PHYTO-PET – Imaging plant physiology on a long-axial field-of-view PET scanner

Non-human imaging using either inanimate phantoms or live animal models is sometimes performed as an alternative to human subjects but involve limitations either in fidelity for the former and ethical considerations for the latter. Plant biology has previously been probed using positron emitting tracers, but the potential for long-axial field-of-view (LAFOV) PET/CT systems with higher sensitivities and longer axial coverage in the imaging of plant biology has not yet been explored.

A selection of both ornamental plants and those of agricultural interest were obtained. A method was developed for the safe instillation of radiopharmaceuticals leading to rapid transport kinetics throughout the plant. [¹⁸F]FDG was obtained from an in-house cyclotron and [⁶⁸Ga]Cl₃ from an onsite ⁶⁸Ge/⁶⁸ Ga generator. The potential for LAFOV PET to probe transport kinetics throughout different vascular compartments was assessed, including for plant models which would not fit within the aFOV of a standard short-axial camera.

Several plant models were successfully imaged using both radiopharmaceuticals. Owing to differences in dispersion between [¹⁸F]FDG and [⁶⁸Ga]Cl₃ within the phloem and xylem vascular systems, variation for the in vivo biodistribution was observed between the two radiopharmaceuticals. The transport kinetics were successfully imaged and quantified by means of dynamic imaging and the longer axial coverage lent itself to the imaging of larger plant models, such as Helianthus annuus (Sunflower).

LAFOV PET/CT systems are feasible for both static and dynamic imaging of different plant models. In vivo biodistribution and kinetics were successfully demonstrated. The longer axial coverage enabled efficient imaging of multiple plants or plants which would not have fitted within the axial FOV of a short-axial PET/CT system.