Department of Radiology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.
J Nucl Med. 2010 Feb;51(2):293-300. doi: 10.2967/jnumed.109.066332. Epub 2010 Jan 15.
PET image quality depends strongly on patient weight and habitus, decreasing for increasing weight and body mass index. Common adult injection rules prescribe either a dose proportional to weight or a fixed dose. In light patients, image quality may improve for decreasing weight more than by inverse proportion. If better quality than in average-adult studies does not justify the associated dose burden, attractive options are to reduce scan time, reduce dose, or any combination of the 2. The objective of this study was to determine quantitative injection rules for pediatric PET allowing clinical implementation of these trade-offs.
Literature methods combining phantom with clinical data were followed to derive patient-specific noise-equivalent count rate density (NECRD) curves as a function of injected dose. From these, it was possible to estimate retrospectively for each patient the scan time that would have been sufficient for the same NECRD as in a 70-kg reference adult; the reduced dose sufficient for constant NECRD and scan time; and a general relationship among scan time, dose, and NECRD. Correlation to the patient statistic giving highest correlation, which was found to be weight, provided rules applicable prospectively. Data from 73 patients (weight, 11.5-91.4 kg; mean, 45.4 kg) were acquired and analyzed.
Following the clinical injection rule, which was proportional to weight, the NECRD increased linearly with decreasing weight. The expression exp[0.019 x (weight [kg] - 70)] for the time reduction possible with the current dose at constant NECRD correlated well with data (R(2) = 0.86). The dose (in MBq) necessary for constant NECRD that should be injected 60 min before imaging is predicted well by 14.8 x exp[0.046 x weight (kg)] (R(2) = 0.88) with the current scan time. A more complex expression to convert NECRD in whole or part to both dose and time savings was also derived. Comparison to common pediatric injection rules showed reasonable agreement with Clark's rule, albeit not at all weights.
Results suggest that pediatric PET of constant image quality (in an NECRD sense) can be performed with time or dose savings, up to 50% for the lightest patients (10-20 kg).
PET 图像质量强烈依赖于患者的体重和体型，体重和体重指数增加会导致图像质量下降。常见的成人注射规则规定剂量与体重成正比或固定剂量。对于较轻的患者，减少体重可能会比按比例减少体重带来更好的图像质量。如果改善后的图像质量不如成人研究中的图像质量，那么减轻剂量负担的方法就变得很有吸引力，例如减少扫描时间、降低剂量或两者的组合。本研究的目的是确定允许临床实施这些权衡的儿科 PET 定量注射规则。
遵循结合体模和临床数据的文献方法，得出患者特异性噪声等效计数率密度（NECRD）曲线，作为注射剂量的函数。由此，可以回顾性地估计每个患者的扫描时间，以便在相同的 NECRD 下与 70 公斤参考成人相同；在保持 NECRD 和扫描时间不变的情况下，减少足够的剂量；以及扫描时间、剂量和 NECRD 之间的一般关系。与患者统计数据相关，相关性最高的是体重，提供了适用于前瞻性的规则。共获得和分析了 73 名患者的数据（体重 11.5-91.4kg；平均体重 45.4kg）。
按照与体重成正比的临床注射规则，NECRD 随体重的降低呈线性增加。用当前剂量在保持 NECRD 不变的情况下减少扫描时间的表达式 exp[0.019 x (体重 [kg] - 70)] 与数据相关性很好（R(2) = 0.86）。在当前扫描时间下，预测注射后 60 分钟内用于保持 NECRD 不变的剂量（以 MBq 为单位），由 14.8 x exp[0.046 x 体重（kg）] 预测得很好（R(2) = 0.88）。还推导出了一个更复杂的表达式，可以将 NECRD 全部或部分转换为剂量和时间节省。与常见的儿科注射规则相比，Clark 规则的结果与该规则合理一致，尽管并非在所有体重都一致。
结果表明，在 NECRD 意义上具有恒定图像质量的儿科 PET 可以通过节省时间或剂量来实现，对于最轻的患者（10-20kg），最多可节省 50%。
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