7A-3 Optimal Pulse Sequences for the Suppression of Memoryless Tissue Harmonics

In current methods for contrast-enhanced ultrasound such as phase inversion (PI), the achievable contrast-to-tissue ratio (CTR) is limited by the nonlinear propagation of sound in tissue. A fundamental difference between sound propagation nonlinearity and contrast agent oscillation nonlinearity, however, is the different scale of the nonlinear memory of both effects. To exploit this difference, this paper proposes an optimization approach for the determination of pulses for contrast agent imaging which enhance the signal components originating from contrast agents while suppressing signal components originating from nonlinear sound propagation. For this determination, no exact model of microbubble oscillation and sound propagation is necessary. To validate the obtained pulses for contrast agent imaging, a commercial ultrasound scanner was programmed and imaging on a tissue mimicking phantom was conducted. The proposed sequences allowed for an improvement of the CTR of 14.1 dB in comparison with phase inversion.