Value of Semi-Quantitative Parameters of 68 Ga-FAPI-04 PET/CT in Primary Malignant and Benign Diseases: A Comparison with 18 F-FDG.

Objectives: We aimed to compare the value of the semiquantitative parameters of 68 Ga-labeled FAP inhibitor ( 68 Ga-FAPI)-04 positron emission tomography/computed tomography (PET/CT) and 18 F-fluorodeoxyglucose ( 18 F-FDG) in diagnosing primary malignant and benign diseases. Materials and Methods: 18 F-FDG and 68 Ga-FAPI-04 PET/CT images of 80 patients were compared. Semiquantitative parameters, including maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), peak SUV by lean body mass (SULpeak), metabolic tumor volume (or tumor volume of FAPI; FAPI-TV), and TLG (or total lesion activity of FAPI; FAPI-TLA), were automatically obtained using the IntelliSpace Portal image processing workstation with a threshold of 40% SUVmax. The liver blood pool was measured as the background, and the tumor-to-background ratio (TBRliver) was calculated. Results: In all malignant lesions, FAPI-TV and FAPI-TLA were higher in 68 Ga-FAPI-04 PET/CT than in 18 F-FDG. In the subgroup analysis, 68 Ga-FAPI-04 had higher FAPI-TV and FAPI-TLA and lower SUVmax than 18 F-FDG had in group A, including gynecological tumor, esophageal, and colorectal cancers. However, six semiquantitative parameters were higher in group B (the other malignant tumors). For the benign diseases, SUVmax, SUVmean, SUVpeak, and SULpeak were lower in 68 Ga-FAPI-04 PET/CT than in 18 F-FDG. 68 Ga-FAPI-04 PET/CT showed a lower liver background and a higher TBRliver than 18 F-FDG did. 68 Ga-FAPI-04 PET/CT had higher accuracy, sensitivity, and specificity than 18 F-FDG had. Conclusion: More accurate semiquantitative parameters and lower abdominal background in 68 Ga-FAPI-04 PET/CT make it more competitive in the differential diagnosis of malignant and benign diseases than in 18 F-FDG.