Nagaki Akio, Onoguchi Masahisa, Matsutomo Norikazu
Department of Radiological Technology, Kurashiki Central Hospital, Okayama, Japan.
J Nucl Med Technol. 2011 Jun;39(2):72-6. doi: 10.2967/jnmt.110.081661. Epub 2011 May 12.
The choice of injected dose of (18)F-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.
This study was a retrospective analysis of 76 patients ranging from 29 to 101 kg who were injected with 228-395.2 MBq of (18)F-FDG for PET imaging. The study population was divided into 4 weight-based 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.
The true coincidence rate, random coincidence rate, and NECR significantly increased with increasing injected dose per kilogram (r = 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.
We modified acquisition protocols for (18)F-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.
在获取始终如一的高质量PET图像时，（18）F-FDG注射剂量和采集时间的选择很重要。本研究的目的是确定基于患者体重的三维正硅酸镥PET/CT的最佳采集方案。
本研究对76例体重在29至101千克之间的患者进行回顾性分析，这些患者注射了228 - 395.2MBq的（18）F-FDG进行PET成像。研究人群分为4个基于体重的组：小于45千克（第1组）、45 - 59千克（第2组）、60 - 74千克（第3组）和75千克及以上（第4组）。我们测量了真符合率、随机符合率、噪声等效计数率（NECR）和随机分数，并通过最大肝脏切片中的方差系数（COV）评估图像质量。
每千克注射剂量增加时，真符合率、随机符合率和NECR显著增加（r = 0.91、0.83和0.90；均P < 0.01）。体重过轻患者的NECR在10.11MB/kg时达到最大值。除第3组和第4组外，4组之间的真符合率差异显著（P < 0.01）。第2组与第3组和第4组的真符合率之比分别为1.4和1.6。所有4组的平均随机分数约为35%。4组的COV在所有组对之间均有差异（P < 0.01）。超重患者的COV大于体重过轻患者，超重患者的图像质量较差。
我们根据三维正硅酸镥PET扫描仪的特点和基于患者体重的PET图像质量，修改了（18）F-FDG PET/CT的采集方案。超重患者的最佳采集时间比正常体重患者长约1.4 - 1.6倍。在提高PET图像质量方面，使用真符合率估计最佳采集时间比其他变量更重要。
