samples but does not change after then. This is because that only two terms of the filtered autocorrelation function are needed for the mean frequency and variance estimation. Since the post-filter can have any large number of taps, it can be designed to have arbitrary responses and find many applications. One example of applying this new technique to dramatically reduce the effect of the clutter components is provided, which is venfied by computer simulation.
KeywordsAttenuation Autocorrelation Convolution Cross Correlation Acoustics
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