MODEL RELEASED. PET scan. Nurse talking to a patient about to undergo a positron emission tomography (PET) scan of the brain. This is a technique used to detect areas of abnormal activity in the body. Usually, radioactive glucose is injected into the bloodstream. The PET scanner detects the presence of the glucose in body tissues, and builds up a picture of glucose concentration, and thus metabolic activity, in the scanned area. This is particularly useful in detecting brain tumours, which show a marked difference in activity to healthy brain tissue. Here, the scan is to be used to find where a biopsy of brain tumour tissue can be taken from.