B1 mapping with a pure phase encode approach: Quantitative density profiling

Vashaee, Sarah; Newling, Benedict; MacMillan, Bryce; Balcom, Bruce J.

doi:10.1016/j.jmr.2013.04.012

Cited by 15 publications

(9 citation statements)

References 46 publications

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“…The RF probe employed for the measurements was a birdcage probe. B 1 field mapping experiments were carried out by Vashaee et al to calculate the spatial B 1 field distribution for this RF probe. The B 1 field varies spatially with the greatest strength at the edges and decreasing strength toward the center for a birdcage probe.…”

Section: Resultsmentioning

confidence: 99%

Systematic image alteration due to phase accumulation during RF pulse excitation in pure phase encode magnetic resonance imaging

McDonald

MacMillan

Newling

et al. 2016

Concepts Magnetic Resonance

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The SPI/SPRITE class of techniques in magnetic resonance imaging are pure phase encode methods that are well established for systems with short transverse signal lifetimes. Applying a broadband radio-frequency pulse in the presence of a magnetic field gradient is unconventional in MRI but fundamental to these methods. Ordinarily, it is assumed that the excitation is instantaneous and any possible phase evolution during the RF pulse is ignored. High quality, quantitative imaging of a variety of samples over many years suggests that the off-resonance effects of the RF pulse, with consequent phase accumulation during the pulse, are not significant. However, a reconsideration of the RF pulse behavior in related work has shown that phase accumulation during the pulse may be non-negligible in some circumstances.The effect of phase accumulation during the RF pulse is investigated through simulation of one-dimensional SPI experiments and is shown to manifest as a systematic scaling of the image field-of-view (FOV). The FOV scaling effect is also verified experimentally. One-dimensional profiles of a cylindrical elastomer sample were acquired employing a 2.4 T horizontal bore magnet. Experiments were undertaken with variation of the experimental RF pulse duration. Under typical experimental parameters, neglecting the phase accumulation during the RF pulse is acceptable.

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Section: Resultsmentioning

confidence: 99%

Systematic image alteration due to phase accumulation during RF pulse excitation in pure phase encode magnetic resonance imaging

McDonald

MacMillan

Newling

et al. 2016

Concepts Magnetic Resonance

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“…We also analytically measure the local B 1 field in the sample space with a recently introduced B 1 mapping method [41]. The SPRITE MRI signal in each pixel (or voxel) is proportional to B 1 2 due to B 1 sensitivity in both excitation and reception.…”

Section: Introductionmentioning

confidence: 99%

“…The SPRITE MRI signal in each pixel (or voxel) is proportional to B 1 2 due to B 1 sensitivity in both excitation and reception. Therefore, the method is very sensitive to B 1 variation in the sample space [41].…”

Section: Introductionmentioning

confidence: 99%

Mapping B1-induced eddy current effects near metallic structures in MR images: A comparison of simulation and experiment

Vashaee

Goora

Britton

et al. 2015

Journal of Magnetic Resonance

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Magnetic resonance imaging (MRI) in the presence of metallic structures is very common in medical and non-medical fields. Metallic structures cause MRI image distortions by three mechanisms: (1) static field distortion through magnetic susceptibility mismatch, (2) eddy currents induced by switched magnetic field gradients and (3) radio frequency (RF) induced eddy currents. Single point ramped imaging with T1 enhancement (SPRITE) MRI measurements are largely immune to susceptibility and gradient induced eddy current artifacts. As a result, one can isolate the effects of metal objects on the RF field. The RF field affects both the excitation and detection of the magnetic resonance (MR) signal. This is challenging with conventional MRI methods, which cannot readily separate the three effects. RF induced MRI artifacts were investigated experimentally at 2.4 T by analyzing image distortions surrounding two geometrically identical metallic strips of aluminum and lead. The strips were immersed in agar gel doped with contrast agent and imaged employing the conical SPRITE sequence. B1 mapping with pure phase encode SPRITE was employed to measure the B1 field around the strips of metal. The strip geometry was chosen to mimic metal electrodes employed in electrochemistry studies. Simulations are employed to investigate the RF field induced eddy currents in the two metallic strips. The RF simulation results are in good agreement with experimental results. Experimental and simulation results show that the metal has a pronounced effect on the B1 distribution and B1 amplitude in the surrounding space. The electrical conductivity of the metal has a minimal effect.

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“…These artifacts occur for several reasons, notably susceptibility differences with surrounding material causing additional magnetic field gradients, 2 eddy currents due to RF or magnetic field gradient switching 4 and RF inhomogeneity. 11 For the same reasons, MRI measurements of electrochemical processes where a metallic component is present, such as the zinc anode in a Zn-air battery, is not a trivial matter. However, we have found that optimization of the orientation of the zinc electrode with respect to the radio frequency (r.f.)…”

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confidence: 99%

“…We believe the artifacts due to a variation in the strength of the r.f. field, 11 which locally modulates the signal around the metal, causing image distortions.…”

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confidence: 99%

In Situ, Real-Time Visualization of Electrochemistry Using Magnetic Resonance Imaging

Britton

Bayley

Howlett

et al. 2013

J. Phys. Chem. Lett.

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The drive to develop better electrochemical energy storage devices requires the development of not only new materials, but also better understanding of the underpinning chemical and dynamical processes within such devices during operation, for which new analytical techniques are required. Currently, there are few techniques that can probe local composition and transport in the electrolyte during battery operation. In this paper, we report a novel application of magnetic resonance imaging (MRI) for probing electrochemical processes in a model electrochemical cell. Using MRI, the transport and zinc and oxygen electrochemistry in an alkaline electrolyte, typical of that found in zinc-air batteries, are investigated. Magnetic resonance relaxation maps of the electrolyte are used to visualize the chemical composition and electrochemical processes occurring during discharge in this model metal-air battery. Such experiments will be useful in the development of new energy storage/conversion devices, as well as other electrochemical technologies.

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B1 mapping with a pure phase encode approach: Quantitative density profiling

Cited by 15 publications

References 46 publications

Systematic image alteration due to phase accumulation during RF pulse excitation in pure phase encode magnetic resonance imaging

Systematic image alteration due to phase accumulation during RF pulse excitation in pure phase encode magnetic resonance imaging

Mapping B1-induced eddy current effects near metallic structures in MR images: A comparison of simulation and experiment

In Situ, Real-Time Visualization of Electrochemistry Using Magnetic Resonance Imaging

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