PET/MR imaging of bone lesions - implications for PET quantification from imperfect attenuation correction
PET/MR imaging of bone lesions - implications for PET quantification from imperfect attenuation correction
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DOI：
10.1007/s00259-012-2113-0
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发表时间：
2012-07-01
影响因子：
9.1
通讯作者：
Kuhn, Felix P.
中科院分区：
文献类型：
--
作者：
Samarin, Andrei;Burger, Cyrill;Kuhn, Felix P.
目的
准确的衰减校正（AC）对于正电子发射断层扫描（PET）示踪剂分布的定量分析至关重要。在磁共振成像（MR）中，皮质骨信号的缺失使得骨分割困难，可能需要采用特殊序列。本研究的目的是评估在基于磁共振的全身PET/MR成像的衰减校正中准确骨分割的必要性。
方法
对22例先后接受PET/CT和3T磁共振成像的患者，通过将代表大部分骨结构的大于100亨氏单位（HU）的值的像素替换为对应软组织的恒定值为36 HU的像素，从而模拟当前基于磁共振的衰减校正图，制作改良的CT衰减校正图。对141个氟脱氧葡萄糖（FDG）阳性骨病变和50个邻近骨的软组织病变进行评估。在使用标准衰减校正图和改良衰减校正图分别重建一次的PET图像中测量每个病变的平均标准化摄取值（SUVmean）。随后，以标准PET图像为参考，计算改良PET图像中病变示踪剂摄取的误差。
结果
在衰减校正图中用软组织值替代骨导致骨病变和邻近骨的软组织病变的示踪剂摄取分别低估11.2±5.4%（范围1.5 - 30.8%）和3.2±1.7%（范围0.2 - 4%）。对脊柱和骨盆骨病变的分析显示误差对病变成分有显著依赖性。对于以硬化为主的脊柱病变，平均低估为15.9±3.4%（范围9.9 - 23.5%），对于溶骨性脊柱病变，平均低估为7.2±1.7%（范围4.9 - 9.3%）。
结论
模拟在PET衰减校正的磁共振图中当前将骨视为软组织的CT数据，导致骨病变中示踪剂摄取被大幅低估，且取决于病变成分，在硬化性病变中误差最大。因此，在磁共振衰减校正图中描绘皮质骨和其他钙化区域对于PET/MR成像中示踪剂摄取值的准确量化是必要的。
Purpose Accurate attenuation correction (AC) is essential for quantitative analysis of PET tracer distribution. In MR, the lack of cortical bone signal makes bone segmentation difficult and may require implementation of special sequences. The purpose of this study was to evaluate the need for accurate bone segmentation in MR-based AC for whole-body PET/MR imaging.Methods In 22 patients undergoing sequential PET/CT and 3-T MR imaging, modified CT AC maps were produced by replacing pixels with values of > 100 HU, representing mostly bone structures, by pixels with a constant value of 36 HU corresponding to soft tissue, thereby simulating current MR-derived AC maps. A total of 141 FDG-positive osseous lesions and 50 soft-tissue lesions adjacent to bones were evaluated. The mean standardized uptake value (SUVmean) was measured in each lesion in PET images reconstructed once using the standard AC maps and once using the modified AC maps. Subsequently, the errors in lesion tracer uptake for the modified PET images were calculated using the standard PET image as a reference.Results Substitution of bone by soft tissue values in AC maps resulted in an underestimation of tracer uptake in osseous and soft tissue lesions adjacent to bones of 11.2 +/- 5.4 % (range 1.5-30.8 %) and 3.2 +/- 1.7 % (range 0.2-4 %), respectively. Analysis of the spine and pelvic osseous lesions revealed a substantial dependence of the error on lesion composition. For predominantly sclerotic spine lesions, the mean underestimation was 15.9 +/- 3.4 % (range 9.9-23.5 %) and for osteolytic spine lesions, 7.2 +/- 1.7 % (range 4.9-9.3 %), respectively.Conclusions CT data simulating treating bone as soft tissue as is currently done in MR maps for PET AC leads to a substantial underestimation of tracer uptake in bone lesions and depends on lesion composition, the largest error being seen in sclerotic lesions. Therefore, depiction of cortical bone and other calcified areas in MR AC maps is necessary for accurate quantification of tracer uptake values in PET/MR imaging.