Method for adaptively filtering doppler signals using a complex time domain filter

DETAILED DESCRIPTION The present invention relates to a time domain technique which implements an adaptive wall filter to improve imaging of low-velocity blood flow by removing from Doppler signals those signals associated with slowly moving scatterers.
Adaptive wall filtering is performed on basebanded data using a complex time domain filter which distinguishes positive and negative frequencies.
The center frequency and bandwidth of the complex time domain wall filter are selected in accordance with estimates of wall parameters obtained using an autocorrelation technique or any other conventional technique for measuring a tissue motion parameter.
In particular, an autocorrelation estimator can be used to estimate wall velocity and wall variance.
The wall velocity estimate determines the wall signal center frequency; the wall variance estimate determines the wall signal bandwidth.
The complex filter coefficients selected are those which will center the complex notch filter on the wall signal center frequency and set the cutoff frequencies (measured from this center frequency) to match the wall signal bandwidth.
An alternative implementation of the invention allows manual selection of the complex notch filter bandwidth, while the autocorrelation-estimated wall velocity determines the complex filter center frequency.
An object of the invention is to employ a time domain technique which implements an adaptive wall filter for imaging low velocity blood flow.
While the features of the invention believed to be novel are set forth in the appended claims, the invention itself, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: