What is a pet scan? My best friend has been diagnosed with 4 stage lung cancer by a doctor who ...?

had only read a "CT report and biopsy report". We were refered by the general surgeon. We were then told it was inoperatable and he had less than 6 months to live. I thought this was unacceptable because I don't think he had all the information he needed. Am I wrong? We waited in the examining room while he read the report. My friend first had a MRI because he hurt his back.The MRI showed he had "disc degereration and posterial marginal osteophyte disc bulge and spinal c stenoses". He was going to a pain management Dr. but got no relief from the pain, only stayed doped up. We changed Drs, but he has not recieved this report nor saw the MRI. MY firend then had the CT and and showed a growth on his lung. Then the biopsy. They are now scheduleing a PET. I know that biospies can show false positive as well as a CT but what about the PET? Are there any "true" tests? He had none of the signs of lung cancer except weight loss...no coughing, no blood, no pain except his back.