Comparative Evaluation of ¹⁸F-FDG PET and ⁶⁷Ga Scintigraphy in Patients with Sarcoidosis

Abstract

⁶⁷Ga scintigraphy has been used for years in sarcoidosis for diagnosis and the extent of the disease. However, little information is available on the comparison of ¹⁸F-FDG PET and ⁶⁷Ga scintigraphy in the assessment of sarcoidosis. The purpose of this study was to compare the uptake of ¹⁸F-FDG and ⁶⁷Ga in the evaluation of pulmonary and extrapulmonary involvement in patients with sarcoidosis. Methods: Eighteen patients with sarcoidosis were examined. ¹⁸F-FDG PET was performed at 1 h after injection of 185−200 MBq ¹⁸F-FDG. ⁶⁷Ga whole-body planar and thoracic SPECT images were acquired 72 h after injection of 111 MBq ⁶⁷Ga. We evaluated ¹⁸F-FDG and ⁶⁷Ga uptake visually and semiquantitatively using standardized uptake values (SUVs) and the ratio of lesion to normal lumbar spine (L/N ratio), respectively. The presence of pulmonary and extrapulmonary lesions was evaluated histopathologically or by the radiologic findings. Results: Five patients had only pulmonary lesions, 12 patients had both pulmonary and extrapulmonary lesions, and 1 patient had only an extrapulmonary lesion. Both ⁶⁷Ga planar and SPECT images detected 17 of 21 (81%) clinically observed pulmonary sites. The mean ± SD of the L/N ratio was 1.97 ± 1.09. ⁶⁷Ga planar images detected 15 of 31 (48%) clinically observed extrapulmonary sites. The mean ± SD of the L/N ratio was 1.17 ± 0.33. ¹⁸F-FDG PET detected all 21 (100%) clinically observed pulmonary sites. The mean ± SD of the SUV was 7.40 ± 2.48. ¹⁸F-FDG PET detected 28 of 31 (90%) clinically observed extrapulmonary sites. The mean ± SD of the SUV was 5.90 ± 2.75. Conclusion: The results of this clinical study suggest that ¹⁸F-FDG PET can detect pulmonary lesions to a similar degree as ⁶⁷Ga scintigraphy. However, ¹⁸F-FDG PET appears to be more accurate and contributes to a better evaluation of extrapulmonary involvement in sarcoidosis patients.