*2.2. 18F-FDG PET/CT Scan*

18F-FDG was produced by a GE Medical Cyclotron (Mini trace, GE Healthcare, Milwaukee, WI, USA) and synthesized by the Tracelab MX FDG (GE Healthcare, Milwaukee, WI, USA) automatic synthesis system. The radiochemical purity was more than 95%. All patients were fasting for more than 6 h, with fasting blood glucose ≤ 200 mg/dL before injection. The patients were given an intravenous injection of 18F-FDG 3.70–5.55 MBq/kg according to their body weight. After resting for about 60 min, drinking 200–500 mL of water, and urination, whole-body PET/CT (discovery VCT®, GE Healthcare, Milwaukee, WI, USA) examination was performed. First, 64 slice spiral CT (Discovery VCT®, GE Healthcare, Milwaukee, WI, USA) scanning was performed, operating with tube voltage 110 kV, tube current 110 mA, and layer thickness 3.3 mm. Then, PET imaging was acquired in the three-dimensional acquisition mode, scanning the range from the upper to the middle thigh with 2 min per bed, for a total of 6–7 beds. PET data were reconstructed with the ordered subsets expectation maximization (OSEM) method. The standard reconstruction was performed with a 512 × 512 matrix and 3.3 mm slice thickness. CT data were used for attenuation correction. Finally, cross-sectional, sagittal, coronal CT, PET, and PET/CT fusion images were obtained by the GE AW4.6 workstation software (GE Healthcare, Milwaukee, WI, USA).
