Old lesions are morphologically well-defined and dense, that is, they are very translucent in the lung and the inflated portion of the lung is black. The old foci are gray or white in color, which means that they may be indicative of calcification. For the diagnosis of a stale foci, it should also be combined with a previous medical history. Stale foci are caused by lung diseases such as pneumonia, tuberculosis, and lung abscesses, and when they appear, one should review whether there is a previous history of similar disease. There is also a subset of the population that does not have a clear history of the disease, but also has old tuberculosis foci in the lungs, because there is a subset of the disease that is left in the lungs by its own absorption without clinical symptoms or treatment in a small infection or tuberculosis. Nodules can be ground glass nodules, mixed nodules, or solid nodules, and are judged clinically by their shape and size.