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A Prospective Comparison of [18F]FAPI-42 and [68Ga]Ga-FAPI-04 PET/CT in Patients With Various Cancers


 Purpose: [18F]FAPI-42 is a new fibroblast activation protein (FAP) specific tracer used for cancer imaging. Here, we describe the in vivo evaluation of [18F]FAPI-42 and compared intra-individual biodistribution, tumor uptake, and detection ability to [68Ga]Ga-FAPI-04.Methods: A total of 22 patients with various types of cancer received [18F]FAPI-42 whole-body positron emission tomography/computed tomography (PET/CT). Among them, 4 patients underwent PET/CT scans, including an early dynamic 20-min, static 1-hour and static 2-hours. The in vivo biodistribution in normal organs and tumor uptake were semi-quantitatively evaluated using the standardized uptake value (SUV) and tumor-to-background ratio (TBR). Furthermore, both [18F]FAPI-42 and [68Ga]Ga-FAPI-04 PET/CT were performed in 12 patients to compare biodistribution, tumor uptake, and tumor detection ability.Results: [18F]FAPI-42 uptake in the tumors was rapid and reached a high level with an average SUVmax of 15.8 at 18 minutes, which stayed at a similarly high level to 2 hours. The optimal image acquisition time for [18F]FAPI-42 was determined to be 1 hour post injection. Compared to [68Ga]Ga-FAPI-04, [18F]FAPI-42 had a higher uptake in the parotid, salivary gland, thyroid, and pancreas (P < 0.05). For tumor detection, [18F]FAPI-42 had a high uptake and could be clearly visualized in the lesions. [18F]FAPI-42 and [68Ga]Ga-FAPI-04 showed the same detectability for 144 positive lesions. In addition, [18F]FAPI-42 had a higher SUVmax in liver and bone lesions (P < 0.05) and higher TBRs in liver, bone, lymph node, pleura and peritonea lesions (all P < 0.05).Conclusion: The present study demonstrates that [18F]FAPI-42 is a good tracer for imaging malignant tumors and exhibited comparable lesion detectability to [68Ga]Ga-FAPI-04. The 1-hour scan is an appropriate time for tumor detection and is superior to the early 10-min scan for the detection of small lesions.Trial registration Chinese Clinical Trial Registry (ChiCTR2100045757)