Association between contrast-enhanced MR images and blood-brain barrier disruption following transcranial focused ultrasound.

To investigate the correlation between the contrast-enhanced magnetic resonance imaging (MRI) signal and the duration of blood-brain barrier (BBB) disruption induced by focused ultrasound (FUS). FUS was applied to 45 rat brains in the presence of microbubbles, and these rats were scanned on a 3T MRI system at several timepoints. The rat brains were then studied using contrast-enhanced spin echo T1-weighted images. At the same time, BBB disruption was evaluated based on Evans blue (EB) extravasation. The relationship between the normalized signal intensity change of the MRI and EB extravasation was analyzed by least-squares linear regression and the calculation of correlation coefficients. When MRI enhancement was quantitatively evaluated by EB extravasation, a strong correlation between the normalized signal intensity change of the MRI and EB extravasation was identified during BBB disruption after sonication. However, the correlation coefficient decreased as BBB closure occurred after sonication ended. The contrast-enhanced MRI signal can potentially be used to evaluate the amount of chemotherapeutic agents entering the targeted tissue, but the accuracy of the assessment will be affected by the time interval since sonication.