Which of the following is used as a marker of cell proliferation in PET imaging?

18F-FLT is a radiotracer specifically designed to measure cell proliferation. It is a thymidine analog that is incorporated into DNA during the S-phase of the cell cycle. This property makes it particularly useful in PET imaging for assessing tumor growth and the effectiveness of cancer therapies, as actively proliferating cells will take up more of the tracer.

Unlike 18F-FDG, which primarily measures glucose metabolism and thus gives insights into metabolic activity rather than direct cell division, 18F-FLT provides a more specific indication of cellular proliferation. 11C-PK11195 is primarily used to evaluate inflammation and glial activation in the brain, while 11C-FMAU is another thymidine analog but is less commonly used than 18F-FLT for proliferation studies. Therefore, 18F-FLT is the preferred marker for assessing cell proliferation in PET imaging.