Maybe he's confusing it with PET scans or perhaps gamma ray imaging with technetium (used for cancer imaging). Interestingly, the gadolinium in MRI contrast ag

Maybe he's confusing it with PET scans or perhaps gamma ray imaging with technetium (used for cancer imaging). Interestingly, the gadolinium in MRI contrast agents, while composed of stable isotopes, is a ferociously good thermal neutron absorber. The element is used in burnable absorbers in some reactors to keep reactivity level as the fuel is burned down.