PET stands for Positron Emission Tomography. The radioactive tracers emit positrons (antimatter), which then annihilate with electrons to produce the gamma rays that are detected. So it does use antimatter, just indirectly through the decay process.
I am familiar with PET. As we both agree, PET does not use antimatter directly, so this article is irrelevant to it (which is what the original comment was asking about).
Indeed, it would be quite difficult to smuggle some antimatter to a tumor. I'm saying that research in this particular area eventually led to practical application, PET scans.