Magnetic flux density measurement with balanced steady state free precession pulse sequence for MREIT: A simulation study

Minhas, Atul S.; Woo, Eung Je; Lee, Soo Yeol

doi:10.1109/iembs.2009.5335084

Cited by 14 publications

(12 citation statements)

References 9 publications

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“…Phantom experiments have shown that SNR levels may be increased by a factor of around 1.7 by use of this technique. We may also take advantage of the balanced SSFP (steady state free precession) pulse sequence, which is highly sensitive to small off-resonance phase changes (Minhas et al 2009). Special care must be given to the main field inhomogeneity in this case.…”

Section: Discussionmentioning

confidence: 99%

Can high-field MREIT be used to directly detect neural activity? Theoretical considerations

2010

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We sought to determine the feasibility of directly studying neural tissue activity by analysis of differential phase shifts in MRI signals that occurred when trickle currents were applied to a bath containing active or resting neural tissue. We developed a finite element bidomain model of an aplysia abdominal ganglion in order to estimate the sensitivity of this contrast mechanism to changes in cell membrane conductance occurring during a gill-withdrawal reflex. We used our model to determine both current density and magnetic potential distributions within a sample chamber containing an isolated ganglion when it was illuminated with current injected synchronously with the MR imaging sequence, and predicted the resulting changes in MRI phase images. This study provides the groundwork for attempts to image neural function using Magnetic Resonance Electrical Impedance Tomography (MREIT). We found that phase noise in a candidate 17.6 T MRI system should be sufficiently low to detect phase signal differences between active and resting membrane states at resolutions around 1 mm3. We further delineate the broad dependencies of signal to noise ratio on activity frequency, current application time and active tissue fractions, and outline strategies that can be used to lower phase noise below that presently observed in conventional MREIT techniques. We also propose the idea of using MREIT as an alternative means of studying neuromodulation.

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Section: Discussionmentioning

confidence: 99%

Can high-field MREIT be used to directly detect neural activity? Theoretical considerations

2010

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“…We, therefore, assumed that the MR magnitude image is independent of the main fieldinhomogeneity, TR, and flip angle. However, if we consider a gradient echo based pulse sequence [12] and other fast pulse sequences [15], the signal would be dependent on θ 0 , θ rf , T 1 and T 2 distributions, TR, TE, and flip angle. We plan to extend the MREIT simulator to those cases.…”

Section: Discussionmentioning

confidence: 99%

“…An offresonance phase θ may also contribute to Φ [14]. Depending on a chosen pulse sequence, Φ may be either a linear or nonlinear function of θ Bz or θ or both [13,15]. Assuming certain δ and θ distributions and using computed B z , we can numerically simulate the synthetic k-space signal S ± in Eq.…”

Section: Simulation Of Mreit Data Acquisitionmentioning

confidence: 98%

“…The magnitude image M is a function of phases due to RF (θ rf ) and main field inhomogeneity (θ 0 ), tissue relaxation time constants T 1 and T 2 , imaging parameters TR and TE, and flip angle [12][13][14][15]. Choosing proper TR and TE and assuming certain flip angle, θ 0 , θ rf , T 1 and T 2 distributions, we can simulate an MRI scan to image M in Eq.…”

Section: Simulation Of Mreit Data Acquisitionmentioning

confidence: 99%

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Three-dimensional MREIT simulator of static bioelectromagnetism and MRI

et al. 2011

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Purpose Magnetic resonance electrical impedance tomography (MREIT) aims to produce high-resolution cross-sectional images of a conductivity distribution inside the human body. We perform conductivity image reconstructions based on a relation between the conductivity distribution and induced magnetic flux density distributions subject to externally injected currents. This induced magnetic flux density is measured in MREIT using an MRI scanner. To facilitate MREIT research, we need a numerical simulator including static bioelectromagnetism and MRI data collection process. In this paper, we describe the development of a threedimensional MREIT simulator (MREITSim). Methods We describe various features of MREITSim including geometry modeling, meshing, finite element modeling and numerical computations of magnetic flux density and k-space MR data. We demonstrate the underlying bioelectromagnetic phenomena and MR data collection process using phantom models of without and with anomaly. We illustrate effects of noise in MR data and echo time on magnetic flux density computations. Results We demonstrate numerical computations of current density and magnetic flux density distributions for current injections orthogonal to z-direction, the direction of the main magnetic field of an MRI scanner. The k-space MREIT data generation procedure is illustrated using a phantom model with an insulating anomaly. Conclusions The simulator functions as a virtual MREIT scanner and provides quantitative numerical results of intended experimental studies. We suggest the simulator as a basic research tool for future MREIT studies of its theory, algorithm, experimental techniques and pulse sequence design.

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“…The single-echo ICNE pulse sequence has been widely used in MREIT to produce postmortem and in vivo conductivity images of animal and human subjects using injection currents of a few milliamperes and scan times of several tens of minutes (16)(17)(18)(19). To reduce the current amplitude and scan time while keeping the image quality, we need to incorporate more sophisticated pulse sequences such as FSE, EPI, and SSFP (29). In addition, we should investigate applying parallel imaging techniques using multi-channel RF coils (30).…”

Section: Discussionmentioning

confidence: 99%

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

Minhas¹,

Jeong²,

Kim³

et al. 2011

Magnetic Resonance in Med

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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.

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Magnetic flux density measurement with balanced steady state free precession pulse sequence for MREIT: A simulation study

Cited by 14 publications

References 9 publications

Can high-field MREIT be used to directly detect neural activity? Theoretical considerations

Can high-field MREIT be used to directly detect neural activity? Theoretical considerations

Three-dimensional MREIT simulator of static bioelectromagnetism and MRI

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

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