Current density imaging sequences with separation of mobile-ion current from immobile-ion current

Three sequences for electric current density imaging (CDI) are studied by testing their ability to selectively detect the electric current of different types of charge carriers. Two of the methods are standard DC-CDI and AC-CDI sequences, and a new AC-DC-CDI sequence is also introduced. The methods rely on the application of square voltage pulses in combination with refocusing RF pulses that can, depending on their position with respect to the voltage pulses, eliminate resistive, capacitive or neither of the current components from the detection pathway. It is demonstrated by experiments on a model system that the DC-CDI sequence detects only the resistive current of mobile ions, the AC-DC-CDI sequence detects only the capacitive current of fixed ions, while the AC-CDI sequence detects both current components. The three sequences introduce a new MRI contrast mechanism that depends on the ion mobility of the sample. As such, the methods may play an important role in the study of electric conductivity phenomena in biological systems.