Compared with the acoustic responses in tissues, microbubbles (MBs) present the stronger nonlinear scattering under insonation, which can contribute to distinguishing the perfused regions from the surrounding tissues and further to characterizing the microvascular hemodynamic features. However, the MB nonlinear scattering was additionally influenced by the dual-frequency guided waves generated from the bone cortex and the hemodynamic features enhanced by MBs were inevitably underestimated in the nonuniform acoustic field. Thus, the interaction between the guide waves and MBs was first investigated and pulse inversion technique was used to balance the enhancement of contrast and degeneration of resolution in MB backscattered echoes induced by the guided waves. The concentration of MBs was then successfully characterized by using the statistical Nakagami parameter to recover the hemodynamic underestimations marked by MBs in the nonuniform acoustic field. Tissue distortion caused by breathing motion was overcome by using respiratory gating scheme to guarantee the hemodynamic quantification. Finally, the transient hemodynamic distributions of perfusion volume, blood flow, and flow rate were well characterized, which may provide accurate diagnoses and appropriate therapeutic strategies for tumors.
Diya Wang was born in Gansu, China, in 1985. He received the Ph.D. degrees in Biomedical Engineering from Xi’an Jiaotong University, Shaanxi, China, in 2016. Currently, he is working as a postdoctoral researcher in the laboratory of biorheology and medical ultrasonics at the University of Montreal, Canada. His research focuses on biomedical ultrasound imaging and instruments, machine learning in ultrasound imaging.