2.2. F-18 FP-CIT PET/CT and Image Analysis

All the F-18 FP-CIT PET/CT examinations were performed using a Discovery 710 PET/CT (GE Healthcare, Milwaukee, WI, USA) scanner. Patients were intravenously injected with 185 MBq F-18 FP-CIT and PET/CT acquisition was started 180 min after the radiotracer injection. F-18 FP-CIT was supplied by FutureChem in Republic of Korea. A helical CT scan was carried out with a rotation time of 0.5 s at 120 kVp and 100 mAs without an intravenous contrast agent. A PET scan followed immediately and was acquired for 10 min in the three-dimensional mode. All the images were acquired from the skull vertex to the skull base. The patients were allowed to continue their anti-Parkinson medication.

Two experienced nuclear medicine physicians reviewed all the PET/CT images using a dedicated workstation with custom software (Advantage Workstation 5.0). The striatal volumetric analysis was done following a previous study [19]. To analyze the striatal functional volume, a semiautomatically delineated spherical volume-of-interest (VOI) was drawn over each of the two strata (Figure 1). The striatal target volume was segmented with custom software using a gradient-based method that detected the striatal margin based on a change in activity levels near the structure margin automatically [20]. We drew the VOI over the occipital lobe, and the value of the functional striatal volume multiplied by the occipital mean standardized uptake value (SUV mean) was considered nonspecific uptake of the striatum. Specific uptake ratios (SURs) were calculated for the target striatal VOI, and these values were defined as follows: mean standardized uptake value (mean SUV) of striatal VOI − mean SUV of occipital VOI/mean SUV of occipital VOI.

F-18 FP-CIT images of normal scan (a) and abnormal scan (b) groups. The gradient-based VOIs were automatically drawn on the striatum in the PET images.

F-18 FP-CIT PET images were classified into normal and abnormal scans by visual and quantification analysis. First, the visual assessment was done using the morphology and density of the striatum and striatal asymmetry. Second, quantification analysis was performed based on the values of healthy subjects. The SUR cut-off value in the healthy subjects was 2.84. If the visual and quantification analyses showed the same results, the scan results were classified accordingly, while discordant cases were categorized by the agreement of two nuclear medicine physicians.