Full Paper

Optimized MRI contrast for on-resonance proton exchange processes of PARACEST agents in biological systems

  1. Alex X. Li1,2,
  2. Mojmir Suchy1,3,
  3. Craig K. Jones1,
  4. Robert H. E. Hudson3,
  5. Ravi S. Menon1,2,
  6. Robert Bartha1,2,*

Article first published online: 24 SEP 2009

DOI: 10.1002/mrm.22134

Issue

Magnetic Resonance in Medicine

Magnetic Resonance in Medicine

Volume 62, Issue 5, pages 1282–1291, November 2009

Additional Information

How to Cite

Li, A. X., Suchy, M., Jones, C. K., Hudson, R. H. E., Menon, R. S. and Bartha, R. (2009), Optimized MRI contrast for on-resonance proton exchange processes of PARACEST agents in biological systems. Magn Reson Med, 62: 1282–1291. doi: 10.1002/mrm.22134

Author Information

  1. 1

    Center for Functional and Metabolic Mapping, Robarts Research Institute, London, Ontario, Canada

  2. 2

    Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada

  3. 3

    Department of Chemistry, University of Western Ontario, London, Ontario, Canada

*Center for Functional and Metabolic Mapping, Robarts Research Institute, 100 Perth Drive, P.O. Box 5015, London, Ontario, N6A 5K8 Canada

Publication History

  1. Issue published online: 28 OCT 2009
  2. Article first published online: 24 SEP 2009
  3. Manuscript Accepted: 16 JUN 2009
  4. Manuscript Revised: 13 MAY 2009
  5. Manuscript Received: 27 JAN 2009

Funded by

  • National Science and Engineering Research Council of Canada (NSERC)
  • Ontario Institute for Cancer Research
  • Canadian Institutes of Health Research (the University of Western Ontario Strategic Training Program in Cancer Research and Technology Transfer, and a Research Resource Grant)
  • Ivey-BMO Financial Group Scientist in Brain Disorders Imaging Award

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Keywords:

  • PARACEST contrast agent;
  • chemical exchange;
  • CEST;
  • magnetization transfer;
  • OPARACHEE;
  • macromolecules

Abstract

Image contrast associated with paramagnetic chemical exchange saturation transfer agents can be generated by off-resonance irradiation of agent-bound water or amide protons or on-resonance irradiation of bulk water. Previously, a four-pool model was developed to describe an in vivo system. The model incorporated the magnetization transfer effect from macromolecules when using off-resonance irradiation. In the current study, this four-pool model is modified to describe the in vivo system when using on-resonance irradiation. The influences of pulse power, pulse duration, the chemical shift of bound water, the proton exchange rate between bulk water and bound water, and agent concentration on the on-resonance paramagnetic agent chemical exchange effects were simulated using a WALTZ-16 pulse train in the absence and presence of the macromolecule pool. The results demonstrated that while contrast increases with pulse duration in aqueous solution, there is an optimal pulse duration that maximizes on-resonance paramagnetic agent chemical exchange effects contrast in vivo. This predication was verified by experimental spectroscopic and imaging results from aqueous solution, bovine serum albumin phantoms, and a tissue phantom containing thulium-DOTAM (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide)-glycine-lysine. This model can be used to optimize sequence parameters to maximize in vivo on-resonance paramagnetic agent chemical exchange effects contrast. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

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