MinR 10/20 system: Quantitative and reproducible cranial landmark setting method for MRI based on minimum initial reference points.

Abstract Background The international 10/20 system is not only a fundamental method for describing positioning for electroencephalography (EEG), but also provides intermediate cranial landmarks for the probabilistic spatial registration methods that use a reference-MRI database. However, the presence of the inion, one of the four initial reference landmarks of the international 10/20 system, is inconspicuous and can be difficult to locate on MRIs. New method The MinR 10/20 system utilizes only three initial reference points, the nasion (Nz) and the right and left preauricular points (AR and AL), but does not employ the inion (Iz). With the MinR 10/20 system, first the most posterior point on the occipital protuberance, IIz (Imitated Iz), is identified as an exploratory alternative to the Iz point. Next, the other landmarks are calculated according to the conventional international 10/20 system referring to these four reference points (Nz, AL, AR and IIz). Results Holistic tendencies for landmark position estimations on the heads and cortices in MNI space did not vary greatly between MinR and international 10/20 systems. Comparison with existing methods A comparison of MinR and international 10/20 systems applied to seventeen adult head MRIs revealed little variance in holistic tendencies for landmark position estimations on head and cortex surfaces in the MNI coordinate system. Furthermore, variability was smaller with the MinR 10/20 system than with the conventional international 10/20 system. Conclusions The MinR 10/20 system proved to be a practical alternative to the conventional international 10/20 system in modern computational spatial analysis for scalp-based brain mapping methods.