Precise Manipulation of Bubble Cavitation and Blood-Brain Barrier Modulation using Temporal Interference Ultrasound.

Objective: To determine whether temporal interference (TI) ultrasound can enhance microbubble (MB) cavitation and provide transient modulation of blood-brain barrier (BBB) permeability. Impact Statement: By integrating a time-dependent multiphysics MB-vessel model with in vivo validation, this study links TI-enhanced cavitation dynamics to vessel-wall mechanical responses and a transient BBB permeability window, providing a mechanistic basis for pressure-efficient ultrasound-mediated brain delivery. Introduction: Focused ultrasound combined with MBs can transiently increase BBB permeability, but reliable control of cavitation intensity and post-sonication barrier recovery remains a key challenge for safe and effective brain delivery. Methods: A fluid-solid coupled MB-vessel model was used to evaluate MB dynamics, vessel-wall normal and shear stresses, porosity, acoustic-pressure dependence, and the influence of non-Newtonian blood rheology under 1.0 MHz single-frequency and 1.0 + 0.8 MHz TI excitation. In vivo Evans blue experiments in mice were then used to compare BBB opening across pressure levels and to characterize the recovery profile from 0.5 to 12 h after 0.3-MPa TI sonication. Results: Ultrasound-driven MB oscillation and collapse increased vessel-wall stress and modeled porosity. Compared with single-frequency ultrasound, TI excitation promoted earlier MB instability and collapse and produced stronger vessel-wall mechanical responses under energy-equivalent acoustic exposure conditions. In vivo, Evans blue extravasation increased with the reference pressure amplitude and showed higher mean values following TI ultrasound, with a significant between-mode difference at 0.5 MPa. After 0.3-MPa TI sonication, extravasation progressively decreased from 0.5 to 12 h, consistent with a transient BBB permeability increase. Non-Newtonian rheology altered the local shear environment but had limited effects on peak normal stress and porosity within the simulated time window. Conclusion: TI ultrasound enhances MB-mediated BBB opening under energy-normalized acoustic exposure conditions while producing a time-limited increase in permeability, supporting its further development for temporally controlled brain delivery.