Fluorine-18 Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography Examination and Harmonization Techniques

The participating institutions used different FDG-PET/CT scanner systems: Biograph Duo (Siemens Healthcare), Discovery 600 (GE Healthcare), Gemini TF (Philips Medical Systems), and Gemini GXL (Philips Medical Systems). Before the examination, patients fasted for at least 5 hours, and blood glucose was measured immediately before injection of FDG at 3.0 to 4.0 MBq/kg of body weight. None of the patients had a blood glucose level greater than 200 mg/dL. Approximately 60 minutes after the injection, static emission images were obtained, during which the patients were allowed to breathe normally. The experienced physicians (K.K. and H.K.), who were board certified in both diagnostic radiology and nuclear medicine and who were blinded to the other imaging results or clinical and histopathologic data, retrospectively reviewed all of the FDG-PET/CT images.

Regarding the techniques for FDG-PET/CT harmonization, 3 different harmonization methods were compared using mathematical-based^8,12 and image-based methods. Image-based harmonization was performed using RAVAT (Nihon Medi-Physics Co, Ltd, Tokyo, Japan), which is a commercially available software package that harmonizes SUVs obtained with different PET/CT systems in a range advocated by the Japanese Society of Nuclear Medicine, using phantom data.^16,30 Stand-alone RAVAT software can quantify PET images, and the software is typically used to adjust spatial resolution to harmonize PET images using a 3-dimensional Gaussian filter.