Induced Current Magnetic Resonance Electrical Conductivity Imaging With Oscillating Gradients

Abstract

In this paper, induced current magnetic resonance electrical impedance tomography (ICMREIT) by means of current induction due to time-varying gradient fields of magnetic resonance imaging (MRI) systems is proposed. Eddy current and secondary magnetic flux density distributions are calculated for a numerical model composed of a z-gradient coil and a cylindrical conductor. An MRI pulse sequence is developed for the experimental evaluation of ICMREIT on a 3T MRI scanner. A relationship between the secondary magnetic flux density and the low-frequency (LF) MR phase is formulated. Characteristics of the LF phase, the eddy current, and the reconstructed conductivity distributions based on the simulated and the physical measurements are in agreement. Geometric shifts, which may contaminate the LF phase measurements, are not observed in the MR magnitude images. Low sensitivity of the LF phase measurements is a major limitation of ICMREIT towards clinical applications. The reconstructed conductivity images are rough estimates of true conductivity distribution of the experimental phantoms. Although the experimental results show that ICMREIT is safe and potentially applicable, its measurement sensitivity and reconstruction accuracy need to be optimized in order to improve the technique towards clinical applications.

Quantitative Analysis of Electrical Current Effect on Magnetic Resonance Image Tissue Intensity

“…Basic of MREIT is the alteration of electrical conductivity distribution inside the biological object when injected with electrical current. This alteration is affected by molecular composition, cellular structure, concentration, and mobility of chemical components intracellular, extracellular fluids, and temperature [20,21,22].…”

Mapping oscillating magnetic fields around rechargeable batteries

“…A number of MRI methods have been developed to detect electric currents via measurements of the corresponding magnetic fields using synchronized pulse sequence elements [19,20,21,22,23,24,25]. An approach based on a tuned spin-lock field exploits the coherent interaction between the spinlock pulse and a fluctuating magnetic field produced by electrical currents [19].…”

“…In particular, this approach exhibits problems at low frequencies due to RF imperfections and T 1ρ relaxation. Other techniques comprise current density imaging (CDI) sequences [21,22,23] and steady state free precession (SSFP) approaches [20], both based on exploiting phase changes in the magnetic resonance signals caused by current-generated local magnetic magnetic fields. However, both approaches require precise synchronization of pulse sequence elements with the AC frequency.…”