Following the FUS procedure, the mouse was transferred to the Bruker BioSpec 94/20 scanner (field strength, 9.4 T; bore size, 30 cm) horizontal small animal MRI scanner with software ParaVision 6.0.1 (Bruker BioSpin, Billerica, MA, USA), an 86-mm inner diameter birdcage 1H volume transmits coil and a 1H mouse-head-only Cryogenic RF coil (CryoProbeTM). Mice were anesthetized using medical air and isoflurane (3% volume for induction, 1.1–1.5% for maintenance at 1 liter/min airflow, via a nose cone). The DCE-MRI images were acquired using a 2-D FLASH T1-weighted sequence (180 × 150 × 18 × 84 matrix size, spatial resolution of 100 × 100 μm2, slice thickness of 500 μm, TR/TE = 200/2.12 ms) before (i.e., the first four scans) and during the intraperitoneal (IP) injections of the contrast agent Gadodiamide (Gd) (Omniscan; GE Healthcare, Princeton, NJ, USA).
A contrast agent was used as a tracer to depict the area of the BBB-opening. We injected the contrast agent at two time points to obtain MRI scans with different volumes of contrast agent. We first injected 10 mmol/kg GBCAs, which is 3.3% of the full dosage of the GBCAs (low dose), then administered the remaining 97.7% GBCAs (full dose). For each of the injections, we acquired four-dimensional DCE T1-weighted anatomical brain MRI images with 18 slices and 48 acquisitions respectively. The total acquisition time for DCE-MRI was approximately 1 hour. The timeline for FUS and DCE-MRI image acquisition is shown in Fig. 1(a). Schematic showing the timeline for MRI image acquisition and image processing pipeline.