MEASUREMENT OF NONUNIFORM CURRENT-DENSITY BY MAGNETIC-RESONANCE

Conventional magnetic resonance imagers can measure the electric current density in any substance which can be imaged by nuclear magnetic resonance. This current density image is created by measuring the magnetic field arising from these currents and taking its curl. These magnetic fields are proportional to the phase component of a complex magnetic resonance image. Measurements of all three components of a quasistatic nonuniform current density in a phantom are described. Expected current density calculations from a numerical solution for the magnetic field which was created by the phantom are presented for comparison. The results of a numerical simulation of the experiment, which used this field solution and which included the effects of slice selection and sampling, are also presented. The experimental and simulated results are quantitatively compared. It is concluded that the principle source of systematic error was the finite slice thickness which causes blurring of boundaries. The method could be used to study the spatial distribution of currents injected by an external source if the currents are repetitive and can be synchronized with the magnetic resonance imaging sequence. Physical rotation of the conducting sample is required.