Effects of tracking beam dimensions on Harmonic Motion Imaging (HMI) with electronic beam steering of focused ultrasound (FUS)

Abstract

Previous studies from our group have demonstrated successful applications of Harmonic Motion Imaging (HMI) using a single-element focused ultrasound (FUS) transducer and plane wave (PW) imaging. In this paper, a multi-element FUS transducer was used. The effects of tracking beam dimensions on HMI in terms of contrast and CNR were investigated. These new sequences were validated on a tissue-mimicking phantom with embedded cylindrical inclusions, and an in-vivo murine breast tumor model. There were an overall 4.2% and 51.4% increase in contrast and CNR with focused imaging (F/3) compared with the 5-angle plane wave compounding (PWC) sequence for an 8.4-mm inclusion with Young's modulus of 56 kPa within a 5.3-kPa background. Contrast and CNR were not improved as much in the in-vivo murine model with focused imaging; however tumor boundaries were delineated more uniformly with higher transmit focusing. Electronic beam steering of FUS reduced around 4.6-fold data acquisition time without noticeably compromising HMI image quality.