Abstract– While nuclear methods find application in plant
biology there are very limited amount of instrumentation that is
geared to the unique challenges that plant biology presents.
Mostly researchers are utilizing devices created for clinical and
preclinical imaging. The majority of the biologically significant
elements involved in plant formation have positron emitting
isotopes, making positron emission tomography a naturally
fitting imaging modality. One particular caveat in using PET
instrumentation in plant imaging is extremely small thickness of
the leaf as an annihilation medium for emitted positrons. For
positron energies around 1MeV ( as in case of C-11), about 1 mm
of water equivalent material is required for positron conversion,
so most of the positrons would not annihilate inside the leaf,
therefore limiting both sensitivity and spatial resolution of the
imaging system. In this work we made an attempt of determining
whether direct imaging of positrons could be beneficial in plant
biology studies. We compared performance of direct positron
detector with a planar PET system. Detection efficiency ratio of ~
650 in favor of direct positron detection system was measured.
Direct comparison of spatial resolutions yielded comparable
numbers for a setup, when a phantom was placed directly onto
the entrance window of the positron detector. We also
determined quick deterioration of spatial resolution as a function
of source to detector distance. The last observation makes it
necessary to maintain close proximity of the object to the
detector, but this condition can be met in plant biology study.