Contrast-enhanced MRI of mice treated with focused ultrasound–induced blood-brain barrier (BBB) opening in different magnetic fields. (A) Representative contrast-enhanced T1-weighted horizontal MRI scans show BBB opening in mice sonicated in different magnetic fields (approximately 0, 1.5, 3.0, and 4.7 T; top panel). BBB opening area is superimposed on the T1-weighted MRI scan, with the color indicating the normalized signal intensity (SI) change (bottom panel). (B) Quantification of the BBB opening volume of mice treated in different magnetic fields. (C) Quantification of normalized signal intensity change at the focused ultrasound–targeted location, comparing mice treated in different magnetic fields. Error bars indicate standard error of the mean.