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 pro-spective cohort study to explore the ability of Ga-68 fibroblast activation protein inhibitor (Ga-68-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, Ga-68-FAPI PET/CT and F-18-FDG PET/CT were conducted within 1 wk. The posi-tive rate and SUVmax of the lesions in the involved organs were com-pared 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 manifes-tations were intracranial infiltration (50%) and cutaneous infiltration (35.7%). Ga-68-FAPI PET/CT detected 64 of 67 lesions in 14 patients, whereas F-18-FDG PET/CT detected 51 of 67 lesions (P = 0.004). The SUVmax for Ga-68-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 Ga-68-FAPI PET/CT is superior to that of F-18-FDG PET/CT. Moreover, Ga-68-FAPI PET/CT has a better image contrast and higher SUVmax for lesions in multiple organs including the heart, lungs, peritoneum, and kidneys. Ga-68-FAPI PET/CT is a promising tool to assess pathologic features and disease extent in ECD patients.