⁶⁸Ga-DOTA-FAPI-04 PET/MR in the Evaluation of Gastric Carcinomas: Comparison with ¹⁸F-FDG PET/CT

We sought to evaluate the performance of ⁶⁸Ga-DOTA-FAPI-04 (⁶⁸Ga-FAPI) PET/MR for the diagnosis of primary tumor and metastatic lesions in patients with gastric carcinomas and to compare the results with those of ¹⁸F-FDG PET/CT. Methods: Twenty patients with histologically proven gastric carcinomas were recruited, and each patient underwent both ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI PET/MR. A visual scoring system was established to compare the detectability of primary tumors and metastases in different organs or regions (the peritoneum, abdominal lymph nodes, supradiaphragmatic lymph nodes, liver, ovary, bone, and other tissues). The original SUVmax and normalized SUVmax (calculated by dividing a lesion’s original SUVmax with the SUVmean of the descending aorta) of selected lesions on both ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI PET/MR were measured. Original/normalized SUVmax-FAPI and SUVmax-FDG were compared for patient-based (including a single lesion with the highest activity uptake in each organ/region) and lesion-based (including all lesions [≤5] or the 5 lesions with highest activity [>5]) analyses, respectively. Results: The 20 recruited patients (median age: 56.0 y; range: 29–70 y) included 9 men and 11 women, 14 patients for initial staging and 6 for recurrence detection. ⁶⁸Ga-FAPI PET was superior to ¹⁸F-FDG PET for primary tumor detection (100.00% [14/14] vs. 71.43% [10/14]; P = 0.034), and the former had higher tracer uptake levels (P < 0.05). ⁶⁸Ga-FAPI PET was superior to ¹⁸F-FDG PET in both patient-based and lesion-based evaluation except for the metastatic lesions in supradiaphragmatic lymph nodes and ovaries. Additionally, multiple sequences of MR images were beneficial for the interpretation of hepatic metastases in 3 patients, uterine and rectal metastases in 1 patient, ovarian lesions in 7 patients, and osseous metastases in 2 patients. Conclusion:⁶⁸Ga-FAPI PET/MR outperformed ¹⁸F-FDG PET/CT in visualizing the primary and most metastatic lesions of gastric cancer and might be a promising method, with the potential of replacing ¹⁸F-FDG PET/CT.