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

Chien Yuan Lin, Nirbhay N. Yadav, James Ratnakar, A. Dean Sherry, Peter C.M. Van Zijl

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


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 (T2*) 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.

Original languageEnglish (US)
Pages (from-to)286-293
Number of pages8
JournalMagnetic resonance in medicine
Issue number1
StatePublished - Jan 2014


  • chemical exchange saturation transfer
  • exchange rate
  • magnetization transfer
  • paramagnetic contrast agent

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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