Noninvasive MR imaging-guided focal opening of the blood-brain barrier in rabbits

PURPOSE: To determine if focused ultrasound beams can be used to locally op en the blood-brain barrier without damage to surrounding brain tissue and i f magnetic resonance (MR) imaging can be used to monitor this procedure. MATERIALS AND METHODS: The brains of 18 rabbits were sonicated (pulsed soni cation) in four to six locations, with temporal peak acoustic power ranging from 0.2 to 11.5 W. Prior to each sonication, a bolus of ultrasonographic (US) contrast agent was injected into the ear vein of the rabbit. A series of fast or spoiled gradient-echo MR images were obtained during the sonicat ions to monitor the temperature elevation and potential tissue changes. Con trast material-enhanced MR images obtained minutes after sonications and re peated 1-48 hours later were used to depict blood-brain barrier opening. Wh ole brain histologic evaluation was performed. RESULTS: Opening of the blood-brain barrier was confirmed with detection of MR imaging contrast agent at the targeted locations. The lowest power leve ls used produced blood-brain barrier opening without damage to the surround ing neurons. Contrast enhancement correlated with the focal signal intensit y changes in the magnitude fast spoiled gradient-echo MR images. CONCLUSION: The blood-brain barrier can be consistently opened with focused ultrasound exposures in the presence of a US contrast agent. MR imaging si gnal intensity changes may be useful in the detection of blood-brain barrie r opening during sonication.