Discovery 690

FDG was purchased commercially. All FDG-PET images were created using either a 3-dimensional GE Discovery 690 PET/CT scanner or a Siemens ECAT EXACT HR+ PET scanner. Each subject fasted for at least 6 h, resulting in a plasma glucose level less than 120 mg/dl (6.7 mM) at the time of the tracer administration. All patients were injected i.v. with a dose of 142 ± 8 MBq FDG as a slow bolus while sitting quietly in a room with a low noise level and dimmed light. A static emission frame was acquired from 30 to 60 min p.i. for the Siemens ECAT EXACT HR+ PET scanner, respectively from 30 to 45 min p.i. for the Discovery 690 PET/DT. For attenuation correction, a transmission scan with external 68Ge-sources (Siemens) or a low-dose CT was performed before the static acquisition. PET data were reconstructed iteratively (GE) or with filtered back-projection (Siemens).

Radiolabeling and administration of ⁶⁸Ga-PSMA-11 and 18F-PSMA-1007 were performed according to previously reported radiosynthesis and administration procedures [16 (link),17 (link)]. Immediately after injection of the tracer, 20 mg of furosemide was administered intravenously. Patients were asked to empty the bladder prior to the scan. PET/CT scans were acquired 60 min after tracer injection using an iodine-containing contrast agent (Ultravist 300, Bayer Pharma AG, Berlin, Germany; or Imeron 300, Bracco, Konstanz; Germany 2.5 mL/s) during the portal venous phase. For reconstruction, the TrueX algorithm (3 iterations, 21 subsets; Biograph 64, Siemens Healthineers, Erlangen, Germany) or the VUE Point FX algorithm (2 iterations, 36 subsets; Discovery 690) was used with an axial 168 x 168 matrix. Phantom studies based on the National Electrical Manufacturers Association NU2-2001 standard were conducted to allow valid pooling of results between different scanners. Mean injected activity was 213.1 ± 49.7 MBq in pre- and 212.6 ± 45.1 MBq in post-therapeutic PET.

All GEP NET patients underwent [⁶⁸Ga]DOTATOC PET/CT with the same scanner at different institutions (GE Discovery ST, Discovery ST, and Discovery 690; Siemens Biograph Horizon; Philips Gemini GXL 16) before and after complete PRRT for staging and restaging purposes following the current guidelines [22 (link)]. [⁶⁸Ga]DOTATOC PET/CT images were acquired 60 min after an administered [⁶⁸Ga]DOTATOC dose of 2 MBq/kg and co-registered with low-dose CT. The PET scans were validated for proper quantification and quality.