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 SUVmax 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 SUVmax for 68Ga-FAPI PET/CT was significantly higher than the SUVmax 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 SUVmax 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.