and Compensation of Ultrasonic Distortion Using a Blind System
Feng Han Lin, Robert C. Waag · 2002
A common random input filter model is de- scribed for estimation and correction of wavefront aberra- tion in ultrasonic b-scan imaging. In the model, aberration between the focus and the transducer elements is repre- sented by the response of a linear filter bank to a com- mon random signal. The response of each filter in the bank is found using a two-level extension of an existing sub- space method for blind system identification. The receive waveforms are compensated using an inverse filter, and the transmit waveforms are predistorted using time reversal. To test the model, experiments were conducted using a two- dimensional array system to obtain echoes from a point re- flector and from a random medium in each case through an aberrator. The aberrator is a phantom that mimics wave- front distortion produced by human abdominal wall, and the random medium is made to mimic ultrasonic charac- teristics of human liver. The results indicate the method can improve both the transmit and the receive focus and can outperform time-shift estimation and compensation as well as the method of backpropagation followed by time- shift estimation and compensation.