Microscopic investigation of the resonant mechanism for the implementation of nc-MRI at ultra-low field MRI.

In this paper the possible use of the resonant mechanism between some spectral components of the neuronal activity and the spin dynamics in ultra-low field MRI experiments--for the implementation of the nc-MRI techniques and proposed by Kraus et al., 2008--is investigated by means of "realistic" simulations of the neuronal activity of a modelled neuronal network. Previously characterized digital neurons are used to reproduce neuronal currents based on biophysical details and the distribution of the local magnetic field inside a MRI cubic voxel (having a dimension of 1.2 mm) is evaluated. The properties of the water proton spin dynamics as a consequence of the neuronal field and of external applied fields are extrapolated integrating the Bloch equations. The characteristics of the expected MR signals are discussed in relation to the specifics of the NMR sequence used and to the properties of the neuronal activity. The great potentialities of the technique are provided by: a) the possible easy implementation of the technique, b) the possible cheap instrumentation required; c) the flexibility of the ultra-low field systems.