Detection systems in PET


Posted on Feb 6, 2014

Detection systems are a key component of any imaging system, and an understanding of their properties is important for establishing appropriate operating criteria or designing schemes for obtaining quantitative information. In this section scintillation detection systems, which are used in the majority of PET tomographs, are discussed. The scintil


Detection systems in PET
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lation process involves the conversion of high-energy photons into visible light via interaction with a scintillating material, and consists of the following steps: In a scintillation detector, the scintillator is optically coupled to a photomultiplier tube (PMT) which then generates an electrical signal in response to light incident upon its face. There are several variations on this theme which are used in PET - for example, a 2D array of crystals may be coupled to 4 PMTs (the block-detector, Casey and Nutt, 1986 ), an array of PMTs may be coupled to a single planar crystal (the Anger camera, Anger, 1958 ), or an array of crystals may be coupled to a multi-channel PMT ( Cherry et al 1997 ). Compton scatter and photo-electric absorption generate electrons of differing energy distributions. In photo-electric absorption, all the photon energy is transferred to the electron, and the energy distribution of the photo-electrons is sharply peaked close to the energy of the incident photon. In Compton scatter, the recoil electrons have a range of energies, depending on the scattering angle. From equation 1 we can say that the energy of the recoil electron will be where q is the photon scattering angle, Ebis the energy of the electron, E is the energy of the incident photon and EG­ is the energy of the scattered photon. Ebreaches a maximum when q = p. For 511 keV photons, this value is 340. 7 keV. A typical energy distribution for...




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