Early diagnosis and staging of paraquat-induced pulmonary fibrosis using [¹⁸F]F-FAPI-42 PET/CT imaging

Paraquat (PQ) -induced pulmonary fibrosis poses a significant medical challenge due to limited treatment options and high mortality rates. Consequently, there is an urgent need for early diagnosis and accurate staging to facilitate appropriate treatment strategies. In this study, we assessed the diagnostic potential of [¹⁸F]F-FAPI-42 PET/CT imaging for early detection and disease staging in a rat model of PQ-induced lung fibrosis.

After administering 80 mg/kg of PQ orally to Sprague-Dawley rats, we intravenously injected 3-3.5 MBq of [¹⁸F]F-FAPI-42 on day 7, 14, and 21 post-dosing. Dynamic PET/CT imaging was carried out for one hour immediately after the administration of [¹⁸F]F-FAPI-42. Subsequently, the lung tissues were collected for Hematoxylin and Eosin (HE) staining, Masson's trichrome staining, and NOTA-FAPI-04-MB fluorescent probe staining. Data analysis was performed using the Imalytics preclinical software, and the mean standardized uptake value (SUV_mean) was calculated.

PET signals revealed that in areas with evident lesions on CT, the SUV_mean on day 14 was significantly higher than on day 7 and 21, indicating that changes in fibrosis activity levels contribute to the staging of pulmonary fibrosis. Additionally, the NOTA-FAPI-04-MB fluorescent probe staining also demonstrated the most pronounced probe uptake on day 14. In regions without apparent lesions on CT, the SUV_mean gradually increased from day 7 to day 21, reflecting ongoing fibrotic activity. Moreover, HE staining and Masson's trichrome staining did not reveal pulmonary fibrosis, while PET imaging was able to detect it, serving the purpose of early diagnosis. At 30 min and 60 min, the target-to-background ratio (TBR) of the PQ groups on day 7, 14, and 21 was significantly higher than the control group, suggesting a high specificity of [¹⁸F]F-FAPI-42 binding to activated fibroblasts.

[¹⁸F]F-FAPI-42 PET/CT imaging enables early diagnosis and staging of PQ-induced pulmonary fibrosis, demonstrating its feasibility and potential for characterizing early disease stages.