PET/CT > Artifacts & Pitfalls > Physical Activity

Effect of Physical Exertion on Muscle Activity

22-year-old male with history of Hodgkin's disease treated with chemotherapy. PET/CT ordered for restaging.

Patient had exercised the evening before his PET/CT exam. Due to diffusely increased FDG activity within the musculature, the study was nondiagnostic for confirmation or exclusion of abnormal FDG activity within a residual left supraclavicular lymph nodal mass seen on CT. Repeat PET/CT with patient's having rested the night before confirmed decreased level of intensity of increased FDG activity in the supraclavicular nodal mass (not shown) consistent with some interval response to treatment.

With increasing usage, skeletal muscle relies more on glycolysis to meet the energy demands. Active contraction of skeletal muscle during FDG injection or during the first half-hour following FDG injection will therefore typically result in increased FDG activity in those muscle groups. Intense muscular activity (weight-lifting, heavy exercise, etc.) in the 24 hours preceding injection may also result in increased FDG muscle activity. If a particular set of muscles were used during an activity, increased activity might be limited only to that group of muscles. For example increased uptake can be seen in the pectoral muscles following heavy bench pressing. Increased activity in the secondary muscles of respiration, intercostals muscles and diaphragm, can be seen in patients with pulmonary disease and labored respiration. Altered weight-bearing and muscle-use following surgery or injury can also produce unusual asymmetric patterns of muscular activity. Patients are asked to limit physical activity on the day prior to their examination. Patients are also kept as still as possible in a quiet room during FDG injection, during the post injection waiting period, and during scanning.