I am trying to perform some calibration experiment for AcidoCEST: a novel approach to measure in vivo pH. It uses Iodinated contrast agent that are also used in CT.
For my phantom experiment, I plan to bring T2 value ~100-200 ms range.
I have already tried MnCl2 and CuSO4; however, problem is that iodine interacts with Mn2+, Cu2+. So, R2 = 1/T2 decreases when the concentration of the Iodinated contrast agent increases. This is undesired and I believe that it would interfere with my experiment and make interpretation difficult.
Further, ideally the dopant molecule should not have any exchangeable protons.
Possibly, I can use Gd-based contrast agent. Dotarem (Gadoerate Meglumine) may not be suitable as meglumine has exchangeable protons. I think Gd-DTPA may be fine for my purpose. Though I am not a chemist; but, it seems that there are exchangeable protons on all Gd-contrast agent.
I would also appreciate if someone can suggest some other contrast agent.
I suspect the pKa of all the contrast agents are so low (less than 1) that exchange is not going to matter at biological pH. You need a reporting group that is titratable in the biological pH range (CEST uses the Amine exchange, while other MR methods have used Phosphorus or Fluorine chemical shift to report).
I am curious, what mechanism do you think is going to make T2 dependent on pH?
Regards,
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