Effects of the Obesity Type on FDG-PET Image Quality.

Purpose: The aim of our study is to evaluate whether an ¹⁸ F-FDG PET/CT image quality is influenced by the obesity type visceral fat or subcutaneous fat.
Methods: We chose continuously 68 patients with obesity (35 subcutaneous fats and 33 visceral fats) who underwent an ¹⁸ F-FDG PET/CT scan at our clinic from January 3, 2015 to June 30, 2015. And then, we calculated the noise equivalent count (NEC _density ), the signal to noise ratio of the liver (SNR _liver ), and the ratio of random coincidence counts to total prompt (random/prompt countrate) on each PET/CT image.
Results: We observed that NEC _density was decreased as the body mass index (BMI) and the abdominal circumference increased regardless of the obesity type. When the BMI was on the same degree between two types, however, NEC _density of a visceral fat was 21.6% that is inferior to that of subcutaneous fat on the average. A similar relation was satisfied also in abdominal circumference. Conversely, random/prompt countrate of a visceral fat was more than that of subcutaneous fat when the abdominal circumference and BMI were on the same degree, respectively. Overall, random/prompt countrate tended to increase as BMI and the abdominal circumference increased. With respect to SNR _liver , the value of a visceral fat was inferior to that of subcutaneous fat unconditionally.
Conclusion: When the BMI and abdominal circumference are on the same degree, respectively, the ¹⁸ F-FDG PET/CT image quality of visceral fat is inferior to that of subcutaneous fat. The measure is to extend the collection time by about 20% in the pelvic area from the abdomen of visceral fat type obesity.