Figure 13b. Physiologic thymic uptake in a 23-year-old woman with a history of Hodgkin disease of the chest who was referred for posttherapy evaluation. Axial PET scan (b) demonstrates a unilateral focus of FDG uptake in the superoanterior mediastinum (arrow), a finding that is suspicious for residual disease. Although the uptake is located in the thymic region, its midmediastinal location may suggest viable lymphoma (cf Fig 12). (a, c) Axial CT (a) and PET-CT fusion (c) images help confirm that the anterosuperior mediastinal uptake (arrow) corresponds to thymic tissue, thereby excluding the possibility of residual disease. Although PET-CT is convenient for immediate correlation of images obtained in the same anatomic planes, a recent, separately acquired CT scan would also be helpful in confirming thymic uptake.