Discovery st scanner

All patients fasted for 6 h before ¹⁸F-FDG administration, and the patients’ blood glucose level was checked to ensure it was below 200 mg/dl. PET/CT scans were performed using a Biograph mCT Scanner (Siemens Healthcare, Henkestr, Germany) in 65 patients, and a Discovery ST Scanner (GE Healthcare, Waukesha, USA) in 11 patients. Total body scan was conducted 60 min after the ¹⁸F-FDG injection (0.1 mCi/kg or 3.7 MBq/kg body weight). CT scans of the whole body from skull to mid-thigh were obtained without contrast enhancement in an arm-up position for attenuation correction and fusion (80–200 mAs, 120 kVp, 3 mm slice thickness for the Biograph mCT Scanner; and automatic tube current, 140 kVp, 3.75 mm slice thickness for the Discovery ST Scanner) and were reconstructed in a 512 × 512 matrix. The subsequent PET scan was conducted in six to eight bed positions with acquisition time of 2 to 3 min per bed position. The PET images were reconstructed with a slice thickness of 2 mm for the Biograph mCT Scanner or 3.25mm for the Discovery ST Scanner, using the Ordered Subsets Expectation Maximization (OSEM) iterative reconstruction method. Counter correction and cross-calibration of the two scanners were conducted periodically to ensure an optimal quantitative accuracy, and no significant difference at SUV quantitation was observed between the two scanners.

The patients were required to fast for at least four hours prior to examination. Upon admission, the patients’ body weight was measured and blood glucose level was recorded. Then, 6 MBq/kg of ¹⁸F-FDG (range: 285-460 MBq) was intravenously injected, and PET/CT imaging was performed on the dedicated GE^® Discovery ST Scanner, equipped with PET and eight-slice CT units. Image acquisition was performed with a whole-body field of view (vertex to mid-thigh), 45-60 min after the injection.
CT transmission images for attenuation correction were captured with exposure factors of 120 kVp, 80 mA, and 0.8 s for all examinations; no intravenous CT contrast was administered. Emission PET images were obtained in a two-dimensional mode at the rate of four min per bed position with a three-slice overlap between consecutive bed positions.
Transaxial PET data were reconstructed using filtered back-projection. The CT data for PET were reconstructed to axial slices with a thickness of 3.3 mm. The images were reviewed on GE Advantage Workstation (version 4.2) by two experienced nuclear medicine physicians. Positive uptakes on PET images were based on non-physiological uptakes greater than liver or SUV_max>2.5, corrected for body weight.