One other "fun" use of perflurocarbons (like fluorinated crown ethers or cyclo-alkanes) is that, containing large amounts of 19F, they are MRI visible. So, you can directly image the compound in the lungs leading to some really striking images [1, 2] while they are in the gaseous phase, or indeed in the liquid phase
when one lung is partially inflated. I think that some compounds like these have been proposed for use in patients who have inhaled hot or burning gasses (viz: most likely blast/explosion/deflagration victims) and suffered an internal lung injury. Oedema can impair oxygen availability at the surface of the lung and it's my understanding that there is at least one or two research projects using PFCs as an intensive life-supporting measure as a consequence .
One can also do that with nuclear spin polarized 3He or xenon. The nuclei of these isotopes are sufficiently shielded from the environment that polarization (induced with circularly polarized light scattering off alkali vapor mixed with the inert gas) survives for quite a long time. The polarization is orders of magnitude stronger than that induced by magnetic fields in ordinary NMR.
And then you get the chemical shift differences of the dissolved phases when imaging with 129Xe as well – got to love SEOP and hyperpolarisation techniques in general! :-)
[1] https://onlinelibrary.wiley.com/doi/full/10.1002/jmri.26292?...
[2] https://onlinelibrary.wiley.com/doi/full/10.1002/mrm.28270?c...
[3] https://onlinelibrary.wiley.com/doi/full/10.1002/mrm.10008?c...