Used in positron emission tomography (PET) imaging as a radiolabeled tracer (typically [18F]-FLT) to monitor cellular proliferation, particularly in cancer research. It is taken up by nucleoside transporters, phosphorylated by thymidine kinase 1, and trapped in proliferating cells, reflecting DNA synthesis rates without significant incorporation into DNA. This makes it valuable for assessing tumor growth, treatment response, and prognosis in preclinical and clinical settings. It has also been studied for potential antiviral and anticancer therapeutic applications due to its interference with nucleotide metabolism.