In Vivo High-ResolutionConductivity Imaging of the Human Leg Using MREIT: The First Human Experiment

Abstract

We present the first in vivo cross-sectional conductivity image of the human leg with 1.7 mm pixel size using the magnetic resonance electrical impedance tomography (MREIT) technique. After a review of its experimental protocol by an Institutional Review Board (IRB), we performed MREIT imaging experiments of four human subjects using a 3 T MRI scanner. Adopting thin and flexible carbon-hydrogel electrodes with a large surface area and good contact, we could inject as much as 9 mA current in a form of 15 ms pulse into the leg without producing a painful sensation and motion artifact. Sequentially injecting two imaging currents in two different directions, we collected induced magnetic flux density data inside the leg. Scaled conductivity images reconstructed by using the single-step harmonic B(z) algorithm well distinguished different parts of the subcutaneous adipose tissue, muscle, crural fascia, intermuscular septum and bone inside the leg. We could observe spurious noise spikes in the outer layer of the bone primarily due to the MR signal void phenomenon there. Around the fat, the chemical shift of about two pixels occurred obscuring the boundary of the fat region. Future work should include a fat correction method incorporated in the MREIT pulse sequence and improvements in radio-frequency coils and image reconstruction algorithms. Further human imaging experiments are planned and being conducted to produce conductivity images from different parts of the human body.

Direct detection of neural activity in vitro using magnetic resonance electrical impedance tomography (MREIT)

“…In vivo imaging has been tested in MREIT in some studies, for example (Kim et al, 2009) but no in vivo fMREIT studies have yet been tried. One advantage that fMREIT may have over ncMRI is that it may be possible to detect activity in complex neural architecture because contrast is controlled by a scalar rather than vector parameter.…”

MREIT experiments with 200 µA injected currents: a feasibility study using two reconstruction algorithms, SMM and harmonicBZ

“…Despite these potential clinical applications, there are only a few in vivo MREIT studies reported (Muftuler et al 2006b, Kim et al 2008, Kim et al 2009). Probably the most important obstacle to the clinical application of MREIT is the limitation on the amount of electrical current that can be safely injected to a patient.…”

“…Recently, several investigators explored whether the IEC601 standards impose unnecessarily strict limits in impedance imaging experiments (Gilad et al 2007 and Kim et al 2009). Gilad et al (2007) suggested that this limit could possibly be increased up to 200μA for on-skin and 600μA for recessed electrodes for conductivity imaging of the head at low frequencies.…”

Reconstruction of apparent orthotropic conductivity tensor image using magnetic resonance electrical impedance tomography

“…Since we mainly use carbon-hydrogel electrodes, the conductivity of hydrogel will be used as the reference value. 28 Using two projected current densities J ';P ; ' ¼ 1; 2, we will design an over-determined matrix system by linking the internal orthotropic conductivity value at each pixel to the known conductivity. To recover two unknowns of r 11 and r 22 , we will apply the dual-loop method.…”