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Abstract:
Purpose
Information on the electrical tissue conductivity might be useful for the diagnosis and characterization of pathologies such as tumors [1]. MRCDI and MREIT are two emerging non-invasive techniques for imaging of weak currents and ohmic conductivities. In this study, we demonstrated human in vivo brain MRCDI to pave the way for its clinical use [2], [3].
Methods
In short, weak alternating currents up to 1–2 mA are injected into human head in synchrony with tailored phase-sensitive MRI. The currents create a magnetic field
, which shifts the precession frequency of the magnetization and modulates the acquired MR images. The acquired images are used to measure and reconstruct the current flow and conductivity distributions. We employed a steady-state free precession free-induction-decay (SSFP-FID) sequence in five subjects, and injected currents of 1 mA by an MR-conditional current source via electrodes attached to the scalp (two current profiles: Right-left (RL), electrodes placed near the temporoparietal junctions; anterior-posterior (AP), one attached to the forehead and one above the inion). Additionally, an ultra-short-echo-time sequence was performed to track the feeding cables for correcting the stray magnetic fields induced by cable currents. Corrected
measurements were used to calculate current flow distributions and compared with Finite-Element simulations of the current flow based on individualized head models [4].
Results
The current-induced magnetic field with was reliably measured and the reconstructed current flows showed good agreement with the simulations (average coefficient of determination R2= 71%). The injected current flow differed substantially among individuals according to the electrode placements and anatomical differences. The calculated currents are stronger in CSF-filled highly conductive regions, e.g. the longitudinal fissure.
Conclusions
The strong correlation between the simulations and measurements validates the accuracy of the method and demonstrates the potential of the method for determining accurate brain tissue conductivities. These initial current flow recordings pave the way for human brain MREIT that might complement standard MR methods for tumor characterization.
