Axially Oriented Crystal Geometry Applied to Small-Animal PET System: A Proof of Concept

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%.