Performance of 68Ga-Labeled Fibroblast Activation Protein Inhibitor PET/CT in Evaluation of Erdheim-Chester Disease: A Comparison with 18F-FDG PET/CT.

Erdheim-Chester disease (ECD) involves multiple organs and tissues and has diverse manifestations, which makes it difficult to distinguish lesions caused by ECD from those caused by other diseases. Variable degrees of fibrosis are present in ECD. Therefore, we conducted a prospective cohort study to explore the ability of ⁶⁸Ga fibroblast activation protein inhibitor (⁶⁸Ga-FAPI) PET/CT to detect lesions in ECD patients. Methods: Fourteen patients diagnosed with ECD, as confirmed by histology, were included in this study. For every patient, ⁶⁸Ga-FAPI PET/CT and ¹⁸F-FDG PET/CT were conducted within 1 wk. The positive rate and SUV_max of the lesions in the involved organs were compared between the examinations. Results: The most commonly involved organs were bone (100%), heart (57.1%), lung (57.1%), kidney (42.9%), and peritoneum or omentum (35.7%); other common manifestations were intracranial infiltration (50%) and cutaneous infiltration (35.7%). ⁶⁸Ga-FAPI PET/CT detected 64 of 67 lesions in 14 patients, whereas ¹⁸F-FDG PET/CT detected 51 of 67 lesions (P = 0.004). The SUV_max for ⁶⁸Ga-FAPI PET/CT was significantly higher than the SUV_max for ¹⁸F-FDG PET/CT of the heart (4.9 ± 2.4 vs. 2.8 ± 1.2, respectively; P = 0.050), lung or pleura (6.8 ± 4.9 vs. 3.1 ± 1.3, respectively; P = 0.025), peritoneum or omentum (5.7 ± 3.6 vs. 2.8 ± 1.7, respectively; P = 0.032), and kidney or perinephric infiltration (4.9 ± 1.2 vs. 2.9 ± 1.1, respectively; P = 0.009). Conclusion: The detectivity of ⁶⁸Ga-FAPI PET/CT is superior to that of ¹⁸F-FDG PET/CT. Moreover, ⁶⁸Ga-FAPI PET/CT has a better image contrast and higher SUV_max for lesions in multiple organs including the heart, lungs, peritoneum, and kidneys. ⁶⁸Ga-FAPI PET/CT is a promising tool to assess pathologic features and disease extent in ECD patients.