Image-Guided Focused-Ultrasound CNS Molecular Delivery: An Implementation via Dynamic Contrast-Enhanced Magnetic-Resonance Imaging.

Focused ultrasound (FUS) exposure with microbubbles can transiently open the blood-brain barrier (BBB) to deliver therapeutic molecules into CNS tissues. However, delivered molecular distribution/concentration at the target need to be controlled. Dynamic Contrast-Enhanced Magnetic-Resonance Imaging (DCE-MRI) is a well-established protocol for monitoring the pharmacokinetic/pharmacodynamic behavior of FUS-BBB opening. This study investigates the feasibility of using DCE-MRI to estimate molecular CNS penetration under various exposure conditions and molecule sizes. In the 1 ^st stage, a relationship among the imaging index K _trans , exposure level and molecular size was calibrated and established. In the 2 ^nd stage, various exposure levels and distinct molecules were applied to evaluate the estimated molecular concentration discrepancy with the quantified ones. High correlation (r ²  = 0.9684) between K _trans and transcranial mechanical index (MI) implies K _trans can serve as an in vivo imaging index to mirror FUS-BBB opening scale. When testing various molecules with the size ranging 1-149 kDa, an overall correlation of r ²  = 0.9915 between quantified and predicted concentrations was reached, suggesting the established model can provide reasonably accurate estimation. Our work demonstrates the feasibility of estimating molecular penetration through FUS-BBB opening via DCE-MRI and may facilitate development of FUS-induced BBB opening in brain drug delivery.