Javascript er ikke aktivert i din nettleser. Dette er nødvendig for å bruke Oncolex. Kontakt din systemadministrator for å aktivere JavaScript.

Positron Emission Tomography (PET)

Definitions

PET has a very high sensitivity and can register absorption of radiopharmaceutical agents in extremely low concentrations. Since the central atoms in biochemical compounds (carbon, oxygen, nitrogen) all have positron-emitting isotopes that can be produced in small hospital cyclotrons, it is possible to mark a number of central molecules such as oxygen, water, amino acids, various metabolites, hormones, and neurotransmitters.

For clinical PET, dextrose is usually used where a hydroxide group is replaced by 18F (18-flourine), a compound that is called 18F-FDG (flourine-18 labeled deoxyglucose). 18F-FDG has a high affinity for cells with increased metabolism, for example cancer cells. The substance is transported into the cells and phosphorylates glucose to 18F-FDG-phosphate, but no further break-down occurs. Because cell membranes are impermeable to phosphorylated deoxyglucose, an intracellular accumulation of the substance occurs.

Limitations

  • Small tumors ( < 0,5 cm) and tumors with low to moderate absorption can escape detection.
  • Inflammatory conditions will produce increased absorption.
  • For patients with diabetes (especially those requiring insulin) and non-fasting patients, high muscular absorption will reduce the sensitivity for tumor detection.
  • Some tumor types have low FDG absorption (for example, prostate and bronchoalveolar carcinoma).

Sources of error

  • Infections and inflammatory conditions (including post-operative changes) will result in increased absorption.
  • Normally, the intestine can have a high absorption.
  • Myocardium often displays high absorption, also in fasting patients.
  • 18 F-FDG is excreted through the kidneys and FDG in the urinary tract can be misinterpreted.
  •  Absorption in brown fat tissue can be misinterpreted as a tumor if PET is not compared with CT. PET/CT combined in the same apparatus gives better specificity than PET alone.

Equipment

  • PET/CT-scanner  
  • Radio-pharmaceutical agent: 18F-FDG is formed by radiating a heavier natural variant of oxygen with protons. This occurs in a cyclotron. Fluorine-18 (18F) is produced at the hospital cyclotron located at Rikshospitalet .

Oslo University Hospital shall not be liable for any loss whether direct, indirect, incidental or consequential, arising out of access to, use of, or reliance upon any of the content on this website. Oslo University Hospital© 2018