Pulmonary nodules are imaging signs, mainly appearing as round and round-like hyperdense shadows less than 3 cm in diameter, with relatively clear borders to the surrounding lung tissue, and larger than 3 cm in diameter are called pulmonary masses. Pulmonary nodules with a diameter greater than 1 cm and located in the central part of the lung, such as the posterior head of the heart or the lower head of the diaphragm, cannot be detected by chest X-ray. This is beneficial for early detection of the disease. If a nodule in the lung can be missed on a chest X-ray, or if a nodule in a specific area cannot be seen on a chest X-ray, a chest CT should be done.