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Contributions of chemical and diffusive exchange to T dispersion

Authors

  • Jared Guthrie Cobb,

    Corresponding author
    1. Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
    2. Department of Radiology and Radiological Sciences, Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA
    • Ph.D., Vanderbilt University Institute of Imaging Science, AA 3112 MCN, 1161 21st Avenue South, Nashville, TN 37232-2310
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  • Jingping Xie,

    1. Department of Radiology and Radiological Sciences, Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA
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  • John C. Gore

    1. Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
    2. Department of Radiology and Radiological Sciences, Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA
    3. Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA
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Abstract

Variations in local magnetic susceptibility may induce magnetic field gradients that affect the signals acquired for MR imaging. Under appropriate diffusion conditions, such fields produce effects similar to slow chemical exchange. These effects may also be found in combination with other chemical exchange processes at multiple time scales. We investigate these effects with simulations and measurements to determine their contributions to rotating frame (R) relaxation in model systems. Simulations of diffusive and chemical exchange effects on R dispersion were performed using the Bloch equations. Additionally, R dispersion was measured in suspensions of Sephadex and latex beads with varying spin locking fields at 9.4 T. A novel analysis method was used to iteratively fit for apparent chemical and diffusive exchange rates with a model by Chopra et al. Single- and double-inflection points in R dispersion profiles were observed, respectively, in simulations of slow diffusive exchange alone and when combined with rapid chemical exchange. These simulations were consistent with measurements of R in latex bead suspensions and small-diameter Sephadex beads that showed single- and double-inflection points, respectively. These observations, along with measurements following changes in temperature and pH, are consistent with the combined effects of slow diffusion and rapid OH exchange processes. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

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