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

Figure 2 Scheme of the simplest unit of J-PET scanner. PM denotes photomultiplier. 
First prototype of J-PET scanner has been already built. Presently it consists of 192 
plastic scintillator strips, each 50 cm long. Thus the axial field of view of the J-PET 
prototype is equal to 50 cm and is few times larger compared to the presently available 
PET scanners based on crystal scintillators [22]. 
In J-PET scanner scintillators are wrapped into reflective and black foils, what 
improves the effectiveness of light detection and ensures light-tightness. The novel scanner 
has a potential of imaging large parts of human body simultaneously. Photographs of
J-PET scanner prototype are shown in Fig. 3.
Figure 3 A front (left) and side (right) view of J-PET scanner prototype 
[23]
. Scintillators wrapped in the black 
foil are placed in the middle. At their both ends vacuum photomultipliers are connected. Photomultipliers are 
placed inside lightproof aluminum housings. 
 

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2.2. Concept of novel J-PET/MR scanner 
J-PET opens new possibilities in the field of diagnostics: allowing e.g. the 
simultaneous examination of the patient using two well established diagnostic methods: 
Positron Emission Tomography and Magnetic Resonance Imaging (MRI). Inventions 
based on this solution are subjects of patent applications [24] [25] [26].
Nowadays, hybrid PET/MR imaging devices are available, allowing simultaneous 
diagnostics with the two techniques. Such scanners are installed in two medical centers in 
Poland. However, the scanners are extremely expensive. Presently used scanners are based 
on inorganic crystals, like in conventional PET. J-PET/MR solution will be built of plastic 
scintillator, what will make the hybrid imaging technology more achievable.
Combining of both devices into a single one enables metabolic and morphological 
imaging during a single examination providing better diagnosis and treatment monitoring. 
This solution helps to eliminate artifacts in tomographic images which hinder identification 
of cancerous lesions. Typically it is possible to carry out exams with this two methods 
sequentially. Patient is positioned differently in PET and MRI scanners, therefore internal 
organs may move involuntary even if the time between both scans is short. In effect, 
alignment of images acquired during such exams is complicated. 
J-PET/MR scanner is also a space and cost saving invention. Moreover, such hybrid 
device reduces radiation dose to which the patient will be exposed by providing both: 
morphological and functional imaging at the same time [27]. Morphological resolution 
achieved with MR is high, therefore combining with PET shows better contrast in soft 
tissues e.g. brain in comparison to hybrid PET/CT examination which is presently 
available [28].
The novel single hybrid device allowing simultaneous examination by PET and 
MRI methods is based on the J-PET concept. It consists of single detection modules built 
of plastic scintillators to which photomultipliers are connected at both ends. Instead of 
vacuum photomultipliers utilized in the first J-PET prototype, silicon ones are used.
Sillicon photomultipliers (SiPMs) are not affected by the magnetic field of MR 
scanner, equal to about 1.5 - 3 Tesla typically, and they do not disturb the homogeneity of 
magnetic field, so they can be utilized in the novel device. 

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J-PET device will be an insert possible to use in existing MR scanners held by 
hospitals without necessity of hardware modification. What is more, combining PET and 
MRI into one device will shorten the time of examination and will have positive impact on 
patient comfort [29].