Optimization of current injection pulse width in MREIT

In MREIT (magnetic resonance electrical impedance tomography), we inject electrical current into a volume conductor to induce a distribution of a magnetic flux density. By measuring the internal magnetic flux density data using an MR scanner, we reconstruct images of cross-sectional conductivity and current density distributions. One of the most important technical problems in MREIT is to reduce the noise level in measured magnetic flux density data since it limits the reconstructed conductivity image quality. The noise level is inversely proportional to the current injection pulse width and the signal-to-noise ratio of MR magnitude images. Knowing that we cannot simultaneously increase both factors for a chosen echo time, we show that there is an optimal current injection pulse width minimizing the noise level. Experimental results demonstrate that the optimal current injection pulse width and appropriately chosen data acquisition time considerably reduce the noise standard deviation of measured magnetic flux density data. Even though there may occur undesirable side-effects with an increased data acquisition time, we found that the the pulse sequence with the optimal timing outperforms conventional method in terms of the noise level and conductivity image quality.