In terms of FDG activity in the lungs, when is it considered abnormal?

In the context of FDG (fluorodeoxyglucose) PET imaging, assessing lung activity relative to other anatomical structures is crucial for determining the presence of abnormalities, especially malignancy. An FDG uptake in the lungs can be considered abnormal when it exceeds the activity found in mediastinal soft tissue. This is because the mediastinum, which contains vital structures like lymph nodes, heart, and major blood vessels, typically has a baseline FDG activity due to physiological processes.

Elevated FDG uptake in the lung compared to mediastinal soft tissue may suggest the presence of pathological processes such as infection, inflammation, or malignancies, warranting further investigation. In contrast, comparisons to the thoracic cavity, diaphragm, or pulmonary arteries may not provide as specific a reference point for gauging abnormal activity in lung tissues. These structures can exhibit varied FDG uptake based on numerous factors, making them less reliable benchmarks for determining lung abnormalities. Hence, assessing lung FDG activity against mediastinal soft tissue provides a clearer and more clinically relevant context for distinguishing normal from abnormal findings.