1.1 本测试方法涵盖了确定X射线和γ射线计算机断层扫描（CT）系统的密度校准以及使用此信息从CT图像测量材料密度的说明。校准基于对含有已知成分和密度的嵌入样本的材料盘的CT图像的检查。已知标准的测量平均CT值通过图像分析确定，其线性衰减系数通过将其测量的物理密度乘以其公布的质量衰减系数来确定。密度校准通过对数据应用线性回归来执行。一旦校准，图像中未知特征的线性衰减系数可以通过确定其平均CT值来测量。然后，可以从其质量衰减系数或特征的一个代表性知识中提取其密度。 1.2 CT提供了一种极好的非破坏性测量密度变化的方法，否则很难量化密度变化。密度本质上是物质的体积特性。随着测量体积的缩小，局部材料不均匀性变得更加重要；测量值将开始随着材料的体积密度值而变化。 1.3 所有数值均以国际单位制表示。 1.4 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 该测试方法允许使用CT图像数据校准和执行材料密度测量的密度校准程序规范。如果观察到的变化由物体密度的真实变化而不是图像伪影控制，则此类测量可用于评估零件、表征特定系统或比较不同系统。指定程序也可用于确定CT系统的有效X射线能量。 5.2 与基于CT的替代方法相比，推荐的测试方法更准确，更不容易出错，因为它考虑了CT系统的有效能量和X射线衰减过程的能量依赖性影响。 图1 密度校准体模 5.3 该（或任何）测量密度的测试方法仅在观察到的CT数量变化反映物体密度的真实变化而不是图像伪影的情况下有效。 伪影总是在某种程度上存在，并且可以伪装为密度变化。束硬化伪影尤其有害。用户有责任确定或建立密度测量的有效性，或两者兼而有之；也就是说，它们在图像中不受伪影过度影响的区域中执行。 5.4 线性衰减和质量衰减可以用各种方法测量。有关衰减和衰减测量的讨论，请参阅指南 E1441 和实践 E1570 .

1.1 This test method covers instruction for determining the density calibration of X- and γ-ray computed tomography (CT) systems and for using this information to measure material densities from CT images. The calibration is based on an examination of the CT image of a disk of material with embedded specimens of known composition and density. The measured mean CT values of the known standards are determined from an analysis of the image, and their linear attenuation coefficients are determined by multiplying their measured physical density by their published mass attenuation coefficient. The density calibration is performed by applying a linear regression to the data. Once calibrated, the linear attenuation coefficient of an unknown feature in an image can be measured from a determination of its mean CT value. Its density can then be extracted from a knowledge of its mass attenuation coefficient, or one representative of the feature. 1.2 CT provides an excellent method of nondestructively measuring density variations, which would be very difficult to quantify otherwise. Density is inherently a volumetric property of matter. As the measurement volume shrinks, local material inhomogeneities become more important; and measured values will begin to vary about the bulk density value of the material. 1.3 All values are stated in SI units. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This test method allows specification of the density calibration procedures to be used to calibrate and perform material density measurements using CT image data. Such measurements can be used to evaluate parts, characterize a particular system, or compare different systems, provided that observed variations are dominated by true changes in object density rather than by image artifacts. The specified procedure may also be used to determine the effective X-ray energy of a CT system. 5.2 The recommended test method is more accurate and less susceptible to errors than alternative CT-based approaches, because it takes into account the effective energy of the CT system and the energy-dependent effects of the X-ray attenuation process. FIG. 1 Density Calibration Phantom 5.3 This (or any) test method for measuring density is valid only to the extent that observed CT-number variations are reflective of true changes in object density rather than image artifacts. Artifacts are always present at some level and can masquerade as density variations. Beam hardening artifacts are particularly detrimental. It is the responsibility of the user to determine or establish, or both, the validity of the density measurements; that is, they are performed in regions of the image which are not overly influenced by artifacts. 5.4 Linear attenuation and mass attenuation may be measured in various ways. For a discussion of attenuation and attenuation measurement, see Guide E1441 and Practice E1570 .