PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511-keV attenuation coefficients
PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511-keV attenuation coefficients
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DOI：
10.1007/s00259-002-0796-3
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发表时间：
2002-07-01
影响因子：
9.1
通讯作者：
von Schulthess, GK
中科院分区：
文献类型：
--
作者：
Burger, C;Goerres, G;von Schulthess, GK
PET/CT 联合研究中获取的 CT 数据为 PET 发射数据中的光子衰减校正提供了快速且基本无噪声的源。为此，与 40-140 keV 范围内的光子衰减相关的 CT 值必须转换为 511 keV PET 能量下的线性衰减系数。由于衰减取决于光子能量和吸收材料，因此无法设计出准确的理论关系。 Discovery LS PET/CT 扫描仪（GE Medical Systems，密尔沃基，威斯康星州）中实施的转换使用基于水和皮质骨在 CT 和 PET 能量下的衰减的双线性函数。本研究的目的是将这种变换与实验 CT 值和相应的 PET 衰减系数进行比较。通过 68 锗透射扫描计算 14 名患者的定量 PET 衰减图，并生成分辨率匹配的 CT 图像。总共定义了 114 个感兴趣的体积，并测量了平均 PET 衰减系数和 CT 值。根据 CT 值，使用双线性变换计算预测的 PET 衰减系数。当基于511 keV（0.096 cm(-1)）水的窄波束衰减系数进行变换时，软组织中的预测衰减系数高于测量值。通过将变换中的 0.096 cm(-1) 替换为从锗 68 透射扫描中获得的 0.093 cm-1 线性衰减系数，可以减少这种偏差。对校正发射活动的分析表明，所产生的变换本质上相当于人体组织基于传输的衰减校正。然而，对于非人类材料，它可能会分配不准确的衰减系数，这也会影响邻近组织的校正。
The CT data acquired in combined PET/CT studies provide a fast and essentially noiseless source for the correction of photon attenuation in PET emission data. To this end, the CT values relating to attenuation of photons in the range of 40-140 keV must be transformed into linear attenuation coefficients at the PET energy of 511 keV As attenuation depends on photon energy and the absorbing material, an accurate theoretical relation cannot be devised. The transformation implemented in the Discovery LS PET/CT scanner (GE Medical Systems, Milwaukee. Wis.) uses a bilinear function based on the attenuation of water and cortical bone at the CT and PET energies. The purpose of this study was to compare this transformation with experimental CT values and corresponding PET attenuation coefficients. In 14 patients, quantitative PET attenuation maps were calculated from germanium-68 transmission scans, and resolution-matched CT images were generated. A total of 114 volumes of interest were defined and the average PET attenuation coefficients and CT values measured. From the CT values the predicted PET attenuation coefficients were calculated using the bilinear transformation. When the transformation was based on the narrow-beam attenuation coefficient of water at 511 keV (0.096 cm(-1)), the predicted attenuation coefficients were higher in soft tissue than the measured values. This bias was reduced by replacing 0.096 cm(-1) in the transformation by the linear attenuation coefficient of 0.093 cm-1 obtained from germanium-68 transmission scans. An analysis of the corrected emission activities shows that the resulting transformation is essentially equivalent to the transmission-based attenuation correction for human tissue. For non-human material, however, it may assign inaccurate attenuation coefficients which will also affect the correction in neighbouring tissue.