Toward a magnetic resonance electrical impedance tomography in ultra-low field: A direct magnetic resonance imaging method by an external alternating current

Measuring the electrical impedance of biological tissues in a low frequency range is challenging. Here, we have conducted a superconducting quantum interference device-based microtesla magnetic resonance (MR) imaging study. To obtain an MR image caused by an injected alternating current (ac), we utilized the direct resonance method in which the nuclear spins resonate with the ac magnetic field generated by the external ac current. This method requires an adiabatic pulse and non-adiabatic step-down pulse techniques. The experimental and simulation results agree well with each other and show the feasibility of low-frequency magnetic resonance electrical impedance tomography in the kHz range.