Experimental performance evaluation of multi‐echo ICNE pulse sequence in magnetic resonance electrical impedance tomography

Abstract

Latest experimental results in magnetic resonance electrical impedance tomography (MREIT) demonstrated high-resolution in vivo conductivity imaging of animal and human subjects using imaging currents of 5 to 9 mA. Externally injected imaging currents induce magnetic flux density distributions, which are affected by a conductivity distribution. Since we extract the induced magnetic flux density images from MR phase images, it is essential to reduce noise in the phase images. In vivo human and disease model animal experiments require reduction of imaging current amplitudes and scan times. In this article, we investigate a multi-echo based MREIT pulse sequence where we utilize a remaining time after the first echo within one TR to obtain more echo signals. It also allows us to prolong the total current injection time. From phantom and animal imaging experiments, we found that this method significantly reduces the noise level in measured magnetic flux density images. We describe experimental validation of the multi-echo sequence by comparing its performance with a single-echo method using 3 mA imaging currents. The proposed method will be advantageous for an imaging region with long T2 values such as the brain and knee. Depending on T2 values, we suggest using two or three echoes in future experimental studies. Magn Reson Med 66:957-965, 2011. V C 2011 Wiley-Liss, Inc.

Numerical Simulations of MREIT Conductivity Imaging for Brain Tumor Detection

“…More sensitive and faster pulse sequences are currently in development [8, 36] and may further improve phase data, signal-to-noise-ratio (SNR), and sensitivity. The use of multiple RF coils and newer, lower-noise systems should further enhance SNR.…”

“…Voltage solutions were computed on the head domain, and then converted to magnetic flux density ( B z ) values within voxels of the size of 1.40 × 1.40 × 4 mm 3 using the Biot-Savart law [7, 8] or a fast Fourier transform method [29]. Data were computed over a 180 × 180 mm 2 field of view (FOV) and 8 slices in total were simulated, each slice having a thickness of 4 mm.…”

“…Magnetic resonance electrical impedance tomography (MREIT) is a technique that uses MRI to measure the internal magnetic flux density induced by externally injected currents [6–8]. Since the magnetic flux density perturbs the main field of an MRI scanner, one can obtain the z -component of the induced magnetic flux density ( B z ) by rescaling MR phase images [9–11].…”

“…As a result, injected currents may induce a small phase signal, high noise level and low signal-to-noise-ratio (SNR) in brain tissue. Since the phase signals measured in MREIT may be quite small, SNR can be improved by increasing the imaging current amplitude or imaging time [8]. As in many other applications, intrinsic noise levels may be reduced by increased averaging or using higher field strengths.…”

CoReHA 2.0: A Software Package forIn VivoMREIT Experiments

“…Based on the harmonic B z algorithm [5], CoReHA supports all procedures from the preprocessing of raw data to conductivity imaging through the intuitively apprehensible graphic user interface, more specifically, data conversion of raw k -space data, data verification, segmentation tools for numerical computation, solvers of forward/inverse problems using finite element methods, and 2D/3D data view as well as histogram. This software has been a major tool to facilitate multilateral studies for MREIT and has brought out successful reconstruction of conductivity imaging in many researches [4, 6–8]. …”