Development of novel plastic scintillators based on polyvinyltoluene for the hybrid j-pet/mr tomograph

2. Positron Emission Tomography 
In PET scanners used nowadays in hospitals the ring of inorganic crystal 
scintillators plays a role of detector. In the examination with PET, the patient is 
administered pharmaceutical marker (e.g. 18-fluorodeoxyglucose - FDG) labeled with the 
radioactive isotope decaying by the emission of positron (
β
+
) [1] [2]. The positron 
annihilates with an electron from the body of patient. As a result of annihilation, the mass 
of the positron and electron is converted predominantly into two gamma quanta with 
energy 511 keV each, emitted in opposite directions. This phenomenon is a basis of the 
PET image reconstruction. Hit positions of both gamma quanta on scintillator ring is 
determined and the line of response (LOR) can be marked. Intersection of many lines of 
response allows to determine the annihilation point. A scheme of annihilation and PET 
scanner is shown in Fig 1. 

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8 
Figure 1 The scheme of positron - electron annihilation (left) and PET scanner (right). Figure is adapted from [3]. 
From the PET image, the tracer distribution in the human body can be 
quantitatively determined. The diagnostics is based on different rate of FDG consumption 
in different parts of the body. Cancer or diseased cells have larger metabolism of glucose 
in comparison to healthy tissues. This regions are clearly visible on the PET
image [1] [3] [4] [5]. 
Scanners of positron emission tomography based on inorganic crystals are very 
expensive, mainly because of high price of the scintillators. In Tab. 1 prices per 1 cm
3
of 
three inorganic scintillators that may be used in nowadays PET scanners are given. 
Table 1 Prices of inorganic scintillators possible to use in PET [6]. 
Scintillator