FIGURE 2.

General scheme of a voxel-wise regression of covariates harmonization approach. For these methods the voxel intensity of the diffusion metric maps (y_spv, the intensity for a specific site s, subject p and voxel v) is modeled as a combination of a voxel-wise intercept (α_v), a voxel-wise slope (β_v) multiplied by a model-specific dependent variable (x_spv), and an error component (ε_spv). Each of the regression of covariates approaches will have a different model and dependent variable to describe the biological and site-related effects on the diffusion metric intensities. Next, the estimated coefficients are used to compute the new harmonized diffusion intensity values ($y_{\text{spv}}^{\text{harmonized}}$).