Positron-emission tomography (PET) scans of a coronal section through a 63 year old man with diffuse large B-cell lymphoma affecting subdiaphragmatic and splenic lymph node before chemotherapy treatment (left) and tumor regression after 4 chemotherapy sessions (right). The cancer has been highlighted using a radioactive marker in a technique that uses F-18-fluorodeoxyglucose (18F-FDG).