Yuexi Huang, Kullervo Hynynen
INTRODUCTION: Drug delivery to the brain is severely limited by the blood-brain barrier (BBB). Focused ultrasound (FUS) combined with intravenously administered microbubbles (MB) offers a promising noninvasive approach for transient and reversible BBB permeability enhancement. AREAS COVERED: Magnetic resonance-guided FUS (MRgFUS) has been well established for thermal ablation, providing precise anatomical targeting and real-time thermometric feedback. Although BBB permeability enhancement does not rely on thermal effects, MRI guidance remains essential. This review highlights the role of MRI in BBB permeability enhancement procedures and summarizes MR sequences used at different stages to optimize targeting accuracy, safety, and therapeutic efficacy. EXPERT OPINION: Because substantial temperature elevation is not expected during BBB permeability enhancement, MR thermometry is not routinely informative in this application. Nevertheless, MRI is central to anatomical and functional targeting for treatment planning and monitoring. Contrast-enhanced T1-weighted imaging enables assessment and localization of BBB permeability enhancement, while T2*-weighted imaging helps identify exposures approaching unsafe levels. Future clinical trials incorporating intraoperative MR guidance are needed to refine and standardize cavitation-based feedback control before developing and adopting systems that do not depend on intraoperative MRI.