MRI-guided focused ultrasound was tested in the brains of rhesus monkeys. Locations up to 4.8 cm deep were targeted. Focal heating was observed in all cases with MRI-derived temperature imaging. Subthreshold heating was observed at the focus when the ultrasound beam was targeted with low power sonications, and in the ultrasound beam path during high-power exposures. Lethal temperature values and histologically confirmed tissue damage were confined to the focal zone (e.g., not in the ultrasound beam path), except when the focus was close to the bone. In that case, damage to the neighboring brain tissue was observed. Focal lesions were observed on histological examination and, in some cases, in MR images acquired immediately after the ultrasound exposures. The capabilities demonstrated in this study will be of benefit for clinical ultrasound therapies in the brain.
Copyright 2003 Wiley-Liss, Inc.