Monitoring of acoustic cavitation in microbubble‐presented focused ultrasound exposure using gradient‐echo MRI

Background Gadolinium‐based contrast agents can be used to identify the blood–brain barrier (BBB) opening after inducing a focused ultrasound (FUS) cavitation effect in the presence of microbubbles. However, the use of gadolinium may be limited for frequent routine monitoring of the BBB opening in clinical applications. Purpose To use a gradient‐echo sequence without contrast agent administration for monitoring of acoustic cavitation. Study Type Animal and phantom prospective. Phantom/Animal Model Static and flowing gel phantoms; six normal adult male Sprague–Dawley rats. Field Strength/Sequence 3T, 7T; fast low‐angle shot sequence. Assessment Burst FUS with acoustic pressures = 1.5, 2.2, 2.8 MPa; pulse repetition frequencies = 1, 10,100 Hz; and duty cycles = 2%, 5%, 10% were transmitted to the chamber of a static phantom with microbubble concentrations = 10%, 1%, 0.1%. MR slice thicknesses = 3, 6, 8 mm were acquired. In flowing phantom experiments, 0.1%, 0.25%, 0.5%, 0.75%, and 1% microbubbles were infused and transmitted by burst FUS with an acoustic pressure = 0.4 and 1 MPa. In in vivo experiments, 0.25% microbubbles was infused and 0.8 MPa burst FUS was transmitted to targeted brain tissue beneath the superior sagittal sinus. The mean signal intensity (SI) was normalized using the mean SI from pre‐FUS. Statistical Tests Two‐tailed Student's t‐test. P