TY - JOUR

T1 - Suppressing magnetization exchange effects in stimulated-echo diffusion experiments

AU - Pagès, Guilhem

AU - Dvinskikh, Sergey V.

AU - Furó, István

PY - 2013/1/1

Y1 - 2013/1/1

N2 - Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T2 difference between the different spin pools.

AB - Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T2 difference between the different spin pools.

KW - Agarose

KW - Chemical exchange

KW - Cross-relaxation

KW - Diffusion measurements

KW - PGSTE NMR

KW - Pulsed-field-gradient stimulated-echo NMR

KW - Water

UR - http://www.scopus.com/inward/record.url?scp=84880182663&partnerID=8YFLogxK

U2 - 10.1016/j.jmr.2013.06.001

DO - 10.1016/j.jmr.2013.06.001

M3 - Article

AN - SCOPUS:84880182663

VL - 234

SP - 35

EP - 43

JO - Journal of Magnetic Resonance - Series A

JF - Journal of Magnetic Resonance - Series A

SN - 1090-7807

ER -