A method for characterization of PhytoPET in plant growth media

A positron emission tomography (PET) system (PhytoPET) designed specifically for plant biology imaging is being developed for use at the Duke University Biology Department Phytotron. The system has a modular design to accommodate various shapes and sizes of plants and plant structures. The target isotope, ¹¹C in ¹¹CO₂ gas, is absorbed by the leaf through photosynthesis then converted to sugars, and translocated to other parts of the plant. A large fraction of positrons from ¹¹C can escape from thin leaves without annihilation, while in the root a large fraction of positrons annihilate because of surrounding materials such as water or soil. Since the PhytoPET system can be used for imaging both leaves and roots, it is required to characterize system performance with various surrounding materials. A capillary tube phantom was designed and fabricated to allow placement within different absorbing media such as air, water, and soil. We report on sensitivity and spatial resolution measurements of the PhytoPET system using this phantom.