A spatially varying pulse compression filter for coded excitation signals

Coded excitation and pulse compression techniques have been used to improve the echo signal-to-noise ratio (eSNR) in ultrasonic imaging. Pulse compression can be performed using a Wiener filter. In this work, the effects of applying a spatially varying Wiener filter were evaluated. Specifically, a technique to adaptively compensate for the spatial changes in eSNR in the compression scheme was examined. Simulations and experiments were conducted with a single-element transducer (f/2.66) having a center frequency of 2.25 MHz and a -3-dB bandwidth of 50%. In simulations, tissue-mimicking phantoms with 12 point targets were imaged. In experiments, anechoic targets from the ATS 539 tissue-mimicking phantom were imaged. For simulated echoes compressed with a spatially varying Wiener filter (SVWF), an increase in eSNR of 235% was obtained over the non-SVWF at depths that typically could not be imaged using a conventional pulsed (CP) excitation. For the experiments with the anechoic targets, it was observed that the contrast-to-noise ratio was improved by 245% over CP when compressing with a SVWF. Simulation and experimental results suggest that accounting for local variations in the eSNR can lead to significant improvements in the compression performance. Specifically, the eSNR was increased in deeper areas imaged at the expense of a small degradation in spatial resolution.