Challenges for detection of neuronal currents by MRI.

Neuronal current MRI (nc-MRI) is an imaging method that directly maps magnetic field changes caused by neuronal currents with, at the same time, a high spatial and temporal resolution. A viable nc-MRI method would be of great benefit, both for the study of human brain function and for clinical applications in the field of epilepsy, especially for the noninvasive presurgical mapping of epileptogenic foci. A survey of fundamental issues in nc-MRI is reviewed, and challenges for future developments of the method are described within this context. Particularly, an overview of the models for signal generation is given, and the origin and physiology of different sources of neuronal currents are described. Prospects for predicting neuronal currents by electromagnetic field mapping and using this information, both a priori and a posteriori, for nc-MRI are considered. Ways of increasing specificity in nc-MRI by minimizing secondary hemodynamic and metabolic effects are described as well as means of optimizing the nc-MRI method for pushing the detection limit. Previously published works are described within these categories and future directions for nc-MRI are proposed.