The purpose of this study is to see if researchers can improve the detection of lung cancer by using a new method which will help us to take multiple snapshot images of the lungs while the patient is breathing. We are also investigating whether with the help of this new method we can better measure the actual amount of radioactivity that is taken up by the cancer. The name of this new method is respiratory gated PET/CT. Previous research has shown that PET scans may be useful in investigating whether cancer has spread to other parts of the lung or body. Using our standard method, smaller cancers are sometimes difficult to detect in the lungs because the PET images are taken over several minutes and the patient is breathing during that time. That means the cancer may appear "blurred" on the images (like a poor photograph) or may not be identified at all. In this study, in addition to the images that were ordered by your doctor, we will take additional images of your lungs while you are following a breathing command ("breath in-hold-breath out"). We will then compare the images of your cancer during the regular PET study with those taken during the breathing commands.