18F-FDG PET/CT imaging
Between January 2008 and January 2014, PET/CT scans were acquired using the dedicated PET/CT system Discovery ST-16 (GE Medical Systems, Milwaukee, WI, USA). Between February 2014 and May 2019, scans were acquired using Biograph mCT.X (Siemens Healthineers, Henkestrasse,Erlangen, Germany), another dedicated PET/CT system. All patients were instructed to fast for at least 6 h before18F-FDG administration. Image acquisition was performed 45–60 min after the intravenous injection of 3.7 MBq/kg18 F-FDG. CT (100 mA, 100 kV, 0.8 s per tube rotation) was used to generate a PET attenuation correction map. The patients were scanned from the skull to the middle of the femur while lying in a supine position.