Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, CH-1211 Geneva, Switzerland; University of Technology Sydney, Ultimo NSW 2007, Australia.
University of Technology Sydney, Ultimo NSW 2007, Australia.
Z Med Phys. 2021 Aug;31(3):305-315. doi: 10.1016/j.zemedi.2021.01.006. Epub 2021 Feb 13.
The NEMA NU-2 standard describes a protocol for measurement of scatter fraction (SF) using an axially-aligned line source, offset at 45mm from the central axis, in a cylindrical polyethylene phantom. In this work, which is an extension of our preliminary results previuosly published in the Proceedings of IEEE NSS/MIC 2018 [1], we aim to evaluate the performance of the NEMA NU-2 SF protocol in a Siemens Biograph mCT PET/CT whole-body scanner and a long axial field-of-view (LAFOV) total-body PET scanner to determine whether modifications to the NEMA NU-2 SF protocol are needed for the characterisation of scatter in such scanners. In addition, we evaluate the impact of patient body mass index (BMI) on SF in a LAFOV scanner. The Siemens Biograph mCT and a typical LAFOV PET scanner were modelled in GATE. Monte Carlo simulations were performed to validate the mCT scanner model against published experimental results. SF was estimated using a modified NEMA NU-2 protocol with variable radial offsets on both scanners and compared to ground truth SF measurements obtained with a uniform-activity cylindrical phantom. Correlation between BMI and SF in the LAFOV scanner was evaluated by simulating anthropomorphic phantoms with different BMIs and realistic F-FDG distributions, together with uniformly-filled 200cm long cylindrical phantoms with equivalent effective diameters. The optimal offset was found to be either 60mm or 80mm, depending on the chosen optimality metric. We conclude that modifications to NEMA NU-2 are required for accurate SF characterisation in whole-body and LAFOV scanners. Finally, SF in anthropomorphic phantoms with realistic tissue concentrations of F-FDG was found to be strongly correlated with SF in an equivalent-volume cylindrical phantom for the LAFOV PET scanner; BMI was also found to strongly positively correlate with the SF.
NEMA NU-2 标准描述了一种使用轴向对齐线源在圆柱形聚乙烯体模中测量散射分数 (SF) 的协议，该线源在中心轴上偏移 45mm。在这项工作中，我们旨在评估 NEMA NU-2 SF 协议在 Siemens Biograph mCT PET/CT 全身扫描仪和长轴向视野 (LAFOV) 全身 PET 扫描仪中的性能，以确定是否需要对 NEMA NU-2 SF 协议进行修改，以便在这些扫描仪中对散射进行特征描述。此外，我们还评估了 LAFOV 扫描仪中患者体重指数 (BMI) 对 SF 的影响。Siemens Biograph mCT 和典型的 LAFOV PET 扫描仪在 GATE 中进行建模。进行了蒙特卡罗模拟，以根据已发表的实验结果验证 mCT 扫描仪模型。在这两台扫描仪上使用带有可变径向偏移的修改后的 NEMA NU-2 协议估计 SF，并将其与使用均匀活性圆柱形体模获得的真实 SF 测量值进行比较。通过模拟具有不同 BMI 和真实 F-FDG 分布的人体模型以及具有等效有效直径的均匀填充 200cm 长圆柱形体模，评估了 LAFOV 扫描仪中 BMI 和 SF 之间的相关性。发现最佳偏移量为 60mm 或 80mm，具体取决于所选优化指标。我们得出的结论是，需要对 NEMA NU-2 进行修改，以便在全身和 LAFOV 扫描仪中准确地对 SF 进行特征描述。最后，在 LAFOV PET 扫描仪中，具有真实 F-FDG 组织浓度的人体模型中的 SF 与等效体积圆柱形体模中的 SF 强烈相关；还发现 BMI 与 SF 呈强烈正相关。
