PMC

Dynamic changes in probe uptake; average of three volunteers per probe. Uptake is expressed as standardized uptake value (SUV_mean). ¹⁸F-FAC activity in liver and spleen decreased over time while liver uptake of L-¹⁸F-FAC and L-¹⁸F-FMAC increased slightly. Bone marrow uptake was lowest for ¹⁸F-FAC. Uptake is also noted in salivary glands and muscles (most prominently for ¹⁸F-FAC)

a The dCK-dependent nucleoside analog prodrug gemcitabine (dFdC) and ¹⁸F-FAC analogs share a common transport (ENT1) and phosphorylation (dCK) mechanism. Both gemcitabine and ¹⁸F-FAC are subject to deamination by cytidine deaminase (CDA). 5′-NT 5′-nucleotidase, MP monophosphate, TP triphosphate. b FDA-approved drugs that require dCK for their pharmacodynamic effects and the time line of their approval. Note the diversity of the chemical structures of these drugs, indicating the ability of dCK to phosphorylate both pyrimidine and purine analogs

¹⁸F-FAC images obtained in a patient with diffuse large B-cell lymphoma. The CT scan (left panel) shows extensive left axillary lymphadenopathy (arrow). This corresponds to a region of increased tracer uptake on the PET images suggesting that dCK expression of this lesion is high. B bone marrow, Bl bladder, K kidney, L liver, LA lymphadenopathy, M myocardium, S spleen. The scan was started 30 min after administration of 300 MBq of ¹⁸F-FAC. See Table  for effective dose estimates

Projection images obtained in three healthy volunteers using different FAC analogs. Organs are indicated by arrows (B bone marrow, Bl bladder, K kidney, L liver, M myocardium, S spleen, SG salivary gland). Note the high splenic uptake for ¹⁸F-FAC while hepatic uptake was highest for L-¹⁸F-FAC and L-¹⁸F-FMAC. Bone marrow was visualized with all three tracers; marked tracer clearance is seen from kidneys into the bladder. The images are scaled to the maximum liver uptake, i.e., SUV 1.7 for the left panel, SUV 6.8 for the middle panel, and SUV 4.9 for the right panel; this permits direct comparison

Selected axial slices of PET/CT fusion (a), CT (b), and PET (c) obtained in a patient with metastatic ovarian cancer, demonstrating L-¹⁸F-FMAC uptake in a metastatic lesion located in the gastric antrum. On PET/CT fusion images (a) physiologic uptake of L-¹⁸F-FMAC is seen in the liver (yellow arrow) and pancreas (blue arrow); excreted L-¹⁸F-FMAC is seen in both kidneys (white arrows). Incidental note is made of a large right renal cyst (white arrowhead). The scan was started 26 min after administration of 344 MBq of the radiopharmaceutical. Table  provides absorbed dose estimates