  PET provides in vivo molecular and functional imaging capability that is
crucial to studying the interaction of plant with changing environment at the
whole-plant level. We have developed a dedicated plant PET imager that features
high spatial resolution, housed in a fully controlled environment provided by a
plant growth chamber (PGC). The system currently contains two types of detector
modules: 84 microPET R4 block detectors with 2.2 mm crystals to provide a large
detecting area; and 32 Inveon block detectors with 1.5 mm crystals to provide
higher spatial resolution. Outputs of the four microPET block detectors in a
modular housing are concatenated by a custom printed circuit board to match the
output characteristics of an Inveon detector. All the detectors are read out by
QuickSilver electronics. The detector modules are configured to full rings with
a 15 cm diameter trans-axial field of view (FOV) for dynamic tomographic
imaging of small plants. Potentially, the Inveon detectors can be reconfigured
to quarter-rings to get a 25 cm FOV using step-and-shoot motion. The imager
contains 2 linear stages to position detectors at different heights for
multi-bed scanning, and 2 rotation stages to collect coincidence events from
all angles. The PET system has been built and integrated into the PGC. The
system has a typical energy resolution of 15% for Inveon blocks and 24% for R4
blocks; timing resolution of 1.8 ns; and sensitivity of 1.3%,1.4%,3.0% measured
at center of FOV, 5 cm off to R4 half-ring and 5 cm off to Inveon half-ring,
respectively(with a 350-650 KeV energy and 3.1 ns timing window). System
spatial resolution is similar to that of commercial microPET sytems, with 1.25
mm rod sources in the micro-Derenzo phantom resolved using ML-EM algorithm.
Preliminary imaging experiments using different plants labeled with 11C-CO2
produced high-quality dynamic PET images.
