It is used in pulmonary disorders to determine Whether lung nodules or mediastinal lymph nodes harbor tumor (metabolic staging) Whether cancer is recurrent in previously irradiated, scarred areas of the lung PET is superior to CT for mediastinal staging because PET can identify tumor in normal-sized lymph nodes and at extrathoracic sites, thereby decreasing the need for invasive procedures such as mediastinoscopy and needle biopsy.