2-[18F]-FDG PET/CT imaging and interpretation

2-[¹⁸F]-FDG PET/CT scans were performed following the EANM guidelines [25]. All patients underwent 2-[¹⁸F]-FDG PET/CT after at least 6 h of fasting and with blood glucose level lower than 150 mg/dL. An activity of 3.5–4.5 MBq/Kg of radiotracer was administered intravenously and examinations were acquired about 60 ± 10 min after injection from the skull base to the mid-thigh on a Discovery 690 or DST PET/CT tomograph (General Electric Company—GER—Milwaukee, USA) with standard parameters (CT: 80 mA, 120 kV without contrast; 2.5–3.5 min per bed-PET-step of 15 cm); the reconstructions were performed in a 128 × 128 or 256 × 256 matrix and 60 cm field of view.

2-[¹⁸F]-FDG PET/CT were performed during hospitalization for the radiometabolic therapy with 131I to study the FDG-avidity of DTC localizations and compared these findings with the previous or concomitant [131I]WBS.

The PET/CT images were reviewed by two expert nuclear medicine physicians (DA, FB) and every focal tracer uptake different from physiological background and with activity higher than the surrounding tissue was considered as indicative of disease. PET/CT results was compared with a combination of clinical and/or imaging follow-up for at least 6 months taken as reference standard, including cytological reports, histopathologic reports and further imaging studies such as ultrasound, CT with or without contrast, magnetic resonance imaging and/or subsequent PET/CT. In addition, the rising Tg trend over 6 months was accepted as a biochemical indication of disease. Due to the fact that histopathological confirmation of all lesions detected by PET/CT was not ethically and clinically feasible in every patient, the histological confirmation was available in 53 patients where it was warranted.

The mean follow-up time was 44 months (range 2–173 months).