Time-domain finite-difference/finite-element hybrid simulations of radio frequency coils in magnetic resonance imaging

Wang, Shumin; Duyn, Jeff H.

doi:10.1088/0031-9155/53/10/016

Cited by 13 publications

(9 citation statements)

References 22 publications

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“…Average and local SARs inside the human head were simulated under our experimental conditions using a custom-designed finite difference in time domain/finite element method (FDTD/FEM) program developed in-house (20,21). In FEM, the birdcage coil was modeled according to the actual dimensions with unstructured tetrahedral meshes.…”

Section: Methodsmentioning

confidence: 99%

¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

Zhang

Wang

et al. 2010

NMR in Biomedicine

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Previously, we devised a novel strategy for in vivo 13C MRS using [2-13C]glucose infusion and low-power proton decoupling, and proposed that this strategy could be used to acquire 13C MR spectra from the frontal lobe of the human brain. Here, we demonstrate, for the first time, in vivo 13C MRS of human frontal lobe acquired at 3 T. Because the primary metabolites of [2-13C]glucose can be decoupled using very-low-radiofrequency power, we used a volume coil for proton decoupling in this study. The homogeneous B1 field of the volume coil was found to significantly enhance the decoupling efficiency of the stochastic decoupling sequence. Detailed specific absorption rates inside the human head were analyzed using the finite difference time domain method to ensure experimental safety. In vivo 13C spectra from the occipital and frontal lobes of the human brain were obtained. At a decoupling power of 30 W (time-averaged power, 2.45 W), the spectra from the occipital lobe showed well-resolved spectral resolution and excellent signal-to-noise ratio. Although frontal lobe 13C spectra were affected by local B0 field inhomogeneity, we demonstrated that the spectral quality could be improved using post-acquisition data processing. In particular, we showed that the frontal lobe glutamine C5 at 178.5 ppm and aspartate C4 at 178.3 ppm could be spectrally resolved with effective proton decoupling and B0 field correction. Because of its large spatial coverage, volume coil decoupling provides the potential to acquire 13C MRS from more than one brain region simultaneously.

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Section: Methodsmentioning

confidence: 99%

¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

Zhang

Wang

et al. 2010

NMR in Biomedicine

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“…At low fields, the Biot‐Savart generates results with reasonable accuracy to the solution of the Maxwell's equations. At high field strengths it is necessary to solve rigorously Maxwell's equations (35). Results of this study also provide confidence to the argument against inaccurate computation of magnetic fields using Maxwell's equation in XFdtd, as reported earlier (19).…”

Section: Discussionmentioning

confidence: 99%

“…This leads to nonoptimal filling factors, and thus nonoptimal B 1 ‐field penetration response for such simulations. Despite the versatility of the employed electromagnetic full‐wave simulation package employed, stringent memory requirements are imposed by full‐wave FDTD electromagnetic modeling calculations that increase exponentially as cell size is reduced, often becoming computationally intensive (35). However, such FDTD calculations are relatively fast and range between 15 and 20 mins on a desktop computer using an Intel processor [Intel(R) Core (TM) Duo CPU], depending on the loading conditions.…”

Section: Discussionmentioning

confidence: 99%

Intercomparison of performance of RF coil geometries for high field mouse cardiac MRI

Constantinides¹,

Angeli²,

Gkagkarellis³

et al. 2011

Concepts Magnetic Resonance

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Multi-turn spiral surface coils are constructed in flat and cylindrical arrangements and used for high field (7.1 T) mouse cardiac MRI. Their electrical and imaging performances, based on experimental measurements, simulations, and MRI experiments in free space, and under phantom, and animal loading conditions, are compared with a commercially available birdcage coil. Results show that the four-turn cylindrical spiral coil exhibits improved relative SNR (rSNR) performance to the flat coil counterpart, and compares fairly well with a commercially available birdcage coil. Phantom experiments indicate a 50% improvement in the SNR for penetration depths ≤ 6.1 mm from the coil surface compared to the birdcage coil, and an increased penetration depth at the half-maximum field response of 8 mm in the 4-spiral cylindrical coil case, in contrast to 2.9 mm in the flat 4-turn spiral case. Quantitative comparison of the performance of the two spiral coil geometries in anterior, lateral, inferior, and septal regions of the murine heart yield maximum mean percentage rSNR increases of the order of 27–167% in vivo post-mortem (cylindrical compared to flat coil). The commercially available birdcage outperforms the cylindrical spiral coil in rSNR by a factor of 3–5 times. The comprehensive approach and methodology adopted to accurately design, simulate, implement, and test radiofrequency coils of any geometry and type, under any loading conditions, can be generalized for any application of high field mouse cardiac MRI.

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“…Here we note that due to the different mesh structures used in the Cartesian and cylindrical coordinate systems, there are some differences between the two conductivity maps, particularly around the periphery of the skull. This leads to some differences in the specific absorption rate (SAR) simulation but has less impact on the magnetic fields, as electric fields can be disturbed more significantly than magnetic fields inside the biological sample [14].…”

Section: Mri Application: Surface Coil-human Head Interactionsmentioning

confidence: 99%

An Improved Cylindrical FDTD Algorithm and Its Application to Field-Tissue Interaction Study in MRI

Chi

Xia

et al. 2011

IEEE Trans. Magn.

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This paper presents a three-dimensional finite-difference time-domain (FDTD) scheme in cylindrical coordinates with an improved algorithm for accommodating the numerical singularity associated with the polar axis. The regularization of this singularity problem is realized based on Faraday's law (for updating the -component) and Ampere's law (for updating the -, -components). The proposed algorithm has been detailed and verified against a problem with a known solution obtained from a commercial electromagnetic simulation package. The numerical scheme is also illustrated by modeling high-frequency RF field-human body interactions in magnetic resonance imaging (MRI). The results demonstrate the accuracy and capability of the proposed algorithm.

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Time-domain finite-difference/finite-element hybrid simulations of radio frequency coils in magnetic resonance imaging

Cited by 13 publications

References 22 publications

¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

Intercomparison of performance of RF coil geometries for high field mouse cardiac MRI

An Improved Cylindrical FDTD Algorithm and Its Application to Field-Tissue Interaction Study in MRI

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Time-domain finite-difference/finite-element hybrid simulations of radio frequency coils in magnetic resonance imaging

Cited by 13 publications

References 22 publications

13C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

13C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

Intercomparison of performance of RF coil geometries for high field mouse cardiac MRI

An Improved Cylindrical FDTD Algorithm and Its Application to Field-Tissue Interaction Study in MRI

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¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling

¹³C MRS of occipital and frontal lobes at 3 T using a volume coil for stochastic proton decoupling