Measuring in vivo tumor pHe with CEST-FISP MRI

Vipul R. Sheth, Yuguo Li, Liu Qi Chen, Christine M. Howison, Chris A. Flask, Mark D. Pagel

Research output: Contribution to journalArticlepeer-review


Paramagnetic chemical exchange saturation transfer (PARACEST) MRI contrast agents have been developed that can measure pH in solution studies, but these agents have not previously been detected in vivo. To use the PARACEST agent Yb-DO3A-oAA to measure the extracellular pH (pHe) in tumor tissue, a chemical exchange saturation transfer fast imaging with steady state precession MRI protocol was developed, the saturation period was optimized for sensitive chemical exchange saturation transfer (CEST) detection, and median filtering was used to remove artifacts in CEST spectra. These improvements were used to correlate pH with a ratio of two CEST effects of Yb-DO3A-oAA at a 7 T magnetic field strength (R2 = 0.99, standard deviation of precision = 0.011 pH units). The PARACEST agent could not be detected in tumor tissue following i.v. injection due to the low sensitivity of in vivo CEST MRI. Yb-DO3A-oAA was detected in tumor tissue and leg muscle after directly injecting the PARACEST agent into these tissues. The measured CEST effects were used to measure a tumor pH of 6.82 ± 0.21 and a leg muscle pH of 7.26 ± 0.14, and parametric pH maps were also generated from these tissue regions. These results demonstrated that tumor pHe can be measured with a PARACEST agent and a rapid CEST-MRI protocol.

Original languageEnglish (US)
Pages (from-to)760-768
Number of pages9
JournalMagnetic resonance in medicine
Issue number3
StatePublished - Mar 2012
Externally publishedYes


  • biophysics
  • contrast
  • contrast agents
  • molecular imaging
  • technical research
  • technique development

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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