Pulse inversion sequences for mechanically scanned transducers.

Mechanically scanned transducers are currently used for tissue harmonic imaging (THI) and nonlinear microbubble imaging at high frequencies. The pulse inversion (PI) technique is widely used for suppressing the fundamental signal, but its effectiveness is reduced by relative tissue/transducer motion. In this paper, we investigate multipulse inversion (MPI) sequences that achieve a significant improvement on the fundamental suppression for mechanically scanned single-element transducers. MPI was subsequently applied on simulated and measured RF-data and relative fundamental suppression was compared with the 2-pulse PI technique. Simulations showed, for example, an increased fundamental suppression of 6 and 10 dB for MPI-sequences that combined 3 and 7 pulses, respectively, for a rotating intravascular ultrasound transducer with an interpulse angle of 0.15 degrees. Initial application of MPI sequences on RF-data from in vivo acquisitions resulted in similar fundamental suppression levels. The investigated MPI technique will help to reduce relative tissue/transducer motion effects and might lead to improved sensitivity and spatial resolution in nonlinear tissue imaging and improved microbubble detection in contrast imaging for mechanically scanned transducers.