Our methods paper on AC/PC to MNI conversion has been summarized in the following resources:

Read our blog post explaining AC/PC to MNI conversions in detail here
A brief talk held at AAN 2017 can be found here

Furthermore, the methodology is described in the paper listed below.

Horn, A., Kühn, A. A., Merkl, A., Shih, L., Alterman, R., & Fox, M. (2017). Probabilistic conversion of neurosurgical DBS electrode coordinates into MNI space. NeuroImage, 150, 395–404. 

The methodology is implemented in the AC/PC conversion tool supplied within Lead-DBS.

Tools menu used to open the AC/PC to MNI conversion tool

AC/PC to MNI coordinate conversion tool as implemented in Lead-DBS. The warps are based on selected subjects/patients that must be normalized using Lead-DBS first. Alternatively, the open license IXI-Dataset may be used to perform conversions and Lead-DBS will selected subjects matched for age as described in Horn et al. 2017.