Sensitivity of MRI for directly detecting neuronal electrical activities in rat brain slices

We developed an experimental setup for magnetic resonance imaging (MRI) of rat brain slices maintained in a hemoglobin-free medium and showed that the MRI system has a sensitivity to magnetic fields of 10^-11 T. The originally developed non-magnetic sample holder consisted of a microelectrode array for recording neuronal potentials and perfusing channels for the medium. Because of the hemoglobin-free condition, the magnetic fields could be distinguished from the baseline signal fluctuations due to hemoglobin. A theoretical estimation of the signal-to-noise ratio showed a sensitivity of 3.3 × 10^-10 T. Parameter optimization using a 7-T MRI system with the developed sample holder resulted in an experimental sensitivity of 4.0 × 10^-10 T. These MRI sensitivities potentially enable us to detect weak magnetic fields arising from neuronal activities, and are sufficiently high for detecting neuronal magnetic fields of 1.4 × 10^-11 T generated in rat brain slices by averaging signals 810 times.