A spatially varying pulse compression filter for coded excitation signals

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