The group Allison is referring to (Hyare et al., 2008) found that storing tissue in Fomblin for 2 days prior to MRI had no effect on scan or histology results when compared to matched samples stored in 10% formol-saline.

Synopsis: Formalin-fixed mouse brain tissue placed in Fomblin for 2 days prior to T1, T2, DWI, and MTR scans @ 9.4T produced the same results as formalin-fixed controls placed in 10% formol-saline solution 2 days prior to scanning. Both were scanned in Fomblin. They compared ROI-based quantitative MR measures, anatomical & cellular histology, and immunohistochemical staining.

Fluorinert has been used in a number of studies. A quick search came back with +5 exvivo studies since 2004 using Fluorinert as an in-scan solution - typically Flourinert FC-77, not FC-3283.

3M Fluorinert Electronic Liquids for Electronics:

Studies using Flourinert: Noristani et al., 2015, Colon-Perez et al., 2015, Kovačević et al., 2004, etc. (,22&q=ex+vivo+mri+fluorinert)