Comparison of 18F-FDG and 67Ga-citrate in sarcoidosis imaging

Aim: 67Ga citrate has been used long and successfully to diagnose and stage sarcoidosis. 18F-fluorodeoxyglucose (18F-FDG) has been suggested as a positron emission tomography (PET) tracer for sarcoidosis imaging. This study aimed to analyze possible advantages of 18F-FDG-PET over 67Ga citrate scintigraphy during the primary assessment of patients with sarcoidosis. Patients and methods: twenty-four patients (11 men, 13 women, aged 52 years ± 12.4) with histologically proven sarcoidosis were investigated with 18F-FDG and 67Ga citrate. Equipment included a full-ring PET scanner (ECAT EXACT HR+, Siemens/CTI, Knoxville TN, USA) and a double-headed gamma camera (ECAM, Siemens, Illinois, USA) for scintigraphy. The mean time difference between the two studies was 6.5 days (range: 5-8 days). Results: there was a significant difference in the detection of pulmonary and nonpulmonary sarcoidosis lesions between planar 67Ga citrate scans and 18F-FDG-PET images (< 0.0021). A total of 64 lesions were detected with 67Ga citrate scans in the thorax and elsewhere with a mean of 2.6 lesions (4%) per patient, while 85 lesions were found with 18F-FDG-PET, with a mean of 3.5 lesions (4.1%) per patient. There was complete agreement between 18F-FDG and 67Ga citrate in thoracic manifestations in four (16.6%) patients, and in non-thoracic manifestations in five (20.8%) patients. The interobserver variability showed a kappa value of 0.79. Conclusion: 67Ga citrate and 18F-FDG are useful tracers for diagnostic evaluation of thoracic sarcoidosis. 18F-FDG seems to be more suitable for imaging the mediastinum, the bi-hilar lymph nodes, the posterior regions of the lungs and non-thoracic lesions. Further prospective studies are needed to clarify the role of both tracers in early diagnosis and staging of sarcoidosis, and to resolve questions concerning medical treatment and follow-up. (orig.)