Triplet pulse sequence for superior microbubble/tissue contrast

A triplet pulse sequence is proposed for imaging with superior microbubble/tissue selectivity. This sequence utilizes the difference in nonlinearity between the nonlinear propagation in tissue and the nonlinear scattering by microbubbles. Three-time transmit/receive are performed with transmit pulses having the same envelope and a phase shift by 120°, and the received echo signals are summed. Numerical analysis of the microbubble scattering and the propagation in tissue predicted the selectivity superior to the conventional pulse inversion sequence by more than 20 dB in an ideal case. An experiment using a prototype scanner with a Doppler flow phantom and a contrast agent demonstrated an improvement in the selectivity by 15 dB at a typical acoustic amplitude in B-mode imaging at 2 MHz.