Technical Note: Relation between dual-energy subtraction of CT images for electron density calibration and virtual monochromatic imaging
Technical Note: Relation between dual-energy subtraction of CT images for electron density calibration and virtual monochromatic imaging
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技术说明：用于电子密度校准的 CT 图像双能减影与虚拟单色成像之间的关系
DOI：
10.1118/1.4921999
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发表时间：
2015
期刊：
影响因子：
3.8
通讯作者：
Masatoshi Saito
中科院分区：
文献类型：
--
作者：
Watanabe S;Ogino I;Inayama Y;Sugiura M;Sakuma Y;Kokawa A;Kunisaki C;Inoue T;Masatoshi Saito
为了精确校正放射治疗计划中的组织不均匀性，作者先前提出了将能量减去的计算机断层扫描（CT）数转换为电子密度（ΔHU - ρ转换）的简单方法，该方法在较宽的ρ范围内提供ΔHU和ρ之间的单一线性关系。本研究的目的是通过对双能CT的基物质分解进行数值分析，揭示ΔHU图像用于ρ校准与几乎单色CT图像之间的关系。方法通过对国际辐射单位与测量委员会报告‐46人体组织的衰减系数和给定的ρ值进行数值分析，确定ΔHU - ρ转换的权重因子α0。另一个加权因子α(E)，用于从高kV和低kV CT图像合成虚拟单色CT图像，也在0.03 <E< 5 MeV的能量范围内计算，假设皮质骨和水是基础材料。这些材料的质量衰减系数是利用光子截面数据库得到的。选择用于计算衰减的有效x射线能量来模拟工作在80-140和100-140 kV/Sn下的双源CT扫描仪。结果80 ~ 140 kV/Sn的α0测定值为0.455,100 ~ 140 kV/Sn的α0测定值为0.743。这些值与计算的α(E)曲线各自的最大值几乎完全吻合，这些最大值位于大约1 MeV处，其中人体组织中的光子-物质相互作用完全是非相干（康普顿）散射。结论ΔHU图像基本上可以看作是单能量1 - MeV光子获得的CT图像，CT数与电子密度之间存在线性关系。
PurposeFor accurate tissue inhomogeneity correction in radiotherapy treatment planning, the author previously proposed a simple conversion of the energy‐subtracted computed tomography (CT) number to an electron density (ΔHU–ρeconversion), which provides a single linear relationship between ΔHU andρeover a wideρerange. The purpose of the present study was to reveal the relation between the ΔHU image forρecalibration and a virtually monochromatic CT image by performing numerical analyses based on the basis material decomposition in dual‐energy CT.MethodsThe author determined the weighting factor,α0, of the ΔHU–ρeconversion through numerical analyses of the International Commission on Radiation Units and Measurements Report‐46 human body tissues using their attenuation coefficients and givenρevalues. Another weighting factor,α(E), for synthesizing a virtual monochromatic CT image from high‐ and low‐kV CT images, was also calculated in the energy range of 0.03 <E< 5 MeV, assuming that cortical bone and water were the basis materials. The mass attenuation coefficients for these materials were obtained using thexcomphoton cross sections database. The effective x‐ray energies used to calculate the attenuation were chosen to imitate a dual‐source CT scanner operated at 80–140 and 100–140 kV/Sn.ResultsThe determinedα0values were 0.455 for 80–140 kV/Sn and 0.743 for 100–140 kV/Sn. These values coincided almost perfectly with the respective maximal points of the calculatedα(E) curves located at approximately 1 MeV, in which the photon‐matter interaction in human body tissues is exclusively the incoherent (Compton) scattering.ConclusionsThe ΔHU image could be regarded substantially as a CT image acquired with monoenergetic 1‐MeV photons, which provides a linear relationship between CT numbers and electron densities.