Theory of the spin echo signal in NMR microscopy: analytic solutions of a generalized Torrey–Bloch equation

SUMMARY Surface nuclear magnetic resonance (NMR) measurements show great promise for characterization of subsurface water content, pore-sizes and permeability. The link between surface NMR and pore-size/permeability is founded in the connection between the NMR signal's time dependence and the geometry of the pore-space. To strengthen links between the NMR signal and pore-geometry multipulse surface NMR sequences have been developed to estimate the parameter T2, which carries a strong link to pore-geometry and has formed the basis for NMR-based permeability estimation in the petroleum industry for decades. Producing reliable subsurface characterizations from multipulse surface NMR measurements that measure T2 requires that the forward model is able to accurately predict the transverse magnetization at the time when the measurement occurs. Traditional surface NMR T2 forward models employ an analytic expression for the transverse magnetization, an expression developed in the context of laboratory NMR experiments conducted under conditions significantly different from surface NMR and which require several assumptions to simplify the underlying Bloch equation. To investigate the reliability of this analytic expression under surface NMR conditions, a synthetic comparison is performed where the analytic expression is contrasted against the transverse magnetization predicted from a solution of the full-Bloch equation without the same simplifying assumptions and which can appropriately weight heterogeneity in the applied and background magnetic fields. The comparison shows that the analytic expression breaks down in a range of conditions typical to surface NMR measurements.

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The effect of a pulsed magnetic field on the nuclear spin echo signal in ferrite

Technical Physics Letters ◽

10.1134/s1063785012090246 ◽

2012 ◽

Vol 38 (9) ◽

pp. 853-855 ◽

Cited By ~ 6

Author(s):

I. V. Pleshakov ◽

N. S. Klekhta ◽

Yu. I. Kuz’min

Keyword(s):

Magnetic Field ◽

Nuclear Spin ◽

Spin Echo ◽

Pulsed Magnetic Field ◽

Echo Signal

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Obtaining a spin echo-signal from a magnetic liquid in a homogeneous external field

Russian Physics Journal ◽

10.1007/s11182-005-0026-0 ◽

2004 ◽

Vol 47 (10) ◽

pp. 1085-1086

Author(s):

A. I. Zhernovoi ◽

M. N. Nikolaeva

Keyword(s):

External Field ◽

Spin Echo ◽

Echo Signal ◽

Magnetic Liquid

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Amplitude and Phase of Spin-Echo Signals in Bulk Metals

Zeitschrift für Naturforschung A ◽

10.1515/zna-1973-1007 ◽

1973 ◽

Vol 28 (10) ◽

pp. 1607-1612 ◽

Cited By ~ 12

Author(s):

D. Kotzur ◽

M. Mehring ◽

O. Kanert

Keyword(s):

Sample Size ◽

Pulse Sequence ◽

Spin Echo ◽

Skin Depth ◽

Sample Thickness ◽

Echo Signal ◽

Metallic Material ◽

Copper Foils ◽

Optimal Values ◽

Theoretical Results

The amplitude and phase of the spin echo signal in bulk metallic material after a -β10-τ-β20 (α) pulse sequence has been calculated in the case of spin I=3/2, 5/2, 7/2, 9/2, for different ratios of the sample thickness to the skin depth. Optimal values for β10, β20 and a are obtained in the sense that the echo signal is maximized. These optimal values depend again on the spin I and the relative sample size. The theoretical results compare reasonably well with experiments, performed on 63Cu in copper foils of different size.

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GRE T2*-Weighted MRI: Principles and Clinical Applications

BioMed Research International ◽

10.1155/2014/312142 ◽

2014 ◽

Vol 2014 ◽

pp. 1-12 ◽

Cited By ~ 17

Author(s):

Meng Yue Tang ◽

Tian Wu Chen ◽

Xiao Ming Zhang ◽

Xiao Hua Huang

Keyword(s):

Magnetic Field ◽

Spin Echo ◽

Clinical Applications ◽

Lesion Detection ◽

Small Lesion ◽

Echo Signal ◽

Advantages And Disadvantages ◽

High Uniformity ◽

Magnetic Resonance Imaging Mri ◽

The Magnetic Field

The sequence of a multiecho gradient recalled echo (GRE) T2*-weighted imaging (T2*WI) is a relatively new magnetic resonance imaging (MRI) technique. In contrast to T2 relaxation, which acquires a spin echo signal, T2*relaxation acquires a gradient echo signal. The sequence of a GRE T2*WI requires high uniformity of the magnetic field. GRE T2*WI can detect the smallest changes in uniformity in the magnetic field and can improve the rate of small lesion detection. In addition, the T2*value can indirectly reflect changes in tissue biochemical components. Moreover, it can be used for the early diagnosis and quantitative diagnosis of some diseases. This paper reviews the principles and clinical applications as well as the advantages and disadvantages of GRE T2*WI.

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