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

Objectives: We compared the value of the semiquantitative parameters of ⁶⁸Ga-labeled FAP inhibitor (⁶⁸Ga-FAPI)-04 positron emission tomography/computed tomography (PET/CT) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) in diagnosing primary malignant and benign diseases. Materials and Methods: ¹⁸F-FDG and ⁶⁸Ga-FAPI-04 PET/CT images of 80 patients were compared. Semiquantitative parameters, including maximum standardized uptake value (SUV_max), mean SUV (SUV_mean), peak SUV (SUV_peak), peak SUV by lean body mass (SUL_peak), 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% SUV_max. 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 ⁶⁸Ga-FAPI-04 PET/CT than in ¹⁸F-FDG. In the subgroup analysis, ⁶⁸Ga-FAPI-04 had higher FAPI-TV and FAPI-TLA and lower SUV_max than ¹⁸F-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, SUV_max, SUV_mean, SUV_peak, and SUL_peak were lower in ⁶⁸Ga-FAPI-04 PET/CT than in ¹⁸F-FDG. ⁶⁸Ga-FAPI-04 PET/CT showed a lower liver background and a higher TBRliver than ¹⁸F-FDG did. ⁶⁸Ga-FAPI-04 PET/CT had higher accuracy, sensitivity, and specificity than ¹⁸F-FDG had. Conclusion: More accurate semiquantitative parameters and lower abdominal background in ⁶⁸Ga-FAPI-04 PET/CT make it more competitive in the differential diagnosis of malignant and benign diseases than in ¹⁸F-FDG.