Improving signal-to-noise ratio through generalized multipulse transmit encoding

Diagnostic imaging of deep targets in the body requires sufficient signal amplitude to overcome effects such as attenuation with depth and thermal noise produced in signal reception. Coded excitation provides several strategies to increase the total transmitted energy without exceeding peak amplitude safety limits. Temporal coding has proven particularly effective, but these frequency or amplitude modulation techniques require additional transmit capabilities and often require complex processing to reduce decoding artifacts. We present an alternative code based on time delays that relies on identical transmit pulses that can be decoded using spatiotemporal synthetic aperture processing. We experimentally demonstrate a 16-pulse code that achieves an 11.1 dB improvement in signal-to-noise ratio (SNR) while maintaining axial resolution and sufficient range lobe performance. We compare our technique to Barker code and observe trade-offs in the resulting point spread function with only a slightly lower gain in SNR.