title: MRI CEST at 1T with large µeff Ln(3+) complexes T m(3+)-HPDO3A: An efficient MRI pH reporter.
abstract: OBJECTIVE
  Chemical exchange saturation transfer (CEST) sensitivity relies on the prototropic exchange rate kex between the agent and the "bulk" water protons. To exploit large kex, a large frequency separation (Δω) between the pools of exchanging protons is necessary. For this reason, high magnetic fields are preferred. Herein it is shown that the use of paramagnetic CEST agents based on lanthanide (III) ions with large effective magnetic moments allows the carrying out of CEST experiments at the relatively low field strength of 1 tesla (T).
  
  
  METHODS
  Measurements were performed on a 1T MR-scanner using continuous wave (cw)-presaturation with a spin echo sequence. ParaCEST complexes have been synthetized by mixing the ligand and Ln(III)Cl3 in a stoichiometric ratio at room temperature and pH 7.
  
  
  RESULTS
  Different lanthanide chelates were investigated (Tm-, Dy-, Yb-, Eu-HPDO3A, and Eu-DOTAMGly). Ratiometric (Tm-HPDO3A) and selective detection (Eu-DOTAMGly and Tm-HPDO3A) experiments have been proven feasible in vivo.
  
  
  CONCLUSIONS
  In vitro experiments demonstrated the feasibility of the CEST methodology at 1T for nearly every paraCEST candidate under investigation, except for Eu-HPDO3A. Among the studied compounds, Tm-HPDO3A proved suitable for the application of a ratiometric method for assessing pH both in vitro and in vivo.
authors: Technical University Munich, Klinikum rechts der Isar, München, Germany.
authors: Giaime
authors: G
authors: Rancan
authors: University of Turin, Molecular Imaging Center, Torino, Italy.
authors: Daniela
authors: D
authors: Delli Castelli
authors: University of Turin, Molecular Imaging Center, Torino, Italy.
authors: Silvio
authors: S
authors: Aime
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000138:chemical synthesis; D005240:Feasibility Studies; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D051381:Rats; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D001743:Urinary Bladder / Q000033:anatomy & histology* / Q000737:chemistry*
chemical_list: C544520:10-(2-hydroxypropyl)-1,4,7-tetraazacyclododecane-1,4,7-triacetic acid; D003287:Contrast Media; D006573:Heterocyclic Compounds, 1-Ring; D028581:Lanthanoid Series Elements
keywords: CEST; HPDO3A; low-field CEST; pH mapping; paraCEST