From Ionizing Radiation Detectors For Medical Imaging

8.2 Physics of Positron Emission Tomography

The acquisition of the information required to reconstruct the activity distribution in the patient can be divided into several stages: the positron emission, its annihilation, the interaction of the two annihilation photons in the biological tissue, and their detection.

8.2.1 Positron emission and radionuclides

The positron is the antiparticle of the electron: it is identical to an electron in all of its properties, except that the sign of its electric charge and its magnetic moment is opposite to that of an electron. Positrons are denoted by the symbol e + or more frequently ? +: they can be generated via the decay of several nuclei whose instability is due to an excessive number of protons with respect to the number of neutrons. These kinds of nuclei are inclined to adopt a more stable energetic configuration, by reducing the number of protons through the ? + decay (Fig. 8.4)



Figure 8.4: Diagrams of ? + decay: the nucleus of the ? + source z N is unstable, by having an excessive number of protons with respect to neutrons. The nucleus reaches a more stable and lower energy configuration by reducing the proton number via positron emission; a neutrino is also emitted. The mass balance Q, which represents the released energy, is given by the sum of the kinetic energies of the positron and of the neutrino plus twice the electron rest mass. If the daughter nucleus is created...
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Topics of Interest

8.3 Detection of Annihilation Photon Annihilation photons interact within the detector through Rayleigh, Compton and photoelectric effects: only the latter two release energy to the detector, making...

K.S vegh 1 , T.Marek 2 1 Department of Nuclear Chemistry, E tv s Lor nd University, Budapest, Hungary 2 Research Group for Nuclear Methods in Structural Chemistry, Hungarian Academy of Sciences at E...

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