Complementary-Aperture Pulse Sequencing for Fundamental-Band Nonlinearity Parameter Imaging

Abstract

The depletion method (DM) enables the estimation of the acoustic nonlinearity parameter, B/A, in pulse-echo ultrasound using fundamental-band signals from low- and high-pressure acquisitions, but requires accurate knowledge of the acoustic-pressure scaling factor. This requirement limits experimental translation because of the slightly nonlinear scaling between excitation voltage set on the ultrasound system and pressure at the probe. We propose a complementary-aperture pulse sequence (CAPS) that recovers the linearly scaled low-pressure signal by coherently summing RF acquisitions from interleaved transmit subapertures whereas a full-aperture transmission provides the high-pressure signal maintaining the same excitation voltage configured in the ultrasound system. In silico phantoms of a homogeneous sample and a reference evaluated four aperture partitions of CAPS and compared them with the DM under relative scaling-factor errors from 0.01% to 10%. Using the DM, errors of 0.1% and 1% produced absolute B/A biases of up to 27.3% and 58.3%, respectively. CAPS yielded mean B/A values of 8.9 for a prescribed value of 9, with biases of less than 1.3% across all partitions, matching an ideally calibrated DM. These results demonstrate that CAPS preserves depletion-based B/A estimation without using the pressure scaling factor as a reconstruction input, supporting experimental and in vivo implementation without pressure-ratio calibration.