First total-body kinetic modeling and parametric imaging of dynamic ⁶⁸Ga-FAPI-04 PET in pancreatic and gastric cancer

Abstract

Background: Fibroblast activation protein inhibitor (FAPI) is an ideal diagnostic and therapeutic target in malignant tumors. However, the knowledge of kinetic modelling and parametric imaging of ⁶⁸Ga-FAPI is limited. Purpose: To explore the pharmacokinetics of ⁶⁸Ga-FAPI-04 PET/CT in pancreatic cancer and gastric cancer and to conduct parametric imaging of dynamic total-body data compared to standardized uptake value (SUV) imaging. Methods: Dynamic total-body ⁶⁸Ga-FAPI-04 PET/CT (with an AFOV of 194 cm) was performed on thirteen patients. The lesion time activity curves (TACs) were fitted by three-compartment models and multigraphical models. The kinetics parameters derived from the two-tissue reversible compartment model (2T4K) and multigraphical models were analyzed. Parametric 𝑉𝑡 imaging was generated using the 2T4K and Logan model, and their performances were evaluated compared to SUV images. Results: 2T4K had the lowest Akaike Information Criterion (AIC) value and its fitting curves matched excellently with the origin TACs. Visual assessment revealed that the 𝑉𝑡 (2T4K) images and 𝑉𝑡 (Logan with SC) images both showed less image noise and higher lesions conspicuity compared to SUV images. Objective image quality assessment demonstrated that parametric 𝑉𝑡 (2T4K) images and parametric 𝑉𝑡 (Logan with SC) images had a 5.0-fold and 5.0-fold higher average signal-to-noise ratio (SNR), and 3.6-fold and 4.1-fold higher average contrast-to-noise ratio (CNR) compared to conventional SUV images, respectively. In addition, no significant differences in SNR and CNR of pathological lesions were observed between parametric 𝑉𝑡 (2T4K) images and Parametric 𝑉𝑡 (Logan with SC) images (p all ＞0.05). Conclusion: The 2T4K model was the preferred compartment model. Total-body parametric imaging of ⁶⁸Ga-FAPI-04 PET yielded superior quantification beyond SUV with enhanced lesion contrast, which may serve as a promising imaging method for early diagnosis, to better reflect tumor characterization, or to allow evaluation of treatment response. 𝑉𝑡 (2T4K) images are comparable in image quality and superior to 𝑉𝑡 (Logan with SC) images in lesions conspicuity, however 𝑉𝑡 (Logan with SC) images presented an appealing alternative to 𝑉𝑡 (2T4K) images due to their simplicity.