Canines and humans share many neurobiological and cognitive features of aging. With age, dogs naturally develop a classic pathological hallmark of Alzheimer’s disease (AD), the aggregation of senile beta-amyloid (Aβ) plaques. The burden of Aβ in the dog brain correlates with worsening cognitive symptoms similar to patients early along the AD continuum with mild cognitive impairment (MCI). A large body of work has characterized such features from behavioral experiments followed by postmortem neurobiological evaluations of AD-related pathology in aging beagles. However, far less is known about the dynamics of canine structural brain aging in vivo. Identifying where in vivo biomarkers of aging in the canine recapitulates those of human aging would thus offer a tremendous advantage for translating preclinical treatment outcomes to effective therapeutics for AD. The goal of the work in this dissertation was to discover translational structural neuroimaging biomarkers of aging that could be used to differentiate typical aging from treatment-related effects in the aging canine. We designed a longitudinal neuroimaging analysis pipeline for a multi-year preclinical study in middle-aged beagles evaluating the impact of long-term behavioral enrichment combined with tacrolimus, an FDA-approved calcineurin inhibitor, or Q134R, an experimental small chemical compound with inhibitory properties on the nuclear factor of activated T-cells (NFAT), a substrate of calcineurin. Using complementary volumetry approaches from longitudinal T1-weighted imaging, we find important replications of differential atrophy patterns across the brain including rapid frontal lobe atrophy previously observed in aging beagles. Further, we observed early volume changes common to human aging and early AD not previously described in the canine such as focal posterior cingulate cortical atrophy. We observed a slowing of subcortical atrophy and distinct increases to hippocampal volume across all treatment groups, potentially revealing the beneficial effects of long-term behavioral enrichment. Extending this analytical framework to multi-shell diffusion-weighted imaging (DWI), we observed changes over time to gray matter microstructure consistent with human aging that were selectively mitigated within the hippocampus of tacrolimus-treated dogs, demonstrating the efficacy of chronic calcineurin inhibition on protecting hippocampal microstructure against aging effects. Examinations of whole-brain white matter diffusion changes revealed an anterior-posterior gradient of microstructural changes across all groups that were distinctly reversed within the genu of the corpus callosum, a potential benefit of longitudinal behavioral enrichment to white matter integrity. These findings provide important evidence of longitudinal in vivo structural alterations that are highly similar to human aging and demonstrate that these biomarkers can be leveraged to reliably distinguish typical aging from intervention effects. Evaluations of these cross-species structural biomarkers in future preclinical investigations of AD therapeutics using the canine model can greatly enhance the translation of treatment effects to human clinical trials.