To evaluate the effects of repeated BBB opening by pFUS and microbubbles (MB) on morphology to the rat striatum and hippocampus as monitored by magnetic resonance imaging (MRI), positron emission tomography (PET) and histology over 12 weeks.Female rats were divided into two groups and received either pFUS + MB (Optison^TM, GE Healthcare, Little Chalfont, UK) once or six times targeting the striatum and the contralateral hippocampus. 200 μl of MB were administered intravenously over 1 minute starting 30 sec before pFUS. Rats received 3 daily doses of 300 mg/kg 5-Bromo-2′-deoxy-uridine (BrdU, Sigma Aldrich, St. Louis, MO) intraperitoneally before sonication to label proliferating cells in vivo. 0.3 MPa acoustic pressure was applied in 10 ms burst length and 1% duty cycle (9 focal points, 120 sec/9 focal points – striatum, 120 sec/4 focal points – hippocampus) using a single-element spherical FUS transducer (center frequency: 589.636 kHz; focal number: 0.8; aperture: 7.5 cm; FUS Instruments, Toronto, Ontario, Canada). T2, T2* and Gd-enhanced T1-weighted images were obtained by 3.0 T MRI (Philips, Amsterdam, Netherlands), T2, T2*, diffusion tensor imaging (DTI) and chemical exchange saturation transfer (CEST) imaging was performed by 9.4 T MRI (Bruker, Billerica, MA). Parameters for DTI: 3D spin echo EPI; TR/TE 700 ms/37 ms; b-value 800 s/mm2 with 17 encoding directions; voxel size 200 μm, isotropic. Diffusion weighted images were corrected for B0 susceptibility induced EPI distortion, eddy current distortions, and motion distortion with b-matrix reorientation using Tortoise. Parameter for glucoCEST: 2D fast spin echo with (MT) and without (M0) magnetization transfer (MT) pulses (TR/TE 3.5 s/11.5 ms; in plane resolution: 200 µm, thickness: 0.8 mm; MT pulse: 3 μT, 1 s). The MT offset frequences (Δω) were set from -2 kHz to + 2 kHz with 100 Hz stepping to detect the proton metabolites of glucose (1.2 ppm, 2.1 ppm, 2.9 ppm). Fractional anistropy (DTI-FA) and the asymmetry of magnetization transfer ratio (MTRasym) were derived for mapping structural injury and glucose metabolism. Quantitative of glucose uptake was performed with FDG-PET (Siemens, Munich, Germany). Animals were euthanized 6 or 12 weeks after the first pFUS treatment. Histological evaluation of brain and tracking of BrdU tagged cells was performed at different time points. Values were compared to baseline.Preliminary results showed contrast enhancement on T1-weighted MRI in rats receiving a single sonication, indicating BBB disruption in the striatum and the hippocampus. Gd-extravasation or T2 and T2* abnormalities were not seen in the brain 1 day post-pFUS + MB at 9.4 T MRI. Hypointense regions appeared on T2* MRI 2 weeks post-pFUS + MB (Figure 1, Figure 2) consistent with microhemorrhage within the parenchyma that decreased in volumes by week 3. White matter fiber structure- and gray matter-abnormalities on DTI MRI were detected in regions with the T2* abnormalities (Figure 2) suggestive of astrogliosis. GlucoCEST showed loss of contrast as early as 1 day post-pFUS and it persisted up to week 3.We have observed a complex graded molecular and cellular sterile inflammatory response in the brain up to 24 hrs after pFUS + MB. However, little is known about the long term effects in rats using advanced imaging techniques. The DTI data showed that pFUS caused a low degree of structural injury at the location of sonication. However, the decrease in glucose concentration revealed by glucoCEST indicated that the pFUS could cause hypo-metabolism in the brain, even after three weeks post-sonication. These preliminary results suggest the importance of long term monitor of the brain following low intensity pFUS + MB. Further research investigations are in process to evaluate changes following multiple targeted treatments in the brain.