Kinetic Modelling of Infection Tracers [¹⁸F]FDG, [⁶⁸Ga]Ga-Citrate, [¹¹C]Methionine, and [¹¹C]Donepezil in a Porcine Osteomyelitis Model

Introduction. Positron emission tomography (PET) is increasingly applied for infection imaging using [F-18]FDG as tracer, but uptake is unspecific. The present study compares the kinetics of [F-18]FDG and three other PET tracers with relevance for infection imaging. Methods. A juvenile porcine osteomyelitis model was used. Eleven pigs underwent PET/CT with 60-minute dynamic PET imaging of [F-18]FDG, [Ga-68]Ga-citrate, [C-11]methionine, and/or [C-11]donepezil, along with blood sampling. For infectious lesions, kinetic modelling with one- and two-tissue-compartment models was conducted for each tracer. Results. Irreversible uptake was found for [F-18]FDG and [Ga-68]Ga-citrate; reversible uptake was found for [C-11]methionine (two-tissue model) and [C-11]donepezil (one-tissue model). The uptake rate for [Ga-68]Ga-citrate was slow and diffusion-limited. For the other tracers, the uptake rate was primarily determined by perfusion (flow-limited uptake). Net uptake rate for [F-18]FDG and distribution volume for [C-11]methionine were significantly higher for infectious lesions than for correspondingly noninfected tissue. For [C-11]donepezil in pigs, labelled metabolite products appeared to be important for the analysis. Conclusions. The kinetics of the four studied tracers in infection was characterized. For clinical applications, [F-18]FDG remains the first-choice PET tracer. [C-11]methionine may have a potential for detecting soft tissue infections. [Ga-68]Ga-citrate and [C-11]donepezil were not found useful for imaging of osteomyelitis.