Comparison of 18F-FDG and 68Ga PET imaging in the assessment of experimental osteomyelitis due to Staphylococcus aureus

Purpose: Although positron emission tomography (PET) using 2-[F-18]fluoro-2-deoxy-D-glucose (F-18-FDG) is a promising imaging modality for bone infections, the technique may still give false-positive results due to unspecific uptake in healing bone. This experimental study compared F-18-FDG and Ga-68 in PET imaging of osteomyelitis and normal bone healing. Methods: A diffuse osteomyelitis model of the tibia was applied in the rat (n=50). Two weeks after operation, PET imaging with F-18-FDG and Ga-68 was performed, followed by peripheral quantitative computed tomography (pQCT) and radiography. Osteomyelitis was verified by quantitative bacteriology. In addition to in vivo imaging, ex vivo measurements of tissue radioactivity were performed to verify uptake of the tracers. Results: Compared with controls with normal bone healing, the osteomyelitic tibias showed increased SUV ratios (i.e. radioactivity ratios between the operated and non-operated sides) for both F-18-FDG (1.74 +/- 0.37) and Ga-68 (1.62 +/- 0.28) (P < 0.001). Ex vivo measurements also showed increased tracer accumulation in the infected bone (P=0.003 for F-18-FDG and P < 0.001 for Ga-68). The intensity of Ga-68 uptake reflected pathological changes of osteomyelitic bones measured by pQCT. The uptake of F-18-FDG, however, did not show as close a correlation with the anatomical changes. The healing bones without infection exhibited slightly elevated uptake of F-18-FDG (SUV ratio 1.16 +/- 0.06), but Ga-68 did not accumulate in the healing bone, as judged on the basis of both in vivo imaging (SUV ratio 1.02 +/- 0.05) and ex vivo measurements (SUV 0.92 +/- 0.21) (P=0.003 and P=0.022 compared with F-18-FDG uptake, respectively). Conclusion: This study suggests the feasibility of Ga-68 PET imaging of bone infections. However, further studies are needed to clarify the value of Ga-68 PET for clinical purposes.