A cumulant analysis for non-Gaussian displacement distributions in Newtonian and non-Newtonian flows through porous media

Scheven, Ulrich M.; Crawshaw, John; Anderson, Valerie J.; Harris, R.J.; Johns, Michael L.; Gladden, Lynn F.

doi:10.1016/j.mri.2006.11.020

Cited by 14 publications

(4 citation statements)

References 3 publications

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“…In porous media, the presence of stagnating or differential flow clearly produces strongly asymmetric intravoxel displacements [26]. Scheven et al [36] used a cumulant analysis of small |q| PFG data to extract the displacement distribution moments for Newtonian and non-Newtonian fluid flowing through a beadpack. More recently, we were able to reproduce experimental phase measurement errors using simulations based on experimental propagator data obtained in sandstone rock flow, showing that important PCV errors can be quantitatively related to the shape of the intravoxel displacement distribution [37].…”

Section: Introductionmentioning

confidence: 99%

Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions

Vallatos

Al-Mubarak

Mullin

et al. 2018

Journal of Magnetic Resonance

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Phase contrast velocimetry (PCV) has been widely used to investigate flow properties in numerous systems. Several authors have reported errors in velocity measurements and have speculated on the sources, which have ranged from eddy current effects to acceleration artefacts. An often overlooked assumption in the theory of PCV, which may not be met in complex or unsteady flows, is that the intravoxel displacement distributions (propagators) are symmetric. Here, the effect of the higher moments of the displacement distribution (variance, skewness and kurtosis) on the accuracy of PCV is investigated experimentally and theoretically. Phase and propagator measurements are performed on tailored intravoxel distributions, achieved using a simple phantom combined with a single large voxel. Asymmetric distributions (Skewness ≠ 0) are shown to generate important phase measurement errors that lead to significant velocimetry errors. Simulations of the phase of the spin vector sum, based on experimentally measured propagators, are shown to quantitatively reproduce the relationship between measured phase and experimental parameters. These allow relating the observed velocimetry errors to a discrepancy between the average phase of intravoxel spins considered in PCV theory and the vector phase actually measured by a PFG experiment. A theoretical expression is derived for PCV velocimetry errors as a function of the moments of the displacement distribution. Positively skewed distributions result in an underestimation of the true mean velocity, while negatively skewed distributions result in an overestimation. The magnitude of these errors is shown to increase with the variance and decrease with the kurtosis of the intravoxel displacement distribution.

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Section: Introductionmentioning

confidence: 99%

Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions

Vallatos

Al-Mubarak

Mullin

et al. 2018

Journal of Magnetic Resonance

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“…We deemed use of the propagator mode the best analysis for control of uncertainty in our velocity maps. However, these low resolution measurements may very well benefit from optimisation with a cumulant analysis [24].…”

Section: Potential Improvements To the Measurementmentioning

confidence: 99%

SPRITE MRI of bubbly flow in a horizontal pipe

Sankey

Yang

Gladden

et al. 2009

Journal of Magnetic Resonance

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“…The results from these experiments were analyzed by pore‐scale network modeling incorporating the non‐Newtonian fluid mechanics of a Carreau fluid. Wang et al156 carried out experimental work on dead oils obtained from four wells in the Chinese Zaoyuan oilfield by injecting oil into sand pack cores. The investigation included yield‐stress, viscoelastic and thixotropic aspects using Herschel‐Bulkley model. Schevena et al168 conducted experimental research on Newtonian and non‐Newtonian flows through rocks and bead packs. The experiments involved the use of shear‐thinning Xanthan solutions and packed beds of near‐monodisperse Ballotini beads.…”

Section: Experimental Work On Non‐newtonian Flow In Porous Mediamentioning

confidence: 99%

“…Schevena et al168 conducted experimental research on Newtonian and non‐Newtonian flows through rocks and bead packs. The experiments involved the use of shear‐thinning Xanthan solutions and packed beds of near‐monodisperse Ballotini beads.…”

Section: Experimental Work On Non‐newtonian Flow In Porous Mediamentioning

confidence: 99%

The conundrum of migraine headaches in the presence of patent foramen ovale

Tobis

2009

Cathet Cardio Intervent

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The accompanying article by the interventional group in Geneva describes their experience in 17 patients who had their PFO closed solely for the indication of severe migraine headaches. This is distinct from most prior observational studies that describe the effect on migraine headache of PFO closure when the procedure was performed primarily to prevent recurrent stroke or decompression illness. Approximately 70% of the patients in this study had a significant decrease or complete abolition (in 24% of cases) of migraine headaches. This current report supplements a recent report by Vigna et al., which describes a positive experience with PFO closure in 53 patients who had migraine headaches and white matter lesions [1]. In that study, the mean number of migraine attacks decreased from 32 to 7 over a 6-month follow up period in the patients who had PFO closure, compared to no significant change in the patients who chose not to have their PFO closed.The observational data obtained from these recent reports, in conjunction with prior observations in cryptogenic stroke patients, is very consistent. Unfortunately, the only randomized controlled trial to date evaluating the effectiveness of PFO closure for migraine headache treatment, the MIST Trial, did not show significant improvement. However, it is believed that a significant proportion of patients in the MIST Trial had a residual shunt after device insertion, likely due to inadequate closure provided by the Starflex device. In addition, the characteristics of the patient population may be different between those included in the MIST Trial and the observational reports, including the present one from Geneva. I hope neurologists consider all the evidence that is currently available and maintain an open position with respect to the association of migraine headaches and patent foramen ovale.There are multiple questions that remain concerning PFO closure and migraine. For instance, we still have not identified which characteristics predict the patients likely to respond to PFO closure. Will the responders include only those with visual aura? Approximately 75% of patients with migraine with aura have a significant benefit from PFO closure, but we have seen about 30% of the patients with migraine without aura who also responded to PFO closure [2]. Are the responders more likely to have transient neurologic deficits (which are frequently misdiagnosed as transient ischemic attacks but actually are complex migraine)? Or should we be concentrating on the patient population that already has evidence of brain involvement; that is, those people with white matter lesions on MRI?Although the majority (60%) of patients screened in the MIST trial had a right to left shunt, there clearly are many people with migraine who do not have a PFO or other etiology of a right to left shunt. In addition, not everyone with a PFO and migraines responds to PFO closure. Nevertheless, as physicians, we are struck by the enormous amount of suffering that patients with frequent migraine must endure. ...

show abstract

A cumulant analysis for non-Gaussian displacement distributions in Newtonian and non-Newtonian flows through porous media

Cited by 14 publications

References 3 publications

Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions

Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions

SPRITE MRI of bubbly flow in a horizontal pipe

The conundrum of migraine headaches in the presence of patent foramen ovale

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