Preclinical/clinical scientist interested in using high resolution MRI and DTI for in vivo assessment of neurological diseases in genetic animal models of early hypoxic/ischemic neonatal injury. The clinical consequence of white matter (WM) injury within the developing brain, as often occurs when babies are born preterm and at low birth weight, is cerebral palsy. This disease is characterized by a lifelong abnormality of motor control that results in spasticity, making activities of daily living like feeding oneself or walking difficult.¹ At present, there are no proven preventative therapies. In vivo assessment of experimental interventions are required to facilitate the progression of preclinical studies to clinical relevance. Previously, we found that microRNA-21 (miR-21) increased robustly following injury using the Vannucci model of global hypoxic-ischemic (HI) neonatal brain injury. Given that overexpressed miR-21 following HI plays a major role in WM injury formation we downregulated miR-21 by conditionally and inducibly expressing a miR-21 “sponge” construct in NG2 cells, using an NG2CreERT2 stop floxed; MSP mutant mouse. DTI has been shown to provide a good measure in models of brain injury In this study we used a multi-direction (64 directions), multi b-value (0, 300, 900, 1800 mm/sec²) DTI acquisition scheme to generate relevant MR parameters for assessment of long term WM injury and neuronal reorganization in this genetic mouse model.NG2CreERT2;MSP mice underwent HI or sham surgery and treated with tamoxifen (60mg/kg IP) or vehicle daily for 4 days post-injury. MRI occurred two months after injury. Four groups were scanned: sham/vehicle (n=4), sham/tamoxifen (n=4), HI/vehicle (n=4), and HI/tamoxifen (n=6). All MRI was done on 7T Bruker Clinscan (Syngo MRI). A multi direction (64 directions) and multiple b-value (0, 900 and 1800 mm/sec²) EPI-Sequence was used with the following geometrical and MR parameters (294um in plane and 0.8mm slice thickness, TR = 5sec, TE = 28msec, for a total acquisition time ~ 43 minutes). High resolution 3D isotropic (100um) was also obtained for each animal for morphometric analysis. DTI parameters were generated using DSI Studio and data extracted from manually drawn regions of interest (ROI) in commissure (AC), cerebral peduncle (CP), fimbria of hippocampus (FH), genu (GU), and internal capsule (IC). The median FA of each ROI was selected to represent the region. A two tailed t-test was performed for each region comparing vehicle and tamoxifen, and for left lateral ventricle to right lateral ventricle ratio comparing sham and HI. Diffusion tensor tractography (DT) was also performed using a FA threshold of 0.2.Sham/tamoxifen exhibits higher FA in areas near the ventricle, FH, GU, and IC, while exhibiting decreased FA in CP and AC compared to sham/vehicle (Fig.1a). HI/tamoxifen consistently exhibits decreased FA in CP, FH, IC, and exhibits a significant decrease in AC (p<0.05) compared to HI/vehicle (Fig.1b). Tamoxifen effects on GU are less pronounced in both sham and HI group. No statistical differences between sham/vehicle and HI/vehicle (Fig.1a,b) was seen. Representative DT is shown for AC in both HI/vehicle (Fig.1c) and HI/tamoxifen (Fig.1d). Significant lateral ventriculomegaly (p<0.0057) and decreased hippocampus volume was observed and measured ipsilaterally to lesion but no significant changes were observed contralaterally in HI/Vehicle versus sham/vehicle.The general decrease in FA across HI/tamoxifen provides evidence for WM injury, most prominently exhibited in AC. Tractography suggests prominent loss of WM tracts towards the occipital lobe in HI/tamoxifen cohort. Due to small size of FH and IC ipsilateral to lesion, ROIs could not be drawn for HI cohorts. Thus, only indirect, contralateral effects in FH and IC are observed in Figure 1a and b, explaining why there are no statistical differences between sham/vehicle and HI/vehicle. Similar results are reported in an ex vivo study, confirming our in vivo findings.² However our results suggests that more details are needed to interpret the data. Histopathology is being conducted to further interpret imaging data. The specific results in this work suggest that Tamoxifen does not have a significant effect on sham/tamoxifen, but exhibits significant neurotoxic effects in HI/tamoxifen, especially in the AC region. Quantitative non-invasive MRI and DTI using multiple diffusion directions and multiple b-values provide essential tools to investigate underlying processes associated with neurological progression to cerebral palsy using genetic models and HI induced injury.