162 Part II Chapter 6 Figure B. upper panel: Scatter plot of the relation between SBS on planar bone scintigraphy versus TLF on Na[18F]F-PET/CT in each of the patients. The two most extreme outliers between SBS and TLF on Na[18F]F-PET/CT are marked by a red circle. These cases are displayed in the lower panel. Figure B lower panel: patient 6 with FD localizations in multiple ribs (right more than left) and thoracic vertebrae showing severely increased uptake and severe local deformation resulting in low SBS (5.6) due to a low weighing factor of 0.044 for rib involvement but a high TLF (1247 g) as a result of large expansive FD deformities in the ribs with high uptake. Patient 7 suffers McCune-Albright disease with multiple FD localizations with only mildly increased uptake in the right iliac bone, the right proximal femur and in the right tibia, resulting in high SBS (28.9) but low TLF (24.8 g). The low TLF can be largely explained by the relatively low uptake in FD lesions below the cut-off, although the uptake is visually pathological in the pelvis and low extremity. As expected, Na[18F]F-PET/CT showed enhanced spatial resolution over planar bone scintigraphy