MODEL RELEASED. Positron emission tomography (PET) scanning. Footage of a radiographer supervising the use of a hospital PET scanner to image a patient. PET scanning involves the injection of a positron-emitting radioactive tracer into the patient. The amount of radioactivity detected from tissues that take up the tracer is used as an indicator of metabolic activity. PET scanning is used to image cancers (malignant tumours), and to diagnose and monitor brain function and diseases such as dementias. This is a Discovery PET scanner from GE Healthcare. Photographed in 2016 at St Thomas' Hospital, London, UK.