News | Magnetic Resonance Imaging (MRI) | July 13, 2021

Finding prompts researchers, clinicians to consider this impact in future research and clinical treatment of brain diseases

In a mouse model study of MRI-guided focused ultrasound-induced blood-brain barrier (BBB) opening at MRI field strengths ranging from ­approximately 0 T (outside the magnetic field) to 4.7 T, the static magnetic field dampened the detected microbubble cavitation signal and decreased the BBB opening volum

In a mouse model study of MRI-guided focused ultrasound-induced blood-brain barrier (BBB) opening at MRI field strengths ranging from ­approximately 0 T (outside the magnetic field) to 4.7 T, the static magnetic field dampened the detected microbubble cavitation signal and decreased the BBB opening volume. Image courtesy of Washington University in St. Louis


July 13, 2021 — MRI-guided focused ultrasound combined with microbubbles can open the blood-brain barrier (BBB) and allow therapeutic drugs to reach the diseased brain location under the guidance of MRI. It is a promising technique that has been shown safe in patients with various brain diseases, such as Alzheimer's diseases, Parkinson's disease, ALS and glioblastoma. While MRI has been commonly used for treatment guidance and assessment in preclinical research and clinical studies, until now, researchers did not know the impact of the static magnetic field generated by the MRI scanner on the BBB opening size and drug delivery efficiency.

In new research published in Radiology, Hong Chen and her lab at Washington University in St. Louis have found for the first time that the magnetic field of the MRI scanner decreased the BBB opening volume by 3.3-fold to 11.7-fold, depending on the strength of the magnetic field, in a mouse model.

Chen, associate professor of biomedical engineering in the McKelvey School of Engineering and of radiation oncology in the School of Medicine, and her lab conducted the study on 30 mice divided into four groups. After the mice received the injection of the microbubbles, three groups received focused-ultrasound sonication at different strengths of the magnetic field: 1.5 T (teslas), 3 T and 4.7 T, while one group never entered the magnetic field.

They found that the activity of the microbubble cavitation, or the expansion, contraction and collapse of the microbubbles, decreased by 2.1 decibels at 1.5 T; 2.9 decibels at 3 T; and 3 decibels at 4.7 T, compared with those that had received the dose outside of the magnetic field. In addition, the magnetic field decreased the BBB opening volume by 3.3-fold at 1.5 T; 4.4-fold at 3 T; and 11.7-fold at 4.7 T. None of the mice showed any tissue damage from the procedure.

Following focused-ultrasound sonication, the team injected a model drug, Evans blue, to test whether the static magnetic field affects trans-BBB drug delivery efficiency. The images showed that the fluorescence intensity of the Evans blue was lower in mice that received the treatment in one of the three strengths of magnetic fields compared with mice treated outside the magnetic field. The Evans blue trans-BBB delivery was decreased by 1.4-fold at1.5 T, 1.6-fold at 3.0 T and 1.9-fold at 4.7 T when compared with those treated outside of the magnetic field.

"The dampening effect of the magnetic field on the microbubble is likely caused by the loss of bubble kinetic energy due to the Lorentz force acting on the moving charged lipid molecules on the microbubble shell and dipolar water molecules surrounding the microbubbles," said Yaoheng (Mack) Yang, a doctoral student in Chen's lab and the lead author of the study.

"Findings from this study suggest that the impact of the magnetic field needs to be considered in the clinical applications of focused ultrasound in brain drug delivery," Chen said.

In addition to brain drug delivery, cavitation is also the fundamental physical mechanism for several other therapeutic techniques, such as histotripsy, the use of cavitation to mechanically destroy regions of tissue, and sonothrombolysis, a therapy used after acute ischemic stroke. The dampening effect induced by the magnetic field on cavitation is expected to affect the treatment outcomes of other cavitation-mediated techniques when MRI-guided focused-ultrasound systems are used.

For more information: www.wustl.edu


Related Content

News | Magnetic Resonance Imaging (MRI)

April 10, 2024 — Online MRI and CT education leader, ImagingU, announced the launch of a new course for students and ...

Time April 10, 2024
arrow
Feature | Radiation Oncology | By Melinda Taschetta-Millane

In a new 3-part video series on advancements in diagnostic radiology with Robert L. Bard, MD, PC, DABR, FASLMS ...

Time April 10, 2024
arrow
News | Radiation Dose Management

April 9, 2024 — Mirion Dosimetry Services, a Mirion Medical company, today announced commercial availability of its ...

Time April 09, 2024
arrow
News | Ultrasound Imaging

April 9, 2024 — A new Society of Radiologists in Ultrasound (SRU) expert consensus statement to improve endometriosis ...

Time April 09, 2024
arrow
News | Magnetic Resonance Imaging (MRI)

April 8, 2024 — Magnetic resonance-guided focused ultrasound (MRgFUS) is a non-invasive technique for neuroregulation ...

Time April 08, 2024
arrow
News | Magnetic Resonance Imaging (MRI)

April 5, 2024 — Osteoarthritis — not age — may play the greatest role in determining the utility of MRI for patients 45 ...

Time April 05, 2024
arrow
News | Radiology Business

April 4, 2024 — FUJIFILM Healthcare Americas Corporation, a leading provider of diagnostic and enterprise imaging ...

Time April 04, 2024
arrow
Feature | Radiology Business | By Melinda Taschetta-Millane

Here is a snapshot of the Top 10 most-read content from ITN's viewers during the month of March: 1. Philips Teams with ...

Time April 04, 2024
arrow
News | Radiation Oncology

April 2, 2024 — In a 10-center study, microwave ablation offered progression free survival rates and fewer complications ...

Time April 02, 2024
arrow
News | X-Ray

April 1, 2024 — MinXray, a leading manufacturer of imaging systems for medical and veterinary use, recently sent its ...

Time April 01, 2024
arrow
Subscribe Now