Acute Infiltrate/Inflammation/Atelectasis

These non-malignant entities are routinely encountered during PET/CT imaging and can be intensely FDG-avid.  

Do not let their intense metabolic activity push you to consider malignancy in your report unless the CT appearance and clinical presentation are suspicious for a pulmonary malignancy.

On the other hand, be cautious about concluding that a large hypermetabolic soft tissue mass is a large pneumonia if the patient does not have the accompanying clinical symptoms of pneumonia.

We generally report (e.g.), “An area of patchy density is noted in the left lower lobe, intensely avid, typically representing an acute infectious/inflammatory process.”

Respiratory motion is a particular imaging problem when evaluating the pulmonary parenchyma.  This is because the patient is typically breathing during the long acquisition time required for PET imaging of the chest (if a normal full inspiratory breath-hold technique is utilized for the CT portion of the exam, marked misregistration will occur). This topic is more fully addressed here.