Normally mild to moderate uptake, similar to liver activity, can be seen within the bone marrow. It is commonly seen within the axial (spine, pelvis, sternum, ribs) and proximal appendicular (proximal femurs, humerii) skeleton. This distribution can change with any process that changes normal marrow distribtution or activity. A smooth, diffuse, symmetric pattern of uptake in the proximal skeleton is generally associated with therapy. More careful evaluation is necessary with a history of osseous or marrow involvement. Treated skeletal metastases and subsequent sclerotic bone may produce a heterogeneous pattern of uptake which can be mistaken for metastases.
Common causes for altered marrow distibution/activity: