Department of Radiological Technology, School of Health Sciences, Faculty of Medicine, Niigata University, Niigata, 951-8518, Japan.
Med Phys. 2017 Aug;44(8):4179-4187. doi: 10.1002/mp.12386. Epub 2017 Jun 30.
The main objective of this study is to propose an alternative parameterization for the empirical relation between mean excitation energies (I-value) and effective atomic numbers (Z ) of human tissues, and to present a simplified formulation (which we called DEEDZ-SPR) for deriving the stopping power ratio (SPR) from dual-energy (DE) CT data via electron density (ρ ) and Z calibration.
We performed a numerical analysis of this DEEDZ-SPR method for the human-body-equivalent tissues of ICRU Report 46, as objects of interest with unknown SPR and ρ . The attenuation coefficients of these materials were calculated using the XCOM photon cross-sections database. We also applied the DEEDZ-SPR conversion to experimental DECT data available in the literature, which was measured for the tissue-characterization phantom using a dual-source CT scanner at 80 kV and 140 kV/Sn.
It was found that the DEEDZ-SPR conversion enables the calculation of SPR simply by means of the weighted subtraction of an electron-density image and a low- or high-kV CT image. The simulated SPRs were in excellent agreement with the reference values over the SPR range from 0.258 (lung) to 3.638 (bone mineral-hydroxyapatite). The relative deviations from the reference SPR were within ±0.6% for all ICRU-46 human tissues, except for the thyroid that presented a -1.1% deviation. The overall root-mean-square error was 0.21%. Application to experimental DECT data confirmed this agreement within the experimental accuracy, which demonstrates the practical feasibility of the method.
The DEEDZ-SPR conversion method could facilitate the construction of SPR images as accurately as a recent DECT-based calibration procedure of SPR parameterization based directly on the CT numbers in a DECT data set.
本研究的主要目的是提出一种替代的均值激发能量（I 值）与人体组织有效原子数（Z）之间经验关系的参数化方法，并提出一种简化的公式（我们称之为 DEEDZ-SPR），用于通过电子密度（ρ）和 Z 校准从双能（DE）CT 数据中推导出阻止本领比（SPR）。
我们对 ICRU 报告 46 中人体等效组织的这种 DEEDZ-SPR 方法进行了数值分析，作为未知 SPR 和 ρ 的感兴趣对象。这些材料的衰减系数是使用 XCOM 光子截面数据库计算的。我们还将 DEEDZ-SPR 转换应用于文献中可用的实验性 DECT 数据，该数据是使用双源 CT 扫描仪在 80 kV 和 140 kV/Sn 下对组织特性体模进行测量得到的。
结果发现，DEEDZ-SPR 转换可以通过对电子密度图像和低或高千伏 CT 图像进行加权相减来简单地计算 SPR。模拟的 SPR 在 SPR 范围从 0.258（肺）到 3.638（骨矿物质-羟磷灰石）内与参考值非常吻合。除甲状腺外，所有 ICRU-46 人体组织的相对偏差均在参考 SPR 的±0.6%以内，甲状腺的偏差为-1.1%。总体均方根误差为 0.21%。对实验性 DECT 数据的应用证实了该方法在实验精度内的这种一致性，这证明了该方法的实际可行性。
DEEDZ-SPR 转换方法可以像最近基于 DECT 的 SPR 参数化直接基于 DECT 数据集的 CT 数的校准程序一样准确地构建 SPR 图像。
