Clutter rejection filters in color flow imaging: a theoreticalapproach

摘要

A general class of linear clutter rejection filters is described,ncovering the commonly used filter types including FIR/IIR filters withnlinear initialization, as well as regression filters, where the clutterncomponent is estimated by least square curve fitting. The filter can bendescribed by a complex valued matrix, and a frequency response isndefined. However, in contrast to a time invariant filter, the generalnlinear filter may create frequency components which are not present innthe input signal. This produces bias in the velocity and velocity spreadnestimates. It is shown that the clutter filter effect on thenautocorrelation estimates can be described by a frequency domainntransfer function, but unlike time invariant filters, the transfernfunction is different for each temporal lag of the autocorrelationnfunction. Using a two dimensional (axial and temporal dimension) modelnof the received signal, the bias in velocity and velocity spread isnquantified, both for the autocorrelation algorithm and the time shiftncross-correlation estimator. Theoretical expressions, as well asnnumerical examples are given