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Improving resolution without decreasing sensitivity in positron emission tomography (PET) is of great interest for small animal studies. Traditional PET scanners use radially oriented detector block structures. This geometry implies a relationship between the spatial resolution and the sensitivity. An axially oriented crystal geometry can limit this correlation. With a fine measurement of the depth of interaction (DOI) and a continuous measurement of the axial interaction position, this axial geometry can provide high resolution and remove parallax effects. With a careful choice of the crystal and providing enough crystal elements in the radial direction, a good sensitivity can be achieved. Such improvements also allow a more accurate gamma tracking and Compton analysis of the events, indirectly increasing the sensitivity. We have proposed a PET scanner in which LYSO crystals are axially oriented and coupled at both ends by multichannel photo-detectors. The gamma interaction position is given by the hit crystals for the transverse plane and by the light spread on both photo-detectors for the axial direction. The axial position of the events is reconstructed using a calibration procedure and the transverse position is reconstructed using a clustering algorithm. In this paper, we present a complete simulation work flow, including the physical effects, the optical and electronic effects, as well as a reconstruction algorithm. A point sources phantom was used to evaluate the spatial resolutions, and a MOBY phantom was used for overall image quality evaluation. This paper shows that using four modules arranged around the animal, a volumetric spatial resolution below 1 mm3 can be achieved while keeping a detection efficiency close to 10%.
Date of Publication: June 2013