SNR-Enhanced, Rapid Electrical Conductivity Mapping Using Echo-Shifted MRI.

Hyunyeol Lee,Jaeseok Park

doi:10.3390/tomography8010031

Abstract

Magnetic resonance electrical impedance tomography (MREIT) permits high-spatial resolution electrical conductivity mapping of biological tissues, and its quantification accuracy hinges on the signal-to-noise ratio (SNR) of the current-induced magnetic flux density (Bz). The purpose of this work was to achieve Bz SNR-enhanced rapid conductivity imaging by developing an echo-shifted steady-state incoherent imaging-based MREIT technique. In the proposed pulse sequence, the free-induction-decay signal is shifted in time over multiple imaging slices, and as a result is exposed to a plurality of injecting current pulses before forming an echo. Thus, the proposed multi-slice echo-shifting strategy allows a high SNR for Bz for a given number of current injections. However, with increasing the time of echo formation, the Bz SNR will also be compromised by T2*-related signal loss. Hence, numerical simulations were performed to evaluate the relationship between the echo-shifting and the Bz SNR, and subsequently to determine the optimal imaging parameters. Experimental studies were conducted to evaluate the effectiveness of the proposed method over conventional spin-echo-based MREIT. Compared with the reference spin-echo MREIT, the proposed echo-shifting-based method improves the efficiency in both data acquisition and current injection while retaining the accuracy of conductivity quantification. The results suggest the feasibility of the proposed MREIT method as a practical means for conductivity mapping.

Highlights

Electrical conductivity inside the living body is determined by a number of factors, including its underlying cellular structure, ion mobility and concentration, and molecular composition [1,2]
Electrical impedance tomography (EIT) is a non-invasive imaging technique that permits the estimation of the electrical conductivity distribution inside an imaging object [15,16]
In EIT, current injection is applied to the imaging object through multiple surface electrodes, and induced voltages are measured to reconstruct cross-sectional conductivity maps based on a nonlinear inverse solution

Summary

Introduction

Electrical conductivity inside the living body is determined by a number of factors, including its underlying cellular structure, ion mobility and concentration, and molecular composition [1,2]. Electrical conductivity information has been employed in a range of applications such as EEG and MEG neuronal source localization [3,4,5], quantitative monitoring of neuronal depolarization [6], ion mobility imaging [7,8,9], estimation of current distribution during therapeutic electrical stimulation [10,11,12,13], and evaluation of brain abnormalities [14]. Electrical impedance tomography (EIT) is a non-invasive imaging technique that permits the estimation of the electrical conductivity distribution inside an imaging object [15,16]. In EIT, current injection is applied to the imaging object through multiple surface electrodes, and induced voltages are measured to reconstruct cross-sectional conductivity maps based on a nonlinear inverse solution. It is difficult to achieve high spatial resolution conductivity mapping with a limited number of electrodes [16]

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Methods

Results

Conclusion