Good day. My data are MRI scans of mice with heterotopic tumors before and after magnetite nanoparticles intravenous injections. I'd like to calculate - how much darker a tumor does appear 6h and 24h post injection than before.

I'm trying to calculate CNR but have no clear idea how to do it.

I would greatly appreciate for any help (relevant references and so on).

I guess my main problem is to find proper reference for comparison. I had no water in eppendorf sample (for instance) near each mouse during each scan, I'm trying to use muscles as a reference, but their signal (and SNR) also changes from scan to scan.

Thank you in advance.