Conditions for initial quasilinear<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">T</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mi mathvariant="normal">−</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:mrow></mml:math>versus τ for Carr-Purcell-Meiboom-Gill NMR with diffusion and susceptibility differences in porous media and tissues

Brown, R. James; Fantazzini, Paola

doi:10.1103/physrevb.47.14823

Cited by 96 publications

(72 citation statements)

References 19 publications

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“…When we fitted Eqs. [10], [12], [15], and [16] in Microcal Origin, on average, the simulation data conformed to theory within a constant scaling factor of 6.67 Ϯ 0.44 when B 0 ⅐ ⌬ Ͻ 5 T. In addition, as expected from theory, we found the R* 2 Ͼ R 2 and the * Ͼ independent of the choice of parameters.…”

Section: Simulation Resultssupporting

confidence: 80%

“…In addition, if the field variations are weak, it is possible to approximate Eq. [5] with the second moment as a function of time (15,16). In this case, Eq.…”

Section: Parameters Affecting the Rate Of Decay Of The Mr Signalmentioning

confidence: 99%

“…Equations [10], [12], [15], and [16] imply that the R* 2 , R 2 , *, and are linearly related to , but quadratically related to B 0 and ⌬ . When R 0 , , ⌬ , and B 0 remain fixed, the theory also predicts that R 2 and will initially increase with increase in 180 and then reach a plateau.…”

Section: Relation Between R* 2 and Pressurementioning

confidence: 99%

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On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Dharmakumar

Plewes

Wright

2002

Magnetic Resonance in Med

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Recently, it has been suggested that gas encapsulated distensible microbubbles may serve as pressure probes in the MR field through the relationship between bubble size and 1/T 2 or 1/T* 2 . Currently, in vivo application of this technique is hindered by the ability of T 2 or T * 2 to detect pressure changes that are clinically relevant. This work identifies and characterizes, through numerical simulations, the set of parameters which optimize the ability of this technique to detect small pressure changes. Results show that when the bubbles do not interact magnetically, the T 2 -and T * 2 -based measurements of pressure are strongly influenced by the bubble size at atmospheric pressure, static magnetic field strength, magnitude of the susceptibility difference between the encapsulated gas and plasma, bubble volume fraction, and the refocusing interval.

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Section: Simulation Resultssupporting

confidence: 80%

“…In addition, if the field variations are weak, it is possible to approximate Eq. [5] with the second moment as a function of time (15,16). In this case, Eq.…”

Section: Parameters Affecting the Rate Of Decay Of The Mr Signalmentioning

confidence: 99%

See 1 more Smart Citation

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Dharmakumar

Plewes

Wright

2002

Magnetic Resonance in Med

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“…This expression can include a third term, to account for the effect of internal field gradients (G) on the diffusing hydrogen nuclei [Brown and Fantazinni, 1993]. However, in this study we found experimentally that G was negligible, so (4) describes the NMR response of our samples.…”

Section: Nmr Relaxationmentioning

confidence: 56%

Geochemical Controls on Nuclear Magnetic Resonance Measurements

Knight¹

2008

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Proton nuclear magnetic resonance (NMR) is used in the Earth Sciences as a means of obtaining information about the molecular-scale environment of fluids in porous geological materials. Laboratory experiments were conducted to advance our fundamental understanding of the link between the NMR response and the geochemical properties of geological materials. In the first part of this research project, we studied the impact of both the surface-area-to-volume ratio (S/V) of the pore space and the surface relaxivity on the NMR response of fluids in sandclay mixtures. This study highlighted the way in which these two parameters control our ability to use NMR measurements to detect and quantify fluid saturation in multiphase saturated systems. The second part of the project was designed to explore the way in which the mineralogic form of iron, as opposed to simply the concentration of iron, affects the surface relaxation rate and, more generally, the NMR response of porous materials. We found that the magnitude of the surface relaxation rate was different for the various iron-oxide minerals because of changes in both the surface-area-to-volume ratio of the pore space, and the surface relaxivity. Of particular significance from this study was the finding of an anomalously large surface relaxivity of magnetite compared to that of the other iron minerals. Differences in the NMR response of iron minerals were seen in column experiments during the reaction of ferrihydrite-coated quartz sand with aqueous Fe(II) solutions to form goethite, lepidocrocite and magnetite; indicating the potential use of NMR as a means of monitoring geochemical reactions. The final part of the research project investigated the impact of heterogeneity, at the pore-scale, on the NMR response. This work highlighted the way in which the geochemistry, by controlling the surface relaxivity, has a significant impact on the link between NMR data and the microgeometry of the pore space. Introduction and Research ObjectivesNuclear magnetic resonance (NMR) is a measurement technique, developed in the 1940's, that can provide an incredible amount of information about molecular-scale processes and properties in a wide range of materials. Of specific interest in our research is proton NMR, which investigates the molecular-scale environment of hydrogen nuclei. In the Earth sciences proton NMR is most commonly used to measure the response of water in porous geological materials, as a way of obtaining information about the water content and microgeometry of the water-filled regions of the pore space. Despite many years of the use and study of NMR for borehole logging in the petroleum industry there still remain key questions about the basic mechanisms governing NMR relaxation measurements. As a result, the potential of NMR as a means of determining and studying the physical, chemical and biological properties of Earth materials is far from being fully realized. 2The goal of our research was to advance the fundamental understanding of the link between the NM...

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“…Given the inhomogeneous nature of the electronic texture [33,34], an internal magnetic field gradient ∇B could originate from a spatial inhomogeneity of the spin susceptibility χ or, equivalently, of the local magnetization χ H [35,36]. Hence, ∇B χ H/2a, where 2a defines a typical domain size [35].…”

Section: Discussionmentioning

confidence: 99%

Persistence of slow fluctuations in the overdoped regime of Ba(Fe1-xRhx)2As2 superconductors

Bossoni

Moroni

Julien

et al. 2016

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We present nuclear magnetic resonance evidence that very slow ( 1 MHz) spin fluctuations persist into the overdoped regime of Ba(Fe 1−x Rh x ) 2 As 2 superconductors. Measurements of the 75 As spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating (π/a,0) from (0,π/a) correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.

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Conditions for initial quasilinearT2−1versus τ for Carr-Purcell-Meiboom-Gill NMR with diffusion and susceptibility differences in porous media and tissues

Cited by 96 publications

References 19 publications

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Geochemical Controls on Nuclear Magnetic Resonance Measurements

Persistence of slow fluctuations in the overdoped regime of Ba(Fe<sub>1-x</sub>Rh<sub>x</sub>)<sub>2</sub>As<sub>2</sub> superconductors

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