Methodological accuracy of image-based electron density assessment using dual-energy computed tomography
Methodological accuracy of image-based electron density assessment using dual-energy computed tomography
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DOI：
10.1002/mp.12265
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发表时间：
2017-06-01
期刊：
影响因子：
3.8
通讯作者：
Greilich, Steffen
中科院分区：
文献类型：
--
作者：
Moehler, Christian;Wohlfahrt, Patrick;Greilich, Steffen
目的：电子密度是影响放疗患者光子和离子剂量分布的最重要组织特性。双能计算机断层扫描（DECT）通过结合在两个不同的有效x射线能谱上获得的光子衰减信息来确定电子密度。目前提出的算法大多使用图像重建后提供的CT数作为输入参数，即基于图像。为了探索这些方法可以达到的精度，我们量化了看似最简单的方法的内在方法和校准不确定度。方法：在研究的方法中，电子密度是用两个DECT图像的单参数线性叠加（“alpha混合”）计算的，这相当于两个x射线能谱的光子衰减截面之间的仿射关系。我们建议使用后一种关系进行光谱相关混合参数的经验校准。为了对电子密度不确定度进行结论性评估，我们选择从ct相关的影响（如噪声和束硬化）中分离出纯粹的方法学不确定度成分。结果：分析计算的谱加权衰减系数，我们发现所研究的方法普遍适用于人体组织的任意混合物，方法不确定度的上限为0.2%，不包括高z元素，如碘。建议的校准程序是无偏差的，使用标准设备可以直接执行。在五个已发表的数据集上测试校准，尽管使用了不同的实验设置和CT协议，但我们在校准结果中获得了非常小的差异。因此，可以设想采用每个扫描仪类型和电压组合的一般校准。结论：考虑到阿尔法混合方法在临床应用中的高度适用性以及非常小的方法不确定性，我们得出结论，进一步改进基于图像的电子密度评估的ect算法是不可取的。(C) 2017年美国医学物理学家协会
Purpose: Electron density is the most important tissue property influencing photon and ion dose distributions in radiotherapy patients. Dual-energy computed tomography (DECT) enables the determination of electron density by combining the information on photon attenuation obtained at two different effective x-ray energy spectra. Most algorithms suggested so far use the CT numbers provided after image reconstruction as input parameters, i. e., are imaged-based. To explore the accuracy that can be achieved with these approaches, we quantify the intrinsic methodological and calibration uncertainty of the seemingly simplest approach.Methods: In the studied approach, electron density is calculated with a one-parametric linear superposition ('alpha blending') of the two DECT images, which is shown to be equivalent to an affine relation between the photon attenuation cross sections of the two x-ray energy spectra. We propose to use the latter relation for empirical calibration of the spectrum-dependent blending parameter. For a conclusive assessment of the electron density uncertainty, we chose to isolate the purely methodological uncertainty component from CT-related effects such as noise and beam hardening.Results: Analyzing calculated spectrally weighted attenuation coefficients, we find universal applicability of the investigated approach to arbitrary mixtures of human tissue with an upper limit of the methodological uncertainty component of 0.2%, excluding high-Z elements such as iodine. The proposed calibration procedure is bias-free and straightforward to perform using standard equipment. Testing the calibration on five published data sets, we obtain very small differences in the calibration result in spite of different experimental setups and CT protocols used. Employing a general calibration per scanner type and voltage combination is thus conceivable.Conclusion: Given the high suitability for clinical application of the alpha-blending approach in combination with a very small methodological uncertainty, we conclude that further refinement of image-based DECT-algorithms for electron density assessment is not advisable. (C) 2017 American Association of Physicists in Medicine