Patient weight-based acquisition protocols to optimize18F-FDG PET/CT image quality

Abstract

The choice of injected dose of 18F-FDG and acquisition time is important in obtaining consistently high-quality PET images. The aim of this study was to determine the optimal acquisition protocols based on patient weight for 3-dimensional lutetium oxyorthosilicate PET/CT. Methods: This study was a retrospective analysis of 76 patients ranging from 29 to 101 kg who were injected with 228-395.2 MBq of 18F-FDG for PET imaging. The study population was divided into 4 weightbased groups: less than 45 kg (group 1), 45-59 kg (group 2), 60-74 kg (group 3), and 75 kg or more (group 4). We measured the true coincidence rate, random coincidence rate, noise-equivalent counting rate (NECR), and random fraction and evaluated image quality by the coefficient of variance (COV) in the largest liver slices. Results: The true coincidence rate, random coincidence rate, and NECR significantly increased with increasing injected dose per kilogram (r 5 0.91, 0.83, and 0.90; all P < 0.01). NECR maximized at 10.11 MB/kg in underweight patients. The true coincidence rate differed significantly among the 4 groups, except for group 3 versus group 4 (P < 0.01). The ratio of the true coincidence rate for group 2 to groups 3 and 4 was 1.4 and 1.6, respectively. The average random fraction for all 4 groups was approximately 35%. The COV of the 4 groups differed for all pairs (P < 0.01). The COVs in overweight patients were larger than those in underweight patients, and image quality in overweight patients was poor. Conclusion: We modified acquisition protocols for 18F-FDG PET/CT according to the characteristics of a 3-dimensional lutetium orthosilicate PET scanner and PET image quality based on patient weight. The optimal acquisition time was approximately 1.4-1.6 times longer in overweight patients than in normal-weight patients. Estimation of optimal acquisition times using the true coincidence rate is more important than other variables in improving PET image quality. © 2011 by the Society of Nuclear Medicine, Inc.