  Extracting quantitative information of neuronal signals by non-invasive
imaging is an outstanding challenge for understanding brain function and
pathology. However, state-of-the-art techniques offer low sensitivity to deep
electrical sources. Stimulus induced rotary saturation (SIRS) is a recently
proposed magnetic resonance imaging (MRI) sequence that detects oscillatory
magnetic fields using a spin-lock preparation. Phantom experiments and
simulations proved its efficiency and sensitivity, but the susceptibility of
the method to field inhomogeneities is still not well understood. In this
study, we simulated and analyzed the dynamic of three spin-lock preparations
and their response to field inhomogeneities in the presence of a resonant
oscillating field. We show that the composite spin-lock preparation is more
robust against field variations within the double resonance effect. In
addition, we tested the capability of the chosen composite spin-lock
preparation to recover information about the spectral components of a composite
signal. This study sets the bases to move one step further towards the clinical
application of MR-based neuronal current imaging.
