Electric Current Detection Based on the MR Signal Magnitude Decay

Abstract

Purpose: Conventional current density imaging method, which relies on the detection of the magnetic field induced by the current in an image phase, is demanding and difficult to perform. In this study, a much simpler signal-magnitude-decay (SMD)-based current detection method is proposed.

Methods: Conductive test and biological samples were imaged at various TE times using the gradient- or spin-echo imaging sequences with superimposed constant or bipolar currents, respectively. The SMD curve was sampled for each image voxel, which enabled voxel-vise current density calculation by fitting an appropriate SMD model curve to the measured SMD curve. Effect of the voxel size on the signal decay and precision of the current density calculation was studied as well.

Results: It was shown theoretically, as well as verified by experiments on test and biological samples, that the current flowing though the sample creates an inhomogeneous magnetic field, which, as a consequence has a faster signal decay. Estimated current density from the measured signal decay increase agreed reasonably well with the actual current density, especially with the larger voxel sizes and longer times to signal acquisition. The sensitivity of the SMD method is up to $1/\sqrt{6}$ the sensitivity of the current density imaging method.

Conclusion: SMD method of current detection is not limited to any particular sample orientation or geometry, and any pulse sequence capable of acquisition of the current-induced signal evolution in a voxel can be used for it. This widens the scope of its application from tissues to in vivo studies on animals and humans.

Keywords: current-induced magnetic field gradient; electric current detection; gradient-echo imaging; signal magnitude decay.