Static magnetic fields dampen focused ultrasound-induced cavitation and blood-brain barrier opening outcome

Abstract

MRI-guided focused ultrasound combined with microbubbles has been used in clinical studies for blood-brain barrier (BBB) opening. However, the impact of the static magnetic field generated by an MRI scanner on the BBB opening outcome has not been evaluated. The objective of this study was to determine the relationship of the static magnetic field of an MRI scanner on focused ultrasound combined with microbubble-induced BBB opening. Mice were divided into four groups which were sonicated by FUS in different static magnetic fields B0 (∼0T, 1.5T, 3.0T, and 4.7T) with all other experimental parameters kept the same. Microbubble cavitation activity was monitored by passive cavitation detection during FUS after microbubble injection. After sonication, contrast-enhanced T1-weighted MRI and Evans blue were used to evaluate the BBBO outcome. The microbubble cavitation dose decreased by an average of 2.1 dB at 1.5T (P = 0.05), 2.9 dB at 3.0T (Pi = 0.01), and 3.0 dB at 4.7T (P = 0.01) compared with that outside the magnetic field. It also decreased Evans blue trans-BBB delivery 1.4-fold at1.5T (P = 0.009), 1.6-fold at 3.0T (P < 0.001), and 1.9-fold at 4.7T (P < 0.001). These findings demonstrated that static magnetic fields dampened microbubble cavitation and decreased trans-BBB delivery by FUS.