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Abstract：
Our aim was to define a lower limit of reduced injected activity in delayed [18F]FDG total-body (TB) PET/CT in pediatric oncology patients. Methods: In this single-center prospective study, children were scanned for 20 min with TB PET/CT, 120 min after intravenous administration of a 4.07 ± 0.49 MBq/kg dose of [18F]FDG. Five randomly subsampled low-count reconstructions were generated using ¼, ⅛, [Formula: see text], and [Formula: see text] of the counts in the full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. For the 2 lowest-count reconstructions, smoothing was applied. Background uptake was measured with volumes of interest placed on the ascending aorta, right liver lobe, and third lumbar vertebra body (L3). Tumor lesions were segmented using a 40% isocontour volume-of-interest approach. Signal-to-noise ratio, tumor-to-background ratio, and contrast-to-noise ratio were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale. Results: In total, 113 malignant lesions were identified in 18 patients, who met the inclusion criteria. Of these lesions, 87.6% were quantifiable. Liver SUVmean did not change significantly, whereas a lower signal-to-noise ratio was observed in all low-count reconstructions compared with the reference standard (P < 0.0001) because of higher noise rates. Tumor uptake (SUVmax), tumor-to-background ratio, and total lesion count were significantly lower in the reconstructions with [Formula: see text] and [Formula: see text] of the counts of the reference standard (P < 0.001). Contrast-to-noise ratio and clinical image quality were significantly lower in all low-count reconstructions than with the reference standard. Conclusion: Dose reduction for delayed [18F]FDG TB PET/CT imaging in children is possible without loss of image quality or lesion conspicuity. However, our results indicate that to maintain comparable tumor uptake and lesion conspicuity, PET centers should not reduce the injected [18F]FDG activity below 0.5 MBq/kg when using TB PET/CT in pediatric imaging at 120 min after injection.
摘要：
我们的目的是定义儿科肿瘤患者延迟[18F]FDG全身（TB）PET/CT中注射活性降低的下限。方法：在这项单中心前瞻性研究中，儿童用TBPET/CT扫描20分钟，静脉内施用4.07±0.49MBq/kg剂量的[18F]FDG后120分钟。使用1/4生成了五个随机二次采样的低计数重建，1/8,[公式:见正文],和[公式：见文本]的计数在全剂量列表模式参考标准采集（20分钟），模拟剂量减少。对于2个最低计数的重建，平滑被应用。用置于升主动脉上的感兴趣体积测量背景摄取，肝右叶,和第三腰椎体(L3)。使用40％等高线目标体积方法分割肿瘤病变。信噪比,肿瘤背景比,并计算对比噪声比。三位医生独立识别恶性病变，并使用5点Likert量表评估图像质量。结果：总的来说，在18例患者中发现了113个恶性病变，符合纳入标准的人。在这些病变中，87.6%是可量化的。肝脏SUVmean没有明显变化，而与参考标准相比,在所有低计数重建中观察到较低的信噪比(P<0.0001),原因是较高的噪声率.肿瘤摄取（SUVmax），肿瘤背景比,在使用[公式：见正文]和[公式：见正文]的参考标准的计数重建中，总病变计数显着降低（P<0.001）。在所有低计数重建中，对比噪声比和临床图像质量均显着低于参考标准。结论：儿童延迟[18F]FDGTBPET/CT成像的剂量减少是可能的，而不会损失图像质量或病变的显著性。然而,我们的结果表明，为了保持可比的肿瘤摄取和病变的显著性，当在注射后120分钟在儿科成像中使用TBPET/CT时，PET中心不应将注射的[18F]FDG活性降低至0.5MBq/kg以下。
