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Development of a small-animal positron emission tomograph with silicon photomultipliers

Final Activity Report Summary - SiPMPETPisa (Development of a small-animal positron emission tomograph with silicon photomultipliers)

The project consisted of the development of a positron emission tomograph (PET) prototype for small animals, such as rats and mice, for preclinical research. The detector heads of the prototype were composed of continuous LYSO scintillator crystals and silicon photomultipliers (SiPMs) as photodetectors. SiPMs were a new type of photodetectors, also known as Geiger-mode avalanche photodiodes (G-APDs), which had very interesting advantages in comparison to other photodetectors, such as high gain, low operating voltage, fast timing properties, compactness, insensitivity to magnetic fields etc. Hence, SiPMs could greatly improve the performance of existing PET scanners.

This photodetector experienced a fast development in the last years. The ‘Centre for Scientific and Technological Research’, FBK-irst, in collaboration with ‘Istituto Nazionale di Fisica Nucleare’ INFN, produced SiPMs for their use in different applications. The application to PET required the development of two-dimensional arrays, i.e. matrices, of SiPMs in a common substrate which minimised the dead area of the photodetector and provided two-dimensional information of the interaction position of the photons in the crystal.

The project included the characterisation and evaluation of the different versions of single SiPMs and SiPM matrices produced at FBK-irst, as well as their test with scintillator crystals for PET applications. The matrices were employed in the development of a PET detector head. Two detector heads, operated in coincidence, constituted the first PET tomograph. The characterisation tests that were performed with the SiPM matrices assessed their good performance and the possibility to employ them for PET applications. A first PET detector head was assembled with the first matrices produced, composed of 16, i.e. four times four, SiPM elements of one times one mm size, coupled to a scintillator crystal. Both pixellated and continuous crystals were tested. The pixellated crystals resulted in a spatial resolution of 20 % FWHM at 511 keV and a spatial resolution of 1 mm given by the crystal pitch. The use of continuous crystals yielded an energy resolution of 14% FWHM at 511 keV and a spatial resolution of 0.6 mm full-width at half maximum (FWHM) using centre-of-gravity algorithms to reconstruct the interaction position of the photons in the crystal. The mechanical setup and readout electronics which were necessary for the development of the first prototype were developed and the prototype was assembled and would be tested shortly after the project completion.