CME Nuclear medicine

following intravenous administration of the tracer. Positron-emitters contain an excess of protons in the nucleus which produce a posi-tive electron (positron). Positrons interact with neighbouring electrons in matter to produce paired 511 keV gamma rays (annihi-lation) which travel approximately 180 ° from each other. PET scanners are designed to detect the two gamma rays generated from the annihilation event. They can place the point of emission more accurately than standard single photon nuclear medicine gamma camera imaging, allowing better spa-tial resolution and quantitative accuracy in comparison with SPECT imaging. A com-monly used parameter in clinical PET imaging is the standardised uptake value, a semiquan-titative method to calculate the concentration of radioactivity in a tumour or organ. 18F-fluorodeoxyglucose 18F-fluorodeoxyglucose (18F-FDG) is the most common tracer used in PET imaging for oncological disease. As a glucose ana-logue, it has a similar distribution to glu-cose. Increased glucose metabolism occurs in most cancers due to overexpression of membrane glucose transporters (eg GLUT 1) and high glycolytic enzyme expression and activity (hexokinase).1,2 18F-FDG is phosphorylated by hexoki-nase to 18F-FDG-6-phosphate which does not undergo further metabolism, is trapped and accumulates inside the cell. The half-life of 18F-FDG is approximately 110 min, making it feasible to scan patients at sites distant from the cyclotron from which 18F-FDG is produced. PET/CT in oncolog