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Contributions of chemical exchange to T1ρ dispersion in a tissue model.

Cobb JG, Xie J, Gore JC
Magn Reson Med. 2011 66 (6): 1563-71

PMID: 21590720 · PMCID: PMC4521630 · DOI:10.1002/mrm.22947

Variations in T(1ρ) with locking-field strength (T(1ρ) dispersion) may be used to estimate proton exchange rates. We developed a novel approach utilizing the second derivative of the dispersion curve to measure exchange in a model system of cross-linked polyacrylamide gels. These gels were varied in relative composition of comonomers, increasing stiffness, and in pH, modifying exchange rates. Magnetic resonance images were recorded with a spin-locking sequence as described by Sepponen et al. These measurements were fit to a mono-exponential decay function yielding values for T(1ρ) at each locking-field measured. These values were then fit to a model by Chopra et al. for estimating exchange rates. For low stiffness gels, the calculated exchange values increased by a factor of 4 as pH increased, consistent with chemical exchange being the dominant contributor to T(1ρ) dispersion. Interestingly, calculated chemical exchange rates also increased with stiffness, likely due to modified side-chain exchange kinetics as the composition varied. This article demonstrates a new method to assess the structural and chemical effects on T(1ρ) relaxation dispersion with a suitable model. These phenomena may be exploited in an imaging context to emphasize the presence of nuclei of specific exchange rates, rather than chemical shifts.

Copyright © 2011 Wiley Periodicals, Inc.

MeSH Terms (10)

Algorithms Computer Simulation Image Enhancement Image Interpretation, Computer-Assisted Magnetic Resonance Imaging Models, Biological Phantoms, Imaging Protons Reproducibility of Results Sensitivity and Specificity

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