Royalty free and rights managed images relating to the diagnostic scanning technique of positron emission tomography (PET). This medical procedure uses radioactive tracers to study blood flow and metabolism, often in brain tissue but in other organs as well such as the heart. This section includes molecular model illustrations of the radioactive tracers used. Disorders diagnosed using this technique include some forms of cancer. This technique is also used in research into brain function. Photographs and pictures include PET scanners, radiographers performing scans on patients, and radiologists examining scans to diagnose diseases.