A dedicated high-resolution PET imager for plant sciences.

PET provides an in vivo molecular and functional imaging capability that could be valuable for studying the interaction of plants in changing environments at the whole-plant level. We have developed a dedicated plant PET imager housed in a plant growth chamber (PGC), which provides a fully controlled environment. The system currently contains two types of scintillation detector modules from commercial small animal PET scanners: 84 microPET® detectors, which are made with scintillation crystal arrays of 2.2 mm(3) × 2.2 mm(3) × 10 mm(3) crystals to provide a large detection area; and 32 Inveon™ detectors, which are made with scintillation crystal arrays of 1.5 mm(3) × 1.5 mm(3) × 10 mm(3) crystals to provide higher spatial resolution. The detector modules are configured to form two half-rings, which provide a 15 cm-diameter trans-axial field of view (FOV) for dynamic tomographic imaging of small plants. Alternatively, the Inveon detectors can be reconfigured to form quarter-rings, which provide a 25 cm FOV using step-and-shoot motion. The imager contains two linear stages that move detectors vertically at different heights for multisection scanning, and two rotation stages to collect coincidence events from all angles when using the step-and-shoot acquisition. The detector modules and mechanical components of the imager are housed inside a PGC that regulates the environmental parameters. The system has a typical energy resolution of 15% for the Inveon detectors and 24% for the microPET detectors, timing resolution of 1.8 ns, and sensitivity of 1.3%, 1.4% and 3.0% measured at the center of the FOV, 5 cm off to the larger half-ring and 5 cm off to the smaller half-ring, respectively (with a 350-650 keV energy window and 3.1 ns timing window). The system's spatial resolution is capable of resolving rod sources of 1.25 mm diameter spaced 2.5 mm apart (center to center) using the ML-EM reconstruction algorithm. Preliminary imaging experiments using soybean and wild type and mutant maize labeled with (11)CO2 produced high-quality dynamic PET images that reveal the translocation and distribution patterns of photoassimilates. This system can be used to provide an in vivo molecular and functional imaging capability for plant research.