Cross-site Quantitative MRI Harmonization: The Impact on Age Modeling in Health and Disease

Cross-site quantitative MRI (qMRI) studies are hindered by site-related variability, particularly when integrating cohorts with varying acquisition protocols and biological variables, such as age. Such batch effects can obscure accurate biological signals, thus affecting normative age modeling and clinical interpretations of pathology. This study aimed to (i) compare the harmonization performance of multiple strategies across multi-site cohorts with matched or unmatched qMRI protocols; (ii) quantify the impact of harmonization on normative age modelling across cohorts with comparable or partially overlapping age ranges; and (iii) examine whether clinically relevant deviations are preserved. This DSC includes the statistical scripts, quantitative MRI metrics used in this study.