R1ρ sensitivity to pH and other compounds at clinically accessible spin-lock fields in the presence of proteins

Nana Owusu, Casey P. Johnson, William Kearney, Dan Thedens, John Wemmie, Vincent A. Magnotta

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Numerous human diseases involve abnormal metabolism, and proton exchange is an effective source of magnetic resonance imaging (MRI) contrast for assessing metabolism. One MRI technique that capitalizes on proton exchange is R1 relaxation in the rotating frame (R). Here, we investigated the sensitivity of R to various proton-exchange mechanisms at spin-lock pulses within Food and Drug Administration (FDA) safety guidelines for radiofrequency-induced heating. We systematically varied pH known to change the rate of proton exchange as well as the glucose and lysine concentrations, thus changing the number of amide, hydroxyl and amine exchangeable sites in a series of egg-white albumin phantoms. The resulting effects on quantitative relaxation time measurements of R, R1 and R2 were observed at 3 T. Using spin-lock amplitudes available for human imaging (less than 23.5 μT) at near physiologic temperatures, we found R was more sensitive to physiologic changes in pH than to changes in glucose and lysine concentrations. In addition, R was more sensitive to pH changes than R1 and R2. Models of proton exchange fitted to the relaxation measurements suggest that amide groups were the primary source of pH sensitivity. Together, these experiments suggest an optimal spin-lock amplitude for measuring pH changes while not exceeding FDA-subject heating limitations.

Original languageEnglish (US)
Article numbere4217
JournalNMR in biomedicine
Issue number2
StatePublished - Feb 1 2020

Bibliographical note

Publisher Copyright:
© 2019 John Wiley & Sons, Ltd.


  • R dispersion
  • glucose
  • lysine
  • multiparametric imaging
  • pH
  • physical phantom
  • temperature


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