Imaging the inflammatory activity of sarcoidosis: Sensitivity and inter observer agreement of ⁶⁷Ga imaging and ¹⁸F-FDG PET

Aim. The aim of this study was to investigate sensitivity of ⁶⁷Ga imaging and ¹⁸F-FDG PET for sarcoidosis activity and their inter observer variability. Methods. Thirty-four newly diagnosed, histologically proven sarcoidosis patients were analyzed prospectively. ⁶⁷Ga imaging and ¹⁸F-FDG PET were performed, the presence of pulmonary and extra pulmonary lesions was evaluated and inter observer variability of both techniques was assessed. Results. Overall sensitivity to detect active sarcoidosis was 88% for ⁶⁷Ga imaging and 97% for ¹⁸F-FDG PET. Although these results were not significantly different, ¹⁸F-FDG PET detected more lesions in the mediastinum (P<0.05), hila (P<0.05), lymph nodes (P<0.001) and extra pulmonary regions in general (P<0.001). Inter observer agreement was poor to moderate for ⁶⁷Ga imaging (kappa 0.19-0.59) and good to very good for ¹⁸F-FDG PET (kappa 0.65-1.00). Conclusion. ¹⁸F-FDG PET is more sensitive than ⁶⁷Ga imaging in the assessment of sarcoidosis activity with regard to the mediastinum, hila, lymph nodes and extra pulmonary lesions in general. Furthermore, ¹⁸F-FDG PET demonstrates a very good inter observer agreement in contrast with ⁶⁷Ga imaging and ¹⁸F-FDG PET is therefore the nuclear imaging technique of choice in sarcoidosis assessment.