REPLY: Thank you for your comments on our article.
The main message of our study (1) was that only scanning for extended periods of up to 5 min/bed position could maintain the quality of images of heavier patients, whereas an increased 18F-FDG dose of up to 8.8 MBq/kg (similar to the dose usually adopted in the United States and Europe) did not improve image quality, compared with the 3.7 MBq/kg used in Japan. Each study population classified according to body weight criteria was further subcategorized into 3 groups (control, dose-adjusted, and time-adjusted), and the groups did not differ from each other in body mass index (BMI). The heaviest group (>85 kg) showed average BMI values of 31.2–32.2 kg/m2 (classified as obese according to BMI criteria). Thus, it is likely that the choice of parameters (weight vs. BMI) did not largely affect our conclusions.
Our study had one apparent limitation. We could not show data from a subgroup categorized as malignantly obese (BMI > 40). Because the prevalence of patients with a BMI greater than 30 remarkably differs between Japan and the United States (3.2% vs. 30.6% (2)), it was difficult for us to collect such malignantly obese subjects in Japan. However, because random and scatter components increase with patient weight (3), the dose-adjusted approach might be ineffective in malignantly obese subjects. The effects and limitations of the time-adjusted approach for such patients may be clarified in future studies, which we hope will be performed in Western countries.
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