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@ARTICLE{Stabinska:862748,
      author       = {Stabinska, Julia and Neudecker, Philipp and Ljimani,
                      Alexandra and Wittsack, Hans‐Jörg and Lanzman, Rotem
                      Shlomo and Müller‐Lutz, Anja},
      title        = {{P}roton exchange in aqueous urea solutions measured by
                      water‐exchange ({WEX}) {NMR} spectroscopy and chemical
                      exchange saturation transfer ({CEST}) imaging in vitro},
      journal      = {Magnetic resonance in medicine},
      volume       = {82},
      number       = {3},
      issn         = {1522-2594},
      address      = {New York, NY [u.a.]},
      publisher    = {Wiley-Liss},
      reportid     = {FZJ-2019-02990},
      pages        = {935-947},
      year         = {2019},
      abstract     = {PURPOSE:To characterize the proton exchange in aqueous urea
                      solutions using a modified version of the WEX II filter at
                      high magnetic field, and to assess the feasibility of
                      performing quantitative urea CEST MRI on a 3T clinical MR
                      system.METHODS:In order to study the dependence of the
                      exchange-rate constant ksw of urea as a function of pH and
                      T, the WEX-spectra were acquired at 600 MHz from urea
                      solutions in a pH range from 6.4 to 8.0 and a temperature
                      range from T=22∘C to 37∘C . The CEST experiments were
                      performed on a 3T MRI scanner by applying a train of 50
                      Gaussian-shaped pulses, each 100-millisecond long with a
                      spacing of 100 milliseconds, for saturation. Exchange rates
                      of urea were calculated using the (extended) AREX
                      metric.RESULTS:The results showed that proton exchange in
                      aqueous urea solutions is acid and base catalyzed with the
                      rate constants: ka=(9.95±1.1)×106 l/(mol·s) and
                      kb=(6.21±0.21)×106 l/(mol·s), respectively. Since the
                      urea protons undergo a slow exchange with water protons, the
                      CEST effect of urea can be observed efficiently at 3T.
                      However, in neutral solutions the exchange rate of urea is
                      minimal and cannot be estimated using the quantitative CEST
                      approach.CONCLUSIONS:By means of the WEX-spectroscopy, the
                      kinetic parameters of the proton exchange in urea solutions
                      have been determined. It was also possible to estimate the
                      exchange rates of urea in a broad range of pH values using
                      the CEST method at a clinical scanner.},
      cin          = {ICS-6},
      ddc          = {610},
      cid          = {I:(DE-Juel1)ICS-6-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551)},
      pid          = {G:(DE-HGF)POF3-551},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:31004385},
      UT           = {WOS:000485077600007},
      doi          = {10.1002/mrm.27778},
      url          = {https://juser.fz-juelich.de/record/862748},
}