Read out recent editorial on the need to control model methods. 

1) Beginning with high-resolution (e.g. 1 mm) anatomical scans, the entire model work flow should preserve precision.  Any Finite Elemet (FE) human head model is limited by the precision and accuracy of tissue dimensions (along with individual segmentation mask quality) and conductivity values incorporated (inhomogeneity and anisotropy). One hallmark of precision is that the cortical surface used in the final FEM solver should capture realistic sulci and gyri.

2) Simultaneously, a priori knowledge of tissue anatomy and factors known to shape current flow should be applied to further refine segmentation. Particularly critical are discontinuities not present in nature that result from limited scan resolution; notably both unnatural perforations in planar tissues (e.g. holes in CSF where brain contacts skull, misrepresented skull fissures, ventricular architecture….) and microstructures (e.g. incomplete or voxelized vessels) can produce significant aberrations in predicted current flow. Moreover, incorporation of multiple different tissue masks (e.g. eye sclera, cornea, glands, midbrain...) without reliable reported human conductivity values in literature (especially at DC frequency) may also lead to errors.

Thus addition of complexity without proper parameterization can evidently decrease prediction accuracy. An improper balance between these factors can lead to distortions in brain current flow of an order of magnitude or more, with the most appropriate methodology (ranging from concentric spheres to individualized models) ultimately depending on the clinical question being addressed.