Coincidence planar imaging for dynamic [18F]FDG uptake in nude mice with tumors and inflammation

The Institute of Nuclear Energy Research of Taiwan has developed a dynamic coincidence detection device for positron emitted radiotracer pharmacodynamic study in small mice models. In this study, we set up an experimental paradigm by determining [fluorine-18]-2-deoxy-2-fluoro-D-glucose ([18F]FDG) dynamic uptake in tumors and inflammations in nude mice as the foundation for future applications in therapy development. Histopathology and micro-autoradiography of these tumors and inflammations were obtained for confirmation. Dynamic coincidence planar images of six tumors and two inflammations in nude mice were acquired over 4 hours immediately after injection of 25.9 MBq of [18F]FDG into the right thigh of each animal. After image reconstruction, the lesion-to-background ratios were calculated in regions of interest over the lesion and contralateral thigh to determine the equilibrium status of the radiotracer. All mice were sacrificed for histopathologic examination and six of the mice were examined with micro-autoradiography. [18F]FDG uptake in tumors and inflammations both reached equilibrium about 3 hours after injection. At equilibrium, [ 18F]FDG uptake into tumors was two to four times higher than the background. Uptake into the 4-day and 8-day inflammations was 2.3 and 5.5 times higher than the background, respectively. Histopathology showed macrophage and neutrophil infiltration around the tumors and in the inflammations. Micro-autoradiography showed dense silver grains in the granulation tissue surrounding the tumors and inflammations. The preliminary results suggested that dynamic [18F]FDG coincidence planar imaging can help in determining the suitable time for static [18F]FDG imaging in nude mice models. The optimal time for static [18F]FDG positron emission tomography imaging was around 3 hours after injection. The paradigm for determining a dynamic [18F]FDG uptake pattern was demonstrated for future new therapeutic drug experimental use.