Effect of Three-Spin Groups on the Decay of Free Induction and the Primary Spin Echo in Linear Polymers with Free Ends

2021 ◽  
Vol 85 (8) ◽  
pp. 894-897
Author(s):  
T. P. Kulagina ◽  
G. E. Karnaukh ◽  
I. Yu. Golubeva
Keyword(s):  
Spin Echo ◽  
Linear Polymers ◽  
Spin Groups ◽  
Free Induction

Advancement and validation of surface nuclear magnetic resonance spin-echo measurements of T2

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. EN15-EN23 ◽  
Author(s):  
Elliot Grunewald ◽  
Rosemary Knight ◽  
David Walsh
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pore Size ◽  
Free Induction Decay ◽  
Field Experiments ◽  
Spin Echo ◽  
Coarse Grained ◽  
Background Magnetic Field ◽  
Free Induction ◽  
Nuclear Magnetic

Obtaining reliable estimates of hydrogeologic properties from nuclear magnetic resonance (NMR) measurements requires the ability to measure NMR relaxation parameters that are most sensitive to pore-scale geometry. Conventional surface NMR measurements of the free induction decay yield accurate estimates of the relaxation time parameter [Formula: see text], but it has been shown that this parameter can exhibit limited sensitivity to pore size and permeability. We evaluated an improved surface-NMR scheme that uses spin-echo signals to estimate the more robust and readily usable relaxation parameter [Formula: see text]. The acquisition methodology builds upon previous spin-echo schemes and incorporates robust phase-cycling procedures, which remove responses that can potentially interfere with the echo signals. A new two-stage linear inversion was used to derive quantitative estimates of [Formula: see text] with depth. The method was evaluated in two field experiments at sites in the central and western United States. At one site, NMR logging measurements in a nearby borehole provided the first opportunity to compare [Formula: see text]-values estimated by surface NMR to [Formula: see text]-values determined from the logging data. The surface and logging results showed very close agreement at depths where [Formula: see text] is long, but echoes cannot be detected from depths where [Formula: see text] is shorter than the minimum echo time. As anticipated, we found that [Formula: see text] derived from spin echoes was generally much longer than [Formula: see text], derived from the free induction decay. We explain the observed differences by considering the magnitude of inhomogeneity in the background magnetic field. We note that [Formula: see text] exhibited greater variation and sensitivity to pore size than [Formula: see text] in coarse-grained materials, while [Formula: see text] provided greater sensitivity in fine-grained materials where no echo signal was detected. Given these complementary advantages of [Formula: see text] and [Formula: see text] measurement, we advocate adoption of a framework combining spin-echo and free induction decay data to improve characterization of groundwater aquifers.

Influence of Three-Spin Groups on the Primary Echo in Linear Polymers with Free Ends

2021 ◽  
Vol 15 (5) ◽  
pp. 772-776
Author(s):  
T. P. Kulagina ◽  
G. E. Karnaukh ◽  
I. Yu. Golubeva
Keyword(s):  
Linear Polymers ◽  
Spin Groups

Peculiarities of free induction and primary spin echo signals for spin-correlated radical pairs

1992 ◽  
Vol 3 (1) ◽  
pp. 199-216 ◽  
Author(s):  
K. M. Salikhov ◽  
Yu. E. Kandrashkin ◽  
A. K. Salikhov
Keyword(s):  
Spin Echo ◽  
Radical Pairs ◽  
Free Induction

FID-calibrated simultaneous multi-slice fast spin echo with long trains of hard pulses

2022 ◽  
Author(s):  
Eun Ji Lim ◽  
Chul-Ho Sohn ◽  
Taehoon Shin ◽  
Jaeseok Park
Keyword(s):  
Energy Deposition ◽  
Spin Echo ◽  
Correction Method ◽  
Fast Spin Echo ◽  
Single Shot ◽  
Apparent Loss ◽  
Free Induction ◽  
Efficient Alternative ◽  
Encoding Efficiency ◽  
Fast Spin

Abstract Objective: To develop a novel, free-induction-decay (FID)-calibrated single-shot simultaneous multi-slice fast spin echo (SMS-FSE) with very long hard pulse trains for high encoding efficiency and low energy deposition. Approach: The proposed single-shot SMS-FSE employs a mixed pulse configuration in which a long excitation pulse that is spatially multi-band (MB) selective is used in conjunction with short spatially nonselective refocusing pulses. To alleviate energy deposition to tissues while reducing signal modulation along the echo train, variable low flip angles with signal prescription are utilized in the refocusing pulse train. A time-efficient FID-calibration and correction method is introduced before aliased voxels in the slice direction are resolved. Simulations and experiments are performed to demonstrate the feasibility of the proposed method as an alternative to conventional HASTE for generating T2-weighted images. Main results: Compared with conventional HASTE, the proposed method enhances imaging speed effectively by an MB factor up to 5 without apparent loss of image contrast while successfully eliminating FID artifacts. Significance: We successfully demonstrated the feasibility of the proposed method as an encoding- and energy-efficient alternative to conventional HASTE for generation of T2-weighted contrast.

Alveolar air-tissue interface and nuclear magnetic resonance behavior of lung

1991 ◽  
Vol 70 (5) ◽  
pp. 2145-2154 ◽  
Author(s):  
A. G. Cutillo ◽  
K. Ganesan ◽  
D. C. Ailion ◽  
A. H. Morris ◽  
C. H. Durney ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Spin Echo ◽  
Lung Water ◽  
Alveolar Air ◽  
Resonance Behavior ◽  
Theoretical Predictions ◽  
Free Induction ◽  
Tissue Interface ◽  
Nuclear Magnetic

Inflated lungs are characterized by a short nuclear magnetic resonance (NMR) free induction decay (rapid disappearance of NMR signal), likely due to internal (tissue-induced) magnetic field inhomogeneity produced by the alveolar air-tissue interface. This phenomenon can also be detected using temporally symmetric and asymmetric NMR spin-echo sequences; these sequences generate a pair of NMR images from which a difference signal (delta) is obtained (reflecting the signal from lung water experiencing the air-tissue interface effect). We measured delta in normal excised rat lungs at inflation pressures of 0-30 cmH2O for asymmetry times (a) of 1-6 ms. Delta was low in degassed lungs and increased markedly with alveolar opening when measured at a = 6 ms (delta 6 ms); delta 6 ms varied little during the rest of the inflation-deflation cycle. Delta 1 ms (a = 1 ms) did not vary significantly on inflation and deflation. Measurements of delta at a = 3 and 5 ms generally lay between those of delta 1 ms and delta 6 ms. These findings, which are consistent with theoretical predictions, suggest that measurements of delta at appropriate asymmetry times are particularly sensitive to alveolar opening and may provide a means of distinguishing alveolar recruitment from alveolar distension in the pressure-volume behavior of the lung.

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