MRI Techniques

Perrin, Vincent

doi:10.1002/9781118761281

Cited by 7 publications

(9 citation statements)

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“…2. The bc faces are conspicuous by absence, being ⊥ B 1 . The resulting MRI tunnel supplies a visual of peering at a virtual absence of EM fields in the interior of a metallic conductor, since the center of the strip is at least (2.25mm/2)/(6.9µm) = 163 skin-depths away from the surface (and hence any EM fields and the MR signal would be virtually buried in noise; see Fig.…”

Section: Mrimentioning

confidence: 99%

“…2a, the signal intensity from the ab faces can be written as (see Eq. (S8)) S ab (x, y) ∝ dx dy dz = dx dy 2δ eff (1) with dx dy dz denoting elemental volume of the metal, and δ eff is the effective subsurface depth that would account for the MR signal in the absence of B 1 decay (see Eq. (S7) and Fig.1).…”

Section: Intensity Ratio Formulae For Bulk Metal Mri and Csimentioning

confidence: 99%

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Visualizing electromagnetic fields in metals by MRI

Chandrashekar¹,

Shellikeri

Chandrashekar

et al. 2017

AIP Advances

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Based upon Maxwell’s equations, it has long been established that oscillating electromagnetic (EM) fields incident upon a metal surface, decay exponentially inside the conductor, leading to a virtual absence of EM fields at sufficient depths. Magnetic resonance imaging (MRI) utilizes radiofrequency (r.f.) EM fields to produce images. Here we present a visualization of a virtual EM vacuum inside a bulk metal strip by MRI, amongst several findings. At its simplest, an MRI image is an intensity map of density variations across voxels (pixels) of identical size (=Δx Δy Δz). By contrast in bulk metal MRI, we uncover that despite uniform density, intensity variations arise from differing effective elemental volumes (voxels) from different parts of the bulk metal. Further, we furnish chemical shift imaging (CSI) results that discriminate different faces (surfaces) of a metal block according to their distinct nuclear magnetic resonance (NMR) chemical shifts, which holds much promise for monitoring surface chemical reactions noninvasively. Bulk metals are ubiquitous, and MRI is a premier noninvasive diagnostic tool. Combining the two, the emerging field of bulk metal MRI can be expected to grow in importance. The findings here may impact further development of bulk metal MRI and CSI.

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Section: Mrimentioning

confidence: 99%

Section: Intensity Ratio Formulae For Bulk Metal Mri and Csimentioning

confidence: 99%

Visualizing electromagnetic fields in metals by MRI

Chandrashekar¹,

Shellikeri

Chandrashekar

et al. 2017

AIP Advances

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“…The simulation accuracy can be guaranteed even with large-size meshes. Besides, the energies of most of the gradient pulses concentrate at low-frequency band, such as GE (gradient echo) and SE (spin echo) [ 7 , 22 , 23 ]. Therefore, the investigation in this work focuses on the frequency band from 100 Hz to 1000 Hz, which can present a more clear observation of the noise reduction scheme effect and the method may still suit the high-frequency condition.…”

Section: Discussionmentioning

confidence: 99%

A Structure Design Method for Reduction of MRI Acoustic Noise

Nan

Zong

Chen

et al. 2017

Computational and Mathematical Methods in Medicine

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The acoustic problem of the split gradient coil is one challenge in a Magnetic Resonance Imaging and Linear Accelerator (MRI-LINAC) system. In this paper, we aimed to develop a scheme to reduce the acoustic noise of the split gradient coil. First, a split gradient assembly with an asymmetric configuration was designed to avoid vibration in same resonant modes for the two assembly cylinders. Next, the outer ends of the split main magnet were constructed using horn structures, which can distribute the acoustic field away from patient region. Finally, a finite element method (FEM) was used to quantitatively evaluate the effectiveness of the above acoustic noise reduction scheme. Simulation results found that the noise could be maximally reduced by 6.9 dB and 5.6 dB inside and outside the central gap of the split MRI system, respectively, by increasing the length of one gradient assembly cylinder by 20 cm. The optimized horn length was observed to be 55 cm, which could reduce noise by up to 7.4 dB and 5.4 dB inside and outside the central gap, respectively. The proposed design could effectively reduce the acoustic noise without any influence on the application of other noise reduction methods.

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“…MRI is a household name as a diagnostic tool in the medical field, 10,11 with an impressive resume in many other fields, including the study of materials, [12][13][14][15] corrosion of metals, monitoring batteries and supercapacitors. 16,17 However, historically, MRI of bulk metals has been very rare, limited to specialized cells using r.f.…”

Section: Introductionmentioning

confidence: 99%

Visualizing Electromagnetic Vacuum by MRI

Chandrashekar¹,

Shellikeri²,

S.³

et al. 2016

Preprint

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Based upon Maxwell's equations, it has long been established that oscillating electromagnetic (EM) fields incident upon a metal surface decay exponentially inside the conductor, 1-3 leading to a virtual EM vacuum at sufficient depths. Magnetic resonance imaging (MRI) utilizes radiofrequency (r.f.) EM fields to produce images. Here we present the first visualization of a virtual EM vacuum inside a bulk metal strip by MRI, amongst several novel findings.We uncover unexpected MRI intensity patterns arising from two orthogonal pairs of faces of a metal strip, and derive formulae for their intensity ratios, revealing differing effective elemental volumes (voxels) underneath these faces.Further, we furnish chemical shift imaging (CSI) results that discriminate different faces (surfaces) of a metal block according to their distinct nuclear magnetic resonance (NMR) chemical shifts, which holds much promise for monitoring surface chemical reactions noninvasively.Bulk metals are ubiquitous, and MRI is a premier noninvasive diagnostic tool. Combining the two, the emerging field of bulk metal MRI can be expected to grow in importance. The fundamental nature of results presented here may impact bulk metal MRI and CSI across many fields. arXiv:1610.03710v3 [cond-mat.mtrl-sci]

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MRI Techniques

Cited by 7 publications

References 0 publications

Visualizing electromagnetic fields in metals by MRI

Visualizing electromagnetic fields in metals by MRI

A Structure Design Method for Reduction of MRI Acoustic Noise

Visualizing Electromagnetic Vacuum by MRI

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