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Updated: Oct 29, 2025
MRI-guided Disruption of the Blood-brain Barrier using Transcranial Focused Ultrasound in a Rat Model
Published on: March 13, 2012
Static Magnetic Fields Dampen Focused Ultrasound-mediated Blood-Brain Barrier Opening
Yaoheng Yang1, Christopher Pham Pacia1, Dezhuang Ye1
1From the Departments of Biomedical Engineering (Y. Yang, C.P.P., D.Y., Y. Yue, C.Y.C., H.C.) and Radiation Oncology (H.C.), Washington University in St Louis, 4511 Forest Park Ave, St Louis, MO 63108.
Abstract:
Background Focused ultrasound combined with microbubbles has been used in clinical studies for blood-brain barrier (BBB) opening in conjunction with MRI. However, the impact of the static magnetic field generated by an MRI scanner on the BBB opening outcome has not been evaluated. Purpose To determine the relationship of the static magnetic field of an MRI scanner on focused ultrasound combined with microbubble-induced BBB opening. Materials and Methods Thirty wild-type mice were divided into four groups. Mice from different groups were sonicated with focused ultrasound in different static magnetic fields (approximately 0, 1.5, 3.0, and 4.7 T), with all other experimental parameters kept the same. Focused ultrasound sonication was performed after intravenous injection of microbubbles. Microbubble cavitation activity, the fundamental -physical mechanism underlying focused ultrasound BBB opening, was monitored with passive cavitation detection. After sonication, contrast-enhanced T1-weighted MRI was performed to assess BBB opening outcome. Intravenously injected Evans blue was used as a model agent to evaluate trans-BBB delivery efficiency. Results The microbubble cavitation dose decreased by an average of 2.1 dB at 1.5 T (P = .05), 2.9 dB at 3.0 T (P = .01), and 3.0 dB at 4.7 T (P = .01) compared with that outside the magnetic field (approximately 0 T). The static magnetic field of an MRI scanner decreased BBB opening volume in mice by 3.2-fold at 1.5 T (P < .001), 4.5-fold at 3.0 T (P < .001), and 11.6-fold at 4.7 T (P <.001) compared with mice treated outside the magnetic field. It also decreased Evans blue trans-BBB delivery 1.4-fold at 1.5 T (P = .009), 1.6-fold at 3.0 T (P < .001), and 1.9-fold at 4.7 T (P < .001). Conclusion Static magnetic fields dampened microbubble cavitation activity and decreased trans-blood-brain barrier (BBB) delivery by focused ultrasound combined with microbubble-induced BBB opening. © RSNA, 2021 An earlier incorrect version of this article appeared online. This article was corrected on July 8, 2021.
Insights
Static magnetic fields from MRI scanners significantly reduce the effectiveness of focused ultrasound and microbubbles for opening the blood-brain barrier (BBB). This study demonstrates that stronger magnetic fields lead to diminished microbubble cavitation and reduced drug delivery across the BBB.
Area of Science:
- Neuroscience
- Biomedical Engineering
- Radiology
Background:
- Focused ultrasound (FUS) combined with microbubbles is a clinical method for blood-brain barrier (BBB) opening during MRI.
- The influence of MRI's static magnetic field on FUS-induced BBB opening efficacy remains uninvestigated.
Purpose of the Study:
- To evaluate the relationship between MRI static magnetic field strength and FUS-mediated BBB opening.
- To determine the impact of static magnetic fields on microbubble cavitation and trans-BBB delivery.
Main Methods:
- Thirty wild-type mice were divided into four groups and sonicated with FUS under varying static magnetic fields (0, 1.5, 3.0, 4.7 T).
- Microbubble cavitation activity was monitored using passive cavitation detection.
- BBB opening was assessed via contrast-enhanced T1-weighted MRI, and trans-BBB delivery was evaluated using Evans blue.
Main Results:
- Microbubble cavitation dose decreased significantly with increasing magnetic field strength (2.1 dB at 1.5 T, 2.9 dB at 3.0 T, 3.0 dB at 4.7 T).
- BBB opening volume was reduced by 3.2-fold at 1.5 T, 4.5-fold at 3.0 T, and 11.6-fold at 4.7 T compared to the 0 T group.
- Evans blue delivery across the BBB was reduced by 1.4-fold at 1.5 T, 1.6-fold at 3.0 T, and 1.9-fold at 4.7 T.
Conclusions:
- Static magnetic fields from MRI scanners demonstrably dampen microbubble cavitation activity.
- The presence of static magnetic fields significantly reduces the efficacy of FUS and microbubbles for trans-BBB delivery.
- These findings highlight a critical interaction affecting FUS-based therapeutic delivery strategies.
