title: A method for accurate pH mapping with chemical exchange saturation transfer (CEST) MRI.
abstract: Chemical exchange saturation transfer (CEST) MRI holds enormous promise for imaging pH. Whereas the routine CEST-weighted MRI contrast is complex and susceptible to confounding factors such as labile proton ratio, chemical shift, bulk water relaxation and RF saturation, ratiometric CEST imaging simplifies pH determination. However, the conventional ratiometric CEST (RCEST) MRI approach is limited to CEST agents with multiple exchangeable groups. To address this limitation, RF power-based ratiometric CEST (PRCEST) imaging has been proposed that ratios CEST effects obtained under different RF power levels. Nevertheless, due to concomitant RF saturation (spillover) effect, the recently proposed PRCEST imaging is somewhat dependent on parameters including bulk water relaxation time and chemical shift. Herein we hypothesized that RF power-based ratiometric analysis of RF spillover effect-corrected inverse CEST asymmetry (PRICEST) provides enhanced pH measurement. The postulation was verified numerically, and validated experimentally using an in vitro phantom. Briefly, our study showed that the difference between MRI-determined pH (pHMRI ) and electrode-measured pH being 0.12 ± 0.13 and 0.04 ± 0.03 for PRCEST and PRICEST imaging, respectively, and the newly proposed PRICEST imaging provides significantly more accurate pH determination than PRCEST imaging (P < 0.01, Wilcoxon signed-rank test). Notably, the exchange rate shows dominantly base-catalysed relationship with pH, independent of creatine concentration (P > 0.10, Analysis of Covariance). In addition, the derived labile proton ratio linearly scales with creatine concentration (P < 0.01, Pearson Regression). To summarize, PRICEST MRI provides concentration-independent pH imaging, augmenting prior quantitative CEST methods for accurate pH mapping. Copyright © 2015 John Wiley & Sons, Ltd.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Phillip Zhe
authors.identifier: 0000-0003-4872-1192
authors.initials: PZ
authors.lastname: Sun
authors.affiliation: Department of Math and Applied Mathematics, Hanshan Normal University, Chaozhou, China.|Department of Radiology, 2nd Affiliated Hospital of Shantou University Medical College, Shantou, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Xiao
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Iris Yuwen
authors.initials: IY
authors.lastname: Zhou
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Yingkun
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Department of Radiology, 2nd Affiliated Hospital of Shantou University Medical College, Shantou, China.
authors.forename: Renhua
authors.initials: R
authors.lastname: Wu
mesh_terms: D006863:Hydrogen-Ion Concentration; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008722:Methods; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D014867:Water
chemical_list: D014867:Water
keywords: MRI; chemical exchange saturation transfer (CEST); pH; quantitative CEST (qCEST); ratiometric CEST MRI