Improving sensitivity in acoustoelectric imaging with coded excitation and optimized inverse filter

Acoustoelectric imaging (AEI) is based on the interaction between a pressure wave and tissue resistivity to map electrical current at high spatial resolution. This approach overcomes limitations with conventional bioelectrical imaging, which typically suffers from poor resolution due to the ambiguous conductivity distribution between the current sources and detection electrodes. As we have shown in a variety of preparations, including the live rabbit heart, the magnitude of the AE signal at physiological current is weak (~1 μV). In this study, we examine the role of the pulse waveform in amplifying the AE signal and improving the signal-to-noise ratio for imaging. Using both simulation and bench-top experiment with a standard broadband ultrasound transducer, we analyze the effects of nonlinear coded excitation with optimized compression. Compared to a short linear frequency modulated pulse (chirp), the nonlinear chirp with optimized inverse filtering can improve the signal to noise ratio (SNR) under certain conditions by >6 dB while preserving high spatial resolution.