⁶⁸Ga-FAPI (fibroblast activation protein-specific inhibitor) PET/CT was performed in a 56-year-old man with multiple liver masses, which were confirmed grade 2 well-differentiated neuroendocrine tumors with liver Tru-Cut biopsy. With ⁶⁸Ga-DOTATE PET/CT, primary tumor in the pancreas, multiple metastases in the liver and metastatic portocaval lymph node were detected. In ⁶⁸Ga-FAPI PET/CT imaging performed for comparison, it was seen that metastatic lesions in the liver were distinguished much better because of low background activity, and the primary tumor and metastatic lymph node were clearly selected. This case suggested that FAPI-bounded radionuclides may be useful in the evaluation and targeted therapy of neuroendocrine tumors.

⁶⁸Ga–fibroblast activation protein–specific inhibitor (FAPI)-04 PET/CT was performed in a 49-year-old woman diagnosed with breast cancer. In PET/CT imaging, intense ⁶⁸Ga-FAPI uptake was observed in the primary tumor, axillary lymph nodes, and also in the thyroid gland, whereas pathological ¹⁸F-FDG uptake was not observed in the thyroid gland. On thyroid ultrasonography, parenchyma was heterogeneous, and an area of focal thyroiditis was observed in the superior part of the right lobe. Biochemical parameters were found to be consistent with thyroiditis. This case shows that FAPI uptake in the thyroid gland may be associated with thyroiditis and should be evaluated clinically.

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.

This study aimed to compare the metabolic parameters obtained from 18fluorine-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) and gallium-68 (68Ga)-prostate-specific membrane antigen (PSMA) PET/CT and investigate the relationship between serum alpha-fetoprotein and PET scan parameters in patients with hepatocellular carcinoma. Fourteen patients were recruited after dynamic magnetic resonance imaging (MRI) of the upper abdomen, and 18F-FDG and 68Ga-PSMA PET/CT imaging studies were conducted. Regions of interest (ROIs) were drawn from lesion-free liver tissue, abdominal aorta (A), and right medial gluteal muscle (G) for the background activity. Maximum standard uptake value (SUVmax) of these regions were compared with the SUVmax of primary tumor (T). On visual assessment, five patients (36%) experienced low 18F-FDG uptake in the primary lesion, three patients (21%) experienced moderate uptake, and six patients (43%) experienced high uptake. However, only one patient (7%) showed low 68Ga-PSMA uptake, two patients (14%) showed moderate uptake, and 11 patients (79%) showed high uptake. Four patients with a low 18F-FDG uptake showed high 68Ga-PSMA uptake, while one patient exhibited low uptake with both 18F-FDG and 68Ga-PSMA. The number of lesions on 68Ga-PSMA PET/CT and MRI was significantly higher than 18F-FDG PET/CT (p=0.042 and 0.026, respectively). T/A and T/G values were significantly higher in 68Ga-PSMA than 18F-FDG (p=0.002 and 0.002, respectively). 68Ga-PSMA PET/CT is superior to 18F-FDG PET/CT in the staging of hepatocellular carcinoma. High 68Ga-PSMA uptake could be promising for PSMA-targeted radionuclide treatments.

⁶⁸Ga-fibroblast activation protein-specific inhibitor (FAPI)-04 PET/CT was performed in a patient with left lower outer quadrant breast cancer who had ¹⁸F-FDG PET/CT imaging. ⁶⁸Ga-FAPI-04 PET/CT showed higher accumulation of radiotracer in primary tumor and axillary lymph nodes than ¹⁸F-FDG PET/CT. In addition, focal increased FAPI uptake was observed in another nodular lesion in the lower inner quadrant in the same breast, which was considered malignant. However, Tru-Cut biopsy of this lesion was reported as benign lymphoid tissue. This case showed that all FAPI accumulation in breast tissue should not be interpreted in favor of malignancy; histopathological confirmation is required.

An 83-year-old man presented with abdominal pain, vomiting, and bloating. His abdominal CT revealed heterogeneous peritoneal thickening in the lower quadrants, which was more prominent in the pelvic region. ¹⁸F-FDG PET/CT performed to locate the primary tumor showed irregular peritoneal and omental thickening with low to moderate FDG uptake. ⁶⁸Ga–FAPI (fibroblast activation protein–specific inhibitor)–04 PET/CT of the patient, whose primary tumor could not be detected using FDG, showed high radiopharmaceutical uptake in the areas of heterogeneous thickening on peritoneal and serosal surfaces. Peritoneal Tru-Cut biopsy revealed malignant tumoral infiltration indicating mesothelioma. This case showed that ⁶⁸Ga-FAPI-04 PET/CT could be a promising radiopharmaceutical in the evaluation of peritoneal mesothelioma.