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Increased CEST specificity for amide and fast-exchanging amine protons using exchange-dependent relaxation rate.

Xiao-Yong Zhang1,2, Feng Wang1,2, Junzhong Xu1,2,3,4

  • 1Vanderbilt University Institute of Imaging Science, Nashville, TN, USA.

NMR in Biomedicine
|December 2, 2017
PubMed
Summary

This study introduces an exchange-dependent relaxation rate (Rex) to improve the specificity of chemical exchange saturation transfer (CEST) imaging. Rex effectively filters overlapping signals, enhancing the detection of amides and amines for better molecular imaging.

Keywords:
APTCESTMRIfast-exchanging aminespecificity

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Area of Science:

  • Magnetic Resonance Imaging
  • Biophysical Chemistry
  • Molecular Imaging

Background:

  • Chemical exchange saturation transfer (CEST) imaging enhances detection sensitivity for molecules like proteins and neurotransmitters.
  • CEST imaging faces specificity challenges due to confounding factors like direct water saturation, semi-solid magnetization transfer, and overlapping signals.
  • Existing methods struggle to fully resolve overlapping CEST signals, particularly from different amine and amide proton pools.

Purpose of the Study:

  • To develop a novel method using exchange-dependent relaxation rate (Rex) to improve the specificity of CEST imaging.
  • To differentiate and isolate amide proton transfer (APT) signals from interfering fast-exchanging amine signals.
  • To enhance the specificity of CEST imaging for both amides and fast-exchanging amines.

Main Methods:

  • Application of an exchange-dependent relaxation rate (Rex) model.
  • Simulations to analyze the distinct power dependencies of amides and amines.
  • Utilizing Rex as a frequency filter to reduce signals near the water resonance.

Main Results:

  • Simulations showed distinct irradiation power dependencies for slowly exchanging amides and fast-exchanging amines.
  • Rex acts as a high-pass filter, selectively reducing CEST signals closer to the water frequency.
  • Rex introduces Lorentzian lineshapes for fast-exchanging amines, distinguishing them from other signals.

Conclusions:

  • The Rex method effectively isolates APT signals from amine signals by exploiting differences in exchange rates and power dependencies.
  • Rex significantly enhances the specificity of CEST imaging for amides and fast-exchanging amines.
  • This approach offers improved molecular composition information by overcoming CEST specificity limitations.