Medicare made an important decision in December 2000 to expand its coverage of fluorodeoxyglucose (FDG) positron-emission tomography (PET) as a cancer screening tool. The agency said it would pay for FDG-PET for diagnosis, staging, and restaging of lung, esophageal, colorectal, lymphoma, melanoma, and head and neck cancers. Previously, Medicare had reimbursed patients for PET for four cancers; however, this only occurred in limited situations. For example, in the case of colorectal cancer, reimbursement occurred only with a recurrence of cancer proven by rising carcinoembryonic antigen levels. Coverage of FDG-PET will be limited to the use of dedicated full-ring and some partial-ring systems. Physicians are expected to order PET scans as a way to avoid major invasive diagnostic procedures.