Evaluation of DNA synthesis with carbon-11-labeled 4′-thiothymidine

Figure 1 Rationale for designing an ideal DNA synthesis tracer for cell proliferation imaging. The ideal tracer must block catabolism by thymidine phosphorylase, while retaining anabolism by the salvage pathway. ENT1: Equilibrative nucleoside transporter 1; TDP: Thymidine di-phosphate; TMP: Thymidine monophosphate; TTP: Thymidine tri-phosphate; TK1: Thymidine kinase 1; TK2: Thymidine kinase 2; TP: Thymidine phosphorylase.