Current‐induced alternating reversed dual‐echo‐steady‐state for joint estimation of tissue relaxation and electrical properties

Lee, Hyunyeol; Sohn, Chul Ho; Park, Jaeseok

doi:10.1002/mrm.26350

Cited by 4 publications

(5 citation statements)

References 26 publications

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“…The unbalanced SSFP mechanism and its variants have been used in numerous quantitative MRI methods, including measurement of relaxation parameters, 37,38 electrical conductivity, 38,39 diffusion-related parameters, 40 and regional ), while the limits of agreement (dotted lines; mean ± 1.96 × SD of differences) encompass zero temperature. 41 Particularly in diffusion MRI applications, the SSFP-ECHO configuration, due to its high sensitivity to motion, has been explored as a time-and gradient-efficient alternative to SE-based techniques.…”

Section: Discussionmentioning

confidence: 99%

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Alternating unbalanced SSFP for 3D mapping of the human brain

Lee

Wehrli

2020

Magnetic Resonance in Med

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Purpose Measuring the transverse‐relaxation rate R2′ provides valuable information in quantitative evaluation of tissue microstructure, for example, in terms of oxygenation levels. Here, we propose an alternating unbalanced SSFP pulse sequence for rapid whole‐brain 3D R2′ mapping. Methods Unlike currently practiced, spin echo–based R2′ measurement techniques, the proposed method alternates between SSFP‐FID and SSFP‐ECHO modes for rapid 3D encoding of transverse relaxation rates expressed as R2 + R2′ and R2‐R2′. Z‐shimming gradients embedded into multi‐echo trains of each SSFP module are designed to achieve relative immunity to large‐scale magnetic‐field variations (ΔB0). Appropriate models for the temporal evolution of the two groups of SSFP signals were constructed with ΔB0‐induced modulations accounted for, leading to ΔB0‐corrected estimation of R2, R2′, and R2∗ (= R2 + R2′). Additionally, relative magnetic susceptibility (Δχ) maps were obtained by quantitative susceptibility mapping of the phase data. Numerical simulations were performed to optimize scan parameters, followed by in vivo studies at 3 T in 7 healthy subjects. Measured parameters were evaluated in six brain regions, and subjected to interparameter correlation analysis. Results The resultant maps of R2′ and additionally derived R2, R2∗, and Δχ all demonstrated the expected contrast across brain territories (eg, deep brain structures versus cortex), with the measured values in good agreement with previous reports. Furthermore, regression analyses yielded strong linear relationships for the transverse relaxation parameters (R2′, R2, and R2∗) against Δχ. Conclusion Results suggest feasibility of the proposed method as a practical and reliable means for measuring R2′, R2, R2∗, and Δχ across the entire brain.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Alternating unbalanced SSFP for 3D mapping of the human brain

Lee

Wehrli

2020

Magnetic Resonance in Med

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“…Reconstruction was also more involved in than for this EPI‐based method. In Lee et al , the SNR or SNR per unit time measures were considered. Because the SNR measures, imaging techniques, and imaging times are so different, it would be difficult to directly compare these measures between this technique and that found in .…”

Section: Discussionmentioning

confidence: 99%

“…In Lee et al , the SNR or SNR per unit time measures were considered. Because the SNR measures, imaging techniques, and imaging times are so different, it would be difficult to directly compare these measures between this technique and that found in . However, the SNR per time quantities may be useful in comparing different shot number data within the framework used here.…”

Section: Discussionmentioning

confidence: 99%

Multishot echo‐planar MREIT for fast imaging of conductivity, current density, and electric field distributions

Chauhan

Shankar

Kumar

et al. 2017

Magnetic Resonance in Med

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Purpose: Magnetic resonance electrical impedance tomography (MREIT) sequences typically use conventional spin or gradient echo-based acquisition methods for reconstruction of conductivity and current density maps. Use of MREIT in functional and electroporation studies requires higher temporal resolution and faster sequences. Here, single and multishot echo planar imaging (EPI) based MREIT sequences were evaluated to see whether high-quality MREIT phase data could be obtained for rapid reconstruction of current density, conductivity, and electric fields. Methods: A gel phantom with an insulating inclusion was used as a test object. Ghost artifact, geometric distortion, and MREIT correction algorithms were applied to the data. The EPI-MREIT-derived phase-projected current density and conductivity images were compared with simulations and spinecho images as a function of EPI shot number. Results: Good agreement among measures in simulated, spin echo, and EPI data was achieved. Current density errors were stable and below 9% as the shot number decreased from 64 to 2, but increased for single-shot images. Conductivity reconstruction relative contrast ratios were stable as the shot number decreased. The derived electric fields also agreed with the simulated data. Conclusions: The EPI methods can be combined successfully with MREIT reconstruction algorithms to achieve fast imaging of current density, conductivity, and electric field. Magn Reson Med 79:71-82,

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“…Nevertheless, the utility of these SE-based methods has been limited by the impractically long scan times and low phase sensitivity. To address these issues in SE-based MREIT, alternating steady-state free precession (SSFP) MREIT has been suggested [23,26]. Compared with SE MREIT, the method enables rapid conductivity imaging while yielding high phase sensitivity resulting from the nonlinear behavior of SSFP signals in response to alternating current injection.…”

Section: Introductionmentioning

confidence: 99%

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

Lee

Park

2022

Tomography

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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.

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Current‐induced alternating reversed dual‐echo‐steady‐state for joint estimation of tissue relaxation and electrical properties

Cited by 4 publications

References 26 publications

Alternating unbalanced SSFP for 3D mapping of the human brain

Alternating unbalanced SSFP for 3D mapping of the human brain

Multishot echo‐planar MREIT for fast imaging of conductivity, current density, and electric field distributions

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

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