Focused ultrasound blood-brain barrier opening: a review of post-procedure MRI outcomes

INTRODUCTION: Focused ultrasound (FUS) blood-brain barrier opening (BBBo) is an incisionless technique that facilitates cerebral drug delivery by temporarily increasing BBB permeability. Clinical trials have shown that FUS produces reversible BBBo and is feasible in humans. There are currently no standardized imaging protocols for assessing the safety of FUS-BBBo, although MRI is commonly performed. AREAS COVERED: This structured narrative review summarizes neuroimaging techniques used to assess FUS-BBBo safety in clinical trials of participants with neurological disorders that reported post-procedural MRI findings. A search of PubMed from September 2014 to April 2026 was undertaken to identify clinical trials of FUS-BBBo (13 in patients with brain tumors and 16 in neurodegenerative diseases). EXPERT OPINION: Localized T2* hypointense signals and T2 hyperintense signals are relatively common after FUS-BBBo. While these findings have been thought to be related to transient microhemorrhage or edema, no consistent association has been found between such findings and clinically significant adverse events. Further work incorporating standardized post-FUS-BBBo MRI safety assessments is needed to clarify the biological significance of these signal alterations, and to determine whether they indicate a potential long-term safety concern, are a harmless finding associated with the BBBo procedure, or are associated with the underlying diseases and/or concomitant drugs.