Hi, In a chest X- ray, white densities denote involvement of alveoli and small airways. In larger airways, it is darker because of air pockets that is why those are called as air bronchogram. The densities are due to infiltrates. The infiltrates not always indicates infection where there is pus collection. There are other reasons too, such as blood in alveolar hemorrhage, fluid in pulmonary edema and cells in cancer. So, the densities are diagnosed by comparing with other side, with the clinical symptoms and history. Infection is often associated with fever. Likewise history of trauma, smoking history, other malignant conditions, etc lead to diagnose the cause. Discuss with the Doctor about the symptoms and history for further analysis and investigations. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Pradeepraj, General & Family Physician