Harmonization of Multi-Site DTI and NODDI Data Using the Combined Association Test [Proceedings of the 2022 Young Investigator Award]

When analyzing the multi-site diffusion MRI (dMRI) data, metrics should be harmonized to remove the site effect. In this study, we applied the combined association test (ComBat), which used the regression of covariates with an empirical Bayes framework for diffusion metrics based on diffusion tensor imaging (DTI), neurite orientation dispersion, and density imaging (NODDI). The results showed that the ComBat could harmonize the site-related effects in DTI and NODDI metrics based on multi-site dMRI while preserving the biological information of the participant, such as sex differences and correlation with age. Thus, the ComBat could be applied in large multi-site studies to identify subtle white matter changes.