Interstitial pulmonary fibrosis (IPF). Computed tomography (CT) scan of lungs affected by IPF. The two dark structures are the lungs. The white space in the upper centre is the heart. The left lung is the most severely affected, with diseased tissue appearing white. IPF is characterised by progressive thickening and stiffening of the lining of the air sacs in the lungs, causing breathlessness and pain. The cause is often unknown but in some cases the disease is thought to result from an autoimmune disorder. Without treatment IPF can lead to heart failure or bronchopneumonia. Treatment de- pends on the suspected underlying cause. SCIENCE SOURCE / SCIENCE PHOTO LIBRARY.