In vivo imaging of paraCEST agents using frequency labeled exchange transfer MRI

Authors

  • Chien-Yuan Lin,

    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
    2. F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
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  • Nirbhay N. Yadav,

    1. F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
    2. Division of MR Research, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA
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  • James Ratnakar,

    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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  • A. Dean Sherry,

    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
    2. Depatment of Chemistry, University of Texas at Dallas, Dallas, Texas, USA
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  • Peter C. M. van Zijl

    Corresponding author
    1. F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
    2. Division of MR Research, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA
    • Correspondence to: Peter C. M. van Zijl, Ph.D., Department of Radiology, Johns Hopkins University School of Medicine, 217 Traylor Bldg, 720 Rutland Ave, Baltimore, MD 21205, USA. E-mail: pvanzijl@mri.jhu.edu

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Abstract

Purpose

A main obstacle to in vivo applications of paramagnetic chemical exchange saturation transfer (paraCEST) is interference from endogenous tissue magnetization transfer contrast (MTC). The suitability of excitation-based frequency labeled exchange transfer (FLEX) to separate out such MTC effects in vivo was tested.

Methods

The FLEX sequence measures modulation of the water signal based on the chemical shift evolution of solute proton magnetization as a function of evolution time. Time-domain analysis of this water signal allows identification of different solute components and provides a mechanism to separate out the rapidly decaying MTC components with short effective transverse relaxation time ( math formula) values.

Results

FLEX imaging of paraCEST agents was possible in vitro in phantoms and in vivo in mouse kidneys and bladder. The results demonstrated that FLEX is capable of separating out the MTC signal from tissues in vivo while providing a quantitative exchange rate for the rapidly exchanging paraCEST water protons by fitting the FLEX time-domain signal to FLEX theory.

Conclusions

The first in vivo FLEX images of a paraCEST agent were acquired, which allowed separation of the tissue MTC components. These results show that FLEX imaging has potential for imaging the distribution of functional paraCEST agents in biological tissues. Magn Reson Med 71:286–293, 2014. © 2013 Wiley Periodicals, Inc.

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