Spin-lock imaging of exogenous exchange-based contrast agents to assess tissue pH.

Abstract

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 R1ρ , the spin lattice relaxation rate in the rotating frame, were derived from the behavior of R1ρ 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.

• Authors: Zhongliang Zu, Hua Li, Xiaoyu Jiang, John C Gore
• Journal: Magnetic resonance in medicine (Magn Reson Med) Vol. 79 Issue 1 Pg. 298-305 (Jan 2018) ISSN: 1522-2594 [Electronic] United States
• PMID: 28321903 (Publication Type: Journal Article)
• Copyright: © 2017 International Society for Magnetic Resonance in Medicine.

Chemical References

• Contrast Media
• Mannitol
• Iohexol

Topics

• Animals
• Brain (diagnostic imaging)
• Brain Neoplasms (diagnostic imaging)
• Contrast Media (chemistry)
• Glioblastoma (diagnostic imaging)
• Hydrogen-Ion Concentration
• Iohexol (chemistry)
• Magnetic Resonance Imaging (methods)
• Mannitol (chemistry)
• Models, Theoretical
• Phantoms, Imaging
• Rats