Mixed Imaging Sequences for Improved Spatiotemporal Resolution in Cardiac Imaging

Ultrasound is a crucial tool for cardiac imaging. Even though modern imaging sequences efficiently manage the trade-off between spatial and temporal resolution, motion in the field-of-view readily degrades image quality. In this work, we seek to design an ultrasound imaging sequence that resolves cardiac motion with fewer total transmissions than conventional sequences, thereby increasing temporal resolution and maintaining spatial resolution. Specifically, we used REFoCUS to combine focused and plane wave transmissions in a “mixed sequence.” First, the motion sensitivity of REFoCUS was evaluated in simulation for a variety of transmit beam geometries. Focused transmissions resolve motion much more effectively than broad transmissions. Second, a mixed sequence was designed that insonifies key targets with focused transmissions and the full field-of-view with plane wave transmissions. This mixed sequence (n=70) was used to image cardiac motion in-vivo and was compared to a focused sequence (n=102) and a plane sequence (n=60). Overall, mixed sequences have strong potential to both resolve cardiac motion and improve imaging frame rate.