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Spin‐lock imaging of exogenous exchange‐based contrast agents to assess tissue pH
Author(s) -
Zu Zhongliang,
Li Hua,
Jiang Xiaoyu,
Gore John C.
Publication year - 2018
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26681
Subject(s) - iohexol , chemistry , contrast (vision) , magnetic resonance imaging , nuclear magnetic resonance , computer science , radiology , medicine , physics , artificial intelligence , biochemistry , renal function
Purpose Some X‐ray contrast agents contain exchangeable protons that give rise to exchange‐based effects on MRI, including chemical exchange saturation transfer (CEST). However, CEST has poor specificity to explicit exchange parameters. Spin‐lock sequences at high field are also sensitive to chemical exchange. Here, we evaluate whether spin‐locking techniques can detect the contrast agent iohexol in vivo after intravenous administration, and their potential for measuring changes in tissue pH. Methods Two metrics of contrast based on R 1ρ , the spin lattice relaxation rate in the rotating frame, were derived from the behavior of R 1ρ at different locking fields. Solutions containing iohexol at different concentrations and pH were used to evaluate the ability of the two metrics to quantify exchange effects. Images were also acquired from rat brains bearing tumors before and after intravenous injections of iohexol to evaluate the potential of spin‐lock techniques for detecting the agent and pH variations. Results The two metrics were found to depend separately on either agent concentration or pH. Spin‐lock imaging may therefore provide specific quantification of iohexol concentration and the iohexol‐water exchange rate, which reports on pH. Conclusions Spin‐lock techniques may be used to assess the dynamics of intravenous contrast agents and detect extracellular acidification. Magn Reson Med 79:298–305, 2018. © 2017 International Society for Magnetic Resonance in Medicine.