Seed-based d mapping (formerly Signed differential mapping) or SDM is a statistical technique created by Joaquim Radua for meta-analysis studies assessing differences in brain activity or structure via neuroimaging techniques such as fMRI, VBM, DTI or PET.
It may also refer to a specific piece of software created by the SDM Project to carry out such meta-analyses.
First, coordinates of cluster peaks (e.g. the voxels where the differences between patients and healthy controls were highest), and statistical maps if available, are selected according to SDM inclusion criteria.
Finally, individual study maps are meta-analyzed using different tests to complement the main outcome with sensitivity and heterogeneity analyses.
[3] Pre-processing of statistical parametric maps is straightforward, while pre-processing of reported peak coordinates requires recreating the clusters of difference by means of an un-normalized Gaussian Kernel, so that voxels closer to the peak coordinate have higher values.