PROJECT ABSTRACT Spinal cord injuries (SCI) initiate a cascade of complex physiological and molecular mechanisms at and around the site of injury. Beyond the initial damage, secondary and chronic neuropathological effects triggered by neuroinflammation and molecular changes at the injury site can severely impact spinal cord regeneration. Some of the mechanisms of interest include glutamate excitotoxicity, demyelination, glial scar formation, toxic free radical accumulation, and pro-inflammatory cytokine release. These secondary and chronic pathological effects can severely impede spinal cord regeneration through inhibition of axonal regrowth and progressive cell death at the injury site. Multi-parametric MRI (mpMRI) provides an array of contrasts sensitive to changes that occur in SCI. Quantitative magnetization transfer (qMT) imaging characterizes myelin concentration changes through measurements of immobile macromolecular content. Diffusion tensor imaging (DTI) provides complementary structural information by evaluating spinal cord axonal tract integrity post-injury. Resting-state functional MRI (rsfMRI) reports the integrity of gray matter resting state functional networks that are disrupted post-injury. Chemical exchange saturation transfer (CEST) and Nuclear Overhauser Enhancement (NOE) imaging generates Z-spectra that reflect changes in the concentrations and/or exchange rates of specific metabolites and macromolecules, providing high resolution molecular information from the SCI region. In addition, PET imaging using radiotracers that bind specifically to the translocator protein (TSPO) will provide three-dimensional spatial maps of neuroinflammatory activity in the injured spine and can validate the interpretation of mpMRI measures. We hypothesize that using mpMRI, we can detect and quantify relevant structural, functional, and molecular changes in the spinal cord, longitudinally over time, in a rat injury model, and that imaging metrics can be used as biomarkers of the effects of therapeutic interventions. These biomarkers will correlate with animal functional recovery and can be used to evaluate the efficacy of SCI treatments. We will evaluate the validity of these hypotheses in the proposed study. First, we will optimize and implement CEST and NOE MR sequence protocols for imaging SCI rats. Next, we will combine mpMRI imaging modalities to measure the sensitivity of mpMRI for quantifying SCI severity and recovery and for evaluating the efficacy of SCI treatments, in a treatment study using the neuroprotective drug Riluzole. Finally, we will confirm the structural, molecular, and behavioral basis of the mpMRI imaging metrics through TSPO PET imaging of neuroinflammation, motor and somatosensory behavior testing, and histological analysis. The proposed studies are significant because they will develop, validate, and implement innovative mpMRI methods that can evaluate and track various neuropathological changes that accompany recovery af...