Objective: In this study, we aimed to evaluate the diagnostic sensitivities of ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT in the primary tumor, and nodal, peritoneal and distant organ metastases of primary and recurrent gastric adenocarcinoma (GAc) with patient and lesion-based comparison. Materials and method: Twenty-one patients with histopathologically proven newly diagnosed or recurrent GAc who underwent ¹⁸F-FDG and ⁶⁸Ga-FAPI-04 imaging were included in the study. Both imaging techniques were evaluated visually according to the intensity of organ-based uptake. SUVmax and tumor-to-background ratio (TBR) values obtained from primary tumor/relapse and metastatic organs were compared statistically. Results: ⁶⁸Ga-FAPI-04 uptake was positive in all 15 newly diagnosed patients, while two patients among them who had mucinous and signet ring cell carcinoma did not exhibit ¹⁸F-FDG uptake. The sensitivity and specificity of ⁶⁸Ga-FAPI-04 PET/CT in detecting primary gastric were 100%, while the sensitivity and specificity of ¹⁸F-FDG were 86.6 and 100%, respectively. ⁶⁸Ga-FAPI-04 imaging revealed diffuse stomach uptake in seven patients, while ¹⁸F-FDG could only show two of them. The sensitivity and specificity of in-patient-based detection of lymph node metastases were 100 and 95.2%, respectively, while these values were 71.4 and 93.7%, respectively, for ¹⁸F-FDG. For peritoneal involvement ⁶⁸Ga-FAPI-04 had a sensitivity and specificity of 100%, whereas ¹⁸F-FDG had a sensitivity of 40% and a specificity of 100%. Conclusion: ⁶⁸Ga-FAPI-04 PET/CT is an imaging modality with the potential of yielding more sensitive and specific findings ¹⁸F-FDG PET/CT. This modality may help avoid invasive diagnostic procedures that may be frequently required in GAc.

Objective. The aim of this study is to investigate the uptake of ⁶⁸Ga-FAPI-04 in normal tissues and calculate standardized uptake values (SUVs) for various organs in the body. Methods. A total of 49 patients who underwent ⁶⁸Ga-FAPI-04 PET/CT were included in our study. The following organs were identified on CT images: brain, parotid, and submandibular glands, palatine tonsils, thyroid, lymph nodes (if present), breasts, lungs, thymus, left ventricle walls, mediastinal blood pool, vertebral bone marrow, liver, spleen, pancreas, stomach, small and large intestines, adrenal glands, kidneys, uterus, testes, and prostate. Median, minimum, and maximum values (max) and average (avg) values of standard uptake value (SUV) of tissues and organs were calculated. Results. The accumulation of ⁶⁸Ga-FAPI in normal organs showed variations. The cerebral/cerebellar cortex exhibited no ⁶⁸Ga-FAPI uptake, while the scalp showed low uptake. Low uptake was also observed in the lung parenchyma, esophagus, left ventricle walls, nipple, and glandular breast tissue. In the abdominopelvic area, the pancreas exhibited low uptake, which was higher in the tail region. Low uptake was observed in the renal cortex. Intense ⁶⁸Ga-FAPI uptake was observed throughout the uterus, which was higher in the corpus. There was no uptake of ⁶⁸Ga-FAPI in the bone cortex and medulla. Conclusion. We determined the physiological uptake and SUVmax of FAPI-04 in different tissues and organs and created a guide for researchers.

Aim: In this study, we aimed to compare the diagnostic accuracy of ¹⁸F−fluorodeoxyglucose (¹⁸F-FDG) and Gallium-68 labeled fibroblast activator protein inhibitor (⁶⁸Ga-FAPI)-04 PET/CT in the tumor–node–metastasis (TNM) staging of patients with nonsmall cell lung cancer (NSCLC) and investigate whether adenocarcinoma (ADC) and squamous cell cancer (SCC) exhibit different uptake patterns on ⁶⁸Ga-FAPI-04 PET/CT. Materials and method: Twenty-nine patients with a histopathologically-confirmed diagnosis of NSCLC, who had no history of previous radiation therapy or chemotherapy and underwent ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI-04 PET/CT imaging between January 2021 and December 2021 were included in this retrospective study. Staging was performed using the 8th edition of the TNM staging system on both ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI-04 PET/CT images. Standardized uptake value (SUV)_max and tumor-to-background ratios (TBR) were calculated on primary lesions and metastases. Results: There was no statistically significant difference in primary lesions in terms of SUV_max and TBR values. However, ⁶⁸Ga-FAPI-04 PET/CT was significantly superior to ¹⁸F-FDG PET/CT in terms of the number of lymph nodes and bone metastases revealed. The SUV_max and TBR values of lymph nodes, hepatic lesions and bone lesions were significantly higher on ⁶⁸Ga-FAPI-04 PET/CT than on ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI-04 PET/CT changed the disease stage of three patients (10.9%). The diagnostic accuracy of ⁶⁸Ga-FAPI-04 PET/CT was 100%, whereas the diagnostic accuracy of ¹⁸F-FDG PET/CT was 89.6% (P = 0.250). Conclusion: Although ⁶⁸Ga-FAPI-04 PET/CT detected more lesions and higher diagnostic accuracy than ¹⁸F-FDG PET/CT in NSCLC, neither method was statistically superior to each other in terms of diagnostic accuracy in TNM staging.