Hyperpolarized 13C-MRSI and PET (hyperPET) in an Osteomyelitis Pig Model: A Pilot Study

AIM: Hyperpolarized 13C-pyruvate magnetic resonance spectroscopic imaging (MRSI) is a real-time metabolic imaging technique, which can be combined with positron emission tomography (PET). In this pilot study, we explore the potential of combined hyperpolarized 13C-MRSI and FDG-PET for imaging of infection. METHODS: Three pigs were inoculated with S. aureusbacteria in the right tibia and saline in the left tibial bone. FDG-PET, 1H-MRI and 13C-MRSI was performed using a clinical whole-body PET/MR system (Siemens Biograph mMR, Erlangen, Germany). Hyperpolarized13C-pyruvate was prepared using a SpinLab System (GE Healthcare, Pittsburgh, PA, USA). 13C-lactate to 13C-pyruvate ratio and FDG SUV was reported in anatomical regions of interest covering bone and regions of inflammation and abscess defined on 1H-MRI. Histopathological examination was performed of both legs. RESULTS: An abscess was observed outside the right (infected bone) on 1H-MRI and confirmed by histopathology. In the abscess the 13C-lactate to 13C-pyruvate ratio was increased as compared to the inflammatory region of the control leg. 18F-FDG uptake showed no clear trend when comparing abscess versus inflammation, but showed an increase considering the infected bone versus the control. In the abscess, the FDG-PET signal distribution had highest intensity in the abscess membrane, whereas the maximum of the13C lactate ratio appears in the abscess cavity. DISCUSSION: The apparent different spatial enhancement pattern of FDG uptake and 13C lactate ratio in abscess suggests that they are independent biomarkers and that hyperpolarized 13C-MRSI is a method with potential for clinical imaging of infection and treatment response.