Acoustic pressure configuration of dual-frequency composite acoustic-vortex fields for efficient ultrasound thrombolysis in blood-flow environments

Extracorporeal ultrasound thrombolysis holds great application potential due to its merits of non-invasiveness, precise targeting, and short treatment duration. A dual-frequency composite acoustic-vortex (AV) field, composed of coaxial confocal focused ultrasound (FU) and focused acoustic vortex (FAV) beams generated by a focused transducer array, was utilized to markedly improve thrombolysis efficiency through the synergistic effects of acoustic trapping force, shear stress, acoustic streaming, and acoustic cavitation. However, the accurate trapping-center shift of thrombus fragments induced by the composite pressure pattern and blood flow, as well as the dominant beat-frequency pressure fluctuations in governing cavitation activity and thrombolysis efficiency, have been neglected in existing analyses. In this study, an acoustic pressure configuration strategy for dual-frequency composite fields was proposed to achieve efficient ultrasound thrombolysis in blood-flow environments. The distributions of acoustic pressure and acoustic gradient force within the focal plane were investigated based on the pressure maps of FU and FAV. Considering the blood-flow induced drag force, the pressure pattern influences of FU and FAV on the shift of zero-resultant-force trapping centers for thrombus fragments and microbubbles were analyzed, thereby identifying the pressure range enabling stable capture inside the vortex region. Furthermore, a cavitation intensity evaluation algorithm for beat-frequency fluctuations at the shifted trapping center was developed, based on the time integral of the squared pressure exceeding the cavitation threshold. Finally, optimal pressure ranges of FU and FAV beams within safe pressure limits were determined to achieve both stable trapping and effective cavitation for efficient ultrasound thrombolysis. The favorable results provide theoretical bases and technical support for acoustic pressure regulation in high-efficiency ultrasound thrombolysis using a dual-frequency composite acoustic field generated by a transducer array.