title: Quantified pH imaging with hyperpolarized (13) C-bicarbonate.
abstract: OBJECTIVE
  Because pH plays a crucial role in several diseases, it is desirable to measure pH in vivo noninvasively and in a spatially localized manner. Spatial maps of pH were quantified in vitro, with a focus on method-based errors, and applied in vivo.
  
  
  METHODS
  In vitro and in vivo (13) C mapping were performed for various flip angles for bicarbonate (BiC) and CO2 with spectral-spatial excitation and spiral readout in healthy Lewis rats in five slices. Acute subcutaneous sterile inflammation was induced with Concanavalin A in the right leg of Buffalo rats. pH and proton images were measured 2 h after induction.
  
  
  RESULTS
  After optimizing the signal to noise ratio of the hyperpolarized (13) C-bicarbonate, error estimation of the spectral-spatial excited spectrum reveals that the method covers the biologically relevant pH range of 6 to 8 with low pH error (< 0.2). Quantification of pH maps shows negligible impact of the residual bicarbonate signal. pH maps reflect the induction of acute metabolic alkalosis. Inflamed, infected regions exhibit lower pH.
  
  
  CONCLUSIONS
  Hyperpolarized (13) C-bicarbonate pH mapping was shown to be sensitive in the biologically relevant pH range. The mapping of pH was applied to healthy in vivo organs and interpreted within inflammation and acute metabolic alkalosis models.
authors.affiliation: Technische Universität München, Institute of Medical Engineering, Munich, Germany.
authors.forename: David Johannes
authors.initials: DJ
authors.lastname: Scholz
authors.affiliation: GE Global Research, Munich, Germany.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Janich
authors.affiliation: Technische Universität München, Institute of Medical Engineering, Munich, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Köllisch
authors.affiliation: GE Global Research, Munich, Germany.
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Schulte
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark.|Department of Electrical Engineering, Technical University of Denmark, Kgs Lyngby, Denmark.|GE Healthcare, Broendby, Denmark.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Ardenkjaer-Larsen
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Frank
authors.affiliation: Technische Universität München, Institute of Medical Engineering, Munich, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Haase
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.affiliation: GE Global Research, Munich, Germany.
authors.forename: Marion I
authors.initials: MI
authors.lastname: Menzel
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002247:Carbon Isotopes; D005552:Forelimb; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000378:metabolism*; D019047:Phantoms, Imaging; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D051381:Rats; D011915:Rats, Inbred BUF; D011917:Rats, Inbred Lew; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio
chemical_list: D001639:Bicarbonates; D002247:Carbon Isotopes
keywords: MRI; NMR spectroscopy; bicarbonate; hyperpolarized 13C; in vivo; pH