Figure 4a. (a) Transaxial (left), coronal (middle), and sagittal (right) 18F-FDG PET scans obtained in a 14-year-old boy with lymphoma involving the right arm demonstrate a triangular area of anterior mediastinal uptake. This area was believed to represent normal thymic uptake on the basis of morphologic features and a maximum SUV of 2.8. The maximum SUV of the mass in the right upper extremity was 15.6. (b) CT scan demonstrates a normal-appearing thymus corresponding to the area of anterior mediastinal uptake seen at 18F-FDG PET.