Feedback control of microbubble cavitation for ultrasound

Focused ultrasound (FUS) in combination with microbubbles is capable of noninvasive, site-targeted delivery of drugs through the blood–brain barrier (BBB). Although acoustic parameters are reproducible in small animals, their control remains challenging in primates due to skull heterogeneity. This study describes a 7-T magnetic resonance (MR)-guided FUS system designed for BBB disruption in non-human primates (NHP) with a robust feedback control based on passive cavitation detection (PCD). Contrast enhanced T1-weighted MR images confirmed the BBB opening in NHP sonicated during 2？min with 500-kHz frequency, pulse length of 10？ms, and pulse repetition frequency of 5？Hz. The safe acoustic pressure range from 185？±？22？kPa to 266？±？4？kPa in one representative case was estimated from combining data from the acoustic beam profile with the BBB opening and hemorrhage profiles obtained from MR images. A maximum amount of MR contrast agent at focus was observed at 30？min after sonication with a relative contrast enhancement of 67%？±？15% (in comparison to that found in muscles). The feedback control based on PCD using relative spectra was shown to be robust, allowing comparisons across animals and experimental sessions. Finally, we also demonstrated that PCD can test acoustic coupling conditions, which improves the efficacy and safety of ultrasound transmission into the brain