Microbubble-mediated focused ultrasound disruption of the blood-brain barrier (BBB) is a promising technique for non-invasive targeted drug delivery in the brain1-3. This protocol outlines the experimental procedure for MRI-guided transcranial BBB disruption in a rat model.
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Method Article
MRI-guided Disruption of the Blood-brain Barrier using Transcranial Focused Ultrasound in a Rat Model
In This Article
Summary
Abstract
Focused ultrasound (FUS) disruption of the blood-brain barrier (BBB) is an increasingly investigated technique for circumventing the BBB1-5. The BBB is a significant obstacle to pharmaceutical treatments of brain disorders as it limits the passage of molecules from the vasculature into the brain tissue to molecules less than approximately 500 Da in size6. FUS induced BBB disruption (BBBD) is temporary and reversible4 and has an advantage over chemical means of inducing BBBD by being highly localized. FUS induced BBBD provides a means for investigating the effects of a wide range of therapeutic agents on the brain, which would not otherwise be deliverable to the tissue in sufficient concentration. While a wide range of ultrasound parameters have proven successful at disrupting the BBB2,5,7, there are several critical steps in the experimental procedure to ensure successful disruption with accurate targeting. This protocol outlines how to achieve MRI-guided FUS induced BBBD in a rat model, with a focus on the critical animal preparation and microbubble handling steps of the experiment.
Protocol
1. Ultrasound and MRI Setup
An MRI-compatible three-axis focused ultrasound system was used in this study (FUS Instruments, Inc., Toronto, Ontario, Canada). Two different ultrasound transducers were used: an in-house constructed 551.5 kHz spherically-focused transducer (radius of curvature = 60 mm, external diameter = 75 mm, internal diameter = 20 mm), and a 1.503 MHz, 8-sector array with integrated PZT hydrophone (Imasonic Inc., Voray-sur-L'Orgnon, France) driven as a single element spherically focused transducer (FN = 0.8, aperture = 10 cm). An MRI-compatible PVDF receiver8 was used to record acoustic emissions when the 551.5 kHz....
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Discussion
Preparation of the animals and microbubbles are the most critical aspects of this procedure. The hair on the animal's head must be entirely removed to avoid attenuating the ultrasound beam. The BBB can be disrupted under isofluorane anesthetic, however, it becomes more difficult to achieve consistent opening.
The microbubbles should always be handled with care and small gauge, large diameter needles must be used when drawing up, in order to avoid breaking them. Similarly, the smallest gauge c.......
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Disclosures
K. Hynynen and R. Chopra are co-founders of FUS Instruments, Inc. R. Chopra, A. Waspe and K. Hynynen are shareholders in FUS Instruments, Inc. K. Hynynen receives research support from FUS instruments, Inc.
Acknowledgements
The authors would like to thank Shawna Rideout-Gros and Alexandra Garces for their help with the animal care, and Ping Wu for her technical assistance. Support for this work was provided by the National Institutes of Health under grant no. EB003268, and the Canada Research Chairs Program.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Small Animal Focused Ultrasound System | FUS Instruments, Inc. | RK-100 | |
| Definity | Lantheus Medical Imaging | ||
| Omniscan | GE Healthcare |
References
- Kinoshita, M., McDannold, N., Jolesz, F. A., Hynynen, K. Noninvasive localized delivery of Herceptin to the mouse brain by MRI-guided focused ultrasound-induced blood-brain barrier disruption. Proc. Natl. Acad. Sci. U.S.A. 103, 11719-11723 (2006).
- Jordão, J. F., Ayala-Grosso, C. A., Markham, K., Huang, Y., Chopra, R., McLaurin, J., Hynynen, K., Aubert, I.
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