Pozitron Emissziós Tomográfia (PET) olyan nukleáris orvosi képalkotási technika, amely - három dimenziós felvételt készít a test egy kiválasztott részének anatómiájáról és - feltérképezheti az ott lejátszódó funkcionális folyamatokat is.

Típikus PET készülék

PET kép felvétele A koincidenciát feldolgozó egység Szinogram, adat-feldolgozás/tárolás Annihiláció A kép rekonstrukciója

Elektron-pozitron annihiláció (β+ bomlás)

A PET készülék detektor-blokkja és detektor-gyűrűje Fotoelektronsokszorozó (fotomultiplier) Szcintillációs kristályok Detektor-gyűrű Detektor-blokk

How a PET scan is conducted? To conduct the scan, a short-lived radioactive tracer isotope which decays by emitting a positron, and which has been chemically incorporated into a metabolically active molecule, is injected into the living subject (usually into blood circulation). There is a waiting period while the metabolically active molecule (most commonly fluorodeoxyglucose (FDG), a sugar, for which the waiting period is typically an hour) becomes concentrated in tissues of interest; then the subject is placed in the imaging scanner.

Fluorodeoxyglucose (FDG) FDG, as a glucose analog, is taken up by high-glucose-using cells such as brain, kidney, and cancer cells, where phosphorylation prevents the glucose from being released intact. The 2-oxygen in glucose is needed for further glycolysis, so that (in common with 2-deoxy-D-glucose) FDG cannot be further metabolized in cells, and therefore the FDG-6-phosphate formed does not undergo glycolysis before radioactive decay. As a result, the distribution of 18F-FDG is a good reflection of the distribution of glucose uptake and phosphorylation by cells in the body. Before FDG decays, it is inhibited from metabolic degradation or use, because of the fluorine at the 2' position in the molecule. However, after FDG decays radioactively, its fluorine is converted to 18O, and after picking up a H+ from the environment, it becomes glucose-6-phosphate labeled with harmless nonradioactive "heavy oxygen" (oxygen-18) at the 2' position, and is thereafter metabolized normally in the same way as ordinary glucose.

A fluor izotópjai 18O 18F 109.77 perc 1.656 19F 100% Izotóp Természetes előfordulás Bomlási (fél)idő Bomlási mód Bomlási energia (MeV) Bomlási termék 18F Szintetikus rádióaktív izotóp 109.77 perc Elektron befogás 1.656 18O 19F 100% F stabil (10 neutronnal)

Az emberi agy PET képe