Sharifpour Roya, Ghafarian Pardis, Rahmim Arman, Ay Mohammad R
aDepartment of Medical Physics and Biomedical Engineering bResearch Center for Molecular and Cellular Imaging, Tehran University of Medical Sciences cChronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences dPET/CT and Cyclotron Center, Masih Daneshvari Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Departments of eRadiology fElectrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, USA.
Nucl Med Commun. 2017 Nov;38(11):948-955. doi: 10.1097/MNM.0000000000000732.
The aim of this study was to investigate the impact of time-of-flight (TOF) on quantification and reduction of respiratory artifacts.
The National Electrical Manufacturers Association phantom was used for optimization of reconstruction parameters. Twenty seven patients with lesions located in the diaphragmatic region were evaluated. The PET images were retrospectively reconstructed using non-TOF (routine protocol in our department) and TOF algorithms with different reconstruction parameters. Maximum standardized uptake value, estimated maximum tumor diameter, coefficient of variation, signal-to-noise ratio, and lesion-to-background-ratio were also evaluated.
On the basis of phantom experiments, TOF algorithms with two iterations, 18 subsets, and 5.4 mm and 6.4 mm postsmoothing filter reduced the noise by 3.1 and 12.6% in phantom with 2 : 1 activity ratio, and 3.0 and 13.1% in phantom with 4 : 1 activity ratio. The TOF algorithm with two iterations, 18 subsets, and 6.4 mm postsmoothing filter had the highest signal-to-noise value, and was selected as the optimal TOF reconstruction. Mean relative difference for signal-to-noise between non-TOF and optimal TOF in phantom with 2 : 1 and 4 : 1 activity ratio were 11.6 and 18.7%, respectively. In clinical data, the mean relative difference for estimated maximum tumor diameter and maximum standardized uptake value between routine protocol and optimal TOF algorithm were -6.3% (range: -20.4 to -0.6%) and 13.2% (range: 0.3-57.6%), respectively.
Integration of TOF in reconstruction algorithm remarkably improved the white band artifact in the diaphragmatic region. This technique affected the quantification accuracy and resulted in smaller tumor size and higher standardized uptake value in tumors located in/near the diaphragmatic region.
本研究旨在探讨飞行时间（TOF）对呼吸伪影定量及减少的影响。
使用美国国家电气制造商协会体模优化重建参数。对27例病变位于膈肌区域的患者进行评估。PET图像采用非TOF（我们科室的常规方案）和具有不同重建参数的TOF算法进行回顾性重建。还评估了最大标准化摄取值、估计最大肿瘤直径、变异系数、信噪比和病变与背景比值。
基于体模实验，在活性比为2∶1的体模中，迭代次数为2次、子集数为18个、后置平滑滤波器为5.4 mm和6.4 mm的TOF算法分别使噪声降低了3.1%和12.6%；在活性比为 4∶1的体模中，分别降低了3.0%和13.1%。迭代次数为2次、子集数为18个、后置平滑滤波器为6.4 mm的TOF算法具有最高的信噪比，被选为最佳TOF重建。在活性比为2∶1和4∶1的体模中，非TOF与最佳TOF之间信噪比的平均相对差异分别为11.6%和18.7%。在临床数据中，常规方案与最佳TOF算法之间估计最大肿瘤直径和最大标准化摄取值的平均相对差异分别为 -6.3%（范围：-20.4%至 -0.6%）和13.2%（范围：0.3%至57.6%）。
在重建算法中整合TOF可显著改善膈肌区域的白色条带伪影。该技术影响定量准确性，导致位于膈肌区域/附近的肿瘤尺寸更小且标准化摄取值更高。
