Discovery st 16 scanner

The patients underwent PET/CT imaging using a GE Discovery ST16 scanner with ¹⁸F‐FDG as the tracer (provided by China Atomic High Tech). The patients fasted for 6 h before the scan and had their blood glucose levels checked (4.5–6.5 mmol/L). They received an intravenous injection of ¹⁸F‐FDG (185–370 MBq) based on their body mass and rested for about an hour before the scan. The scan covered the region from the cranial apex to the mid‐femur, starting with a fluoroscopic acquisition, followed by a CT scan (150 mA, 120 kV), and then a 3D emission acquisition (23 min/bed, matrix 128 × 128). The CT data were used for attenuation correction and reconstructed using ordered subsets expectation maximization (OSEM). The fused images were processed with GE AW workstation software.

Patients were asked to fast for at least 4 h before examination and were required to have a blood glucose level <200 mg/dL. No intravenous contrast enhancement was used. Patients were injected intravenously with 370–555 MBq ¹⁸F-FDG (depending on body weight), and images were acquired 60 min after its administration. Whole-body PET emission scans were obtained from the base of the skull to the midthigh, without position changes. FDG PET/CT was performed on a Discovery ST 16 scanner (GE Healthcare, Milwaukee, WI, USA). Low-dose CT images were used for attenuation correction of PET data. PET images were reconstructed using a CT-based attenuation correction with an ordered-subset expectation maximization iterative reconstruction algorithm (4 iterations and 10 subsets). When these reconstruction parameters were used, the axial spatial resolution of PET at the center of the gantry was 4.80 mm. The scanner underwent 3D normalization well counter correction every three months for optimizing its quantitative accuracy.

The patients were asked to fast for at least 4 h before the examination. Depending on subject’s body weight, 200–444 MBq of [¹⁸F] FDG were injected intravenously. The images were acquired 90 min after the tracer injection. Both PET and low-dose CT covered the skull vertex to the middle thigh. PET was performed on a Biograph mCT scanner (Siemens Medical Solution) or a Discovery ST16 scanner (GE Healthcare), and the images were reconstructed using low-dose CT-based attenuation correction. Each PET scan was acquired with ordered-subset expectation maximization (OSEM) iterative reconstruction algorithm (4 iterations and 10 subsets for the Discovery ST16; 2 iterations and 21 subsets for the Biography mCT). The axial spatial resolutions of PET at the center were 2.16 and 4.80 mm for Biograph mCT and Discovery ST16, respectively. The fusion of low-dose CT and PET images were used for interpretation. The standardized uptake value was calculated according to the following formula: standardized uptake value = radioactivity concentration in tissue [becquerel/gram]/ (injected dose [becquerel]/patient weight [gram]). The maximal standardized uptake value of the primary tumor and metastatic lymph nodes, i.e., SUV_Tumor and SUV_LN, were obtained separately within the volumes-of-interest created manually. The NTR was defined as (SUV_LN / SUV_Tumor).