A pulmonary nodule is a discrete opacity in the lung which may be caused by: 1  Neoplasm: benign or malignant. 2  Granuloma: tuberculosis. 3  Infection: roundish pneumonia. 4  Vascular: infarct, varix, granulomatosis with polyangiitis, rheumatoid arthritis.
1 Helium is also commonly used to pressurize and purge systems of unwanted gases. 2  It is also used in controlled atmospheres when the levels of different gases have to be kept constant. 3  It is used as a protective gas when growing silicon and germanium crystals and when producing titanium and zirconium.
Uses of Helium. 1  The total amount of helium used in the United States grew from about 1.4 billion scf (36 million scm) in 1985 to about 2.6 billion scf (69 million scm) in 1996 and is expected to continue to grow in the foreseeable future (Figure 1.1 showed the trend in helium production and sales from 1960 to 1997).