Normative trajectories of R ₁ , R ₂ *, and magnetic susceptibility in basal ganglia on healthy ageing

Quantitative MRI (qMRI) techniques, including R₁, R₂*, and magnetic susceptibility mapping, have emerged as promising tools for generating surrogate imaging markers of brain tissue microstructure, enabling non-invasive in vivo measurements associated with myelination and iron deposition. Gaining insights into how these quantitative measurements evolve throughout a normal lifespan can enhance our understanding of brain maturation processes and facilitate studies of disease-related microstructural changes by distinguishing pathological alterations from normal brain development. In this study, we established the normative trajectories of R₁, R₂*, and magnetic susceptibility in the basal ganglia at 3T. We used a healthy ageing cohort comprising 260 subjects with an evenly distributed age range (from 18 to 80 years) and sex ratio throughout adulthood. Utilising the non-parametric Gaussian Process Regression model to derive the normative trajectories, we found that R₁in these structures predominantly exhibits a quadratic shape over age, while R₂* and magnetic susceptibility are primarily linear. We validated the normative trajectories of R₂* and magnetic susceptibility using an independent cohort. This result reinforces existing findings on the association between age and qMRI. Additionally, we demonstrated that the spatial distributions of the qMRI parameters also change with age in the putamen and caudate nucleus. Finally, the utility of normative modelling of qMRI in the basal ganglia is validated using an independent cohort comprising both healthy participants and individuals with Parkinson's disease, with comparable data acquisition protocols.