McCullough E C, Morin R L
AJR Am J Roentgenol. 1983 Jul;141(1):135-40. doi: 10.2214/ajr.141.1.135.
The use of absolute CT numbers for in vivo tissue characterization is compromised by a number of technical and geometrical factors. A phantom simulating thoracic geometry and containing intrapulmonary "features" was scanned on three CT scanners allowing for assessment of CT-number variations with a wide number of scanning and geometric parameters. It was found that, with thoracic geometry, the absolute CT numbers of intrapulmonary features (e.g., solitary pulmonary nodules) can vary significantly due to a number of CT scanning parameters, such as geometry, CT scanner used, and/or time. Such variations must be taken into account when establishing criteria for characterizing tissue types using CT numbers. However, results show that variations in quantitative behavior with reasonable changes in patient geometry do not preclude meaningful characterization of solitary lung nodules (using CT-number averages) using CT scans for the three CT scanners studied, providing CT-number threshold data are derived from the same model scanner and operating conditions. The use of CT-number patterns within high-density intrapulmonary pathology (e.g., solitary pulmonary nodules) is compromised by the fact that high CT-number patterns were found to be a function of the reconstruction filter used and object size as well as being influenced by details of the surrounding medium.
使用绝对CT值进行体内组织特征分析会受到许多技术和几何因素的影响。在三台CT扫描仪上对一个模拟胸部几何形状并包含肺内“特征”的体模进行扫描，以评估在多种扫描和几何参数下CT值的变化。结果发现，对于胸部几何形状，肺内特征（如孤立性肺结节）的绝对CT值会因多种CT扫描参数而有显著变化，这些参数包括几何形状、所使用的CT扫描仪和/或扫描时间。在建立使用CT值表征组织类型的标准时，必须考虑到这种变化。然而，结果表明，在所研究的三台CT扫描仪中，对于患者几何形状的合理变化，定量行为的变化并不妨碍使用CT扫描对孤立性肺结节进行有意义的表征（使用CT值平均值），前提是CT值阈值数据来自同一型号的扫描仪和相同的操作条件。肺内高密度病变（如孤立性肺结节）内CT值模式的使用受到以下因素的影响：已发现高CT值模式是所用重建滤波器、物体大小的函数，并且还受到周围介质细节的影响。
