Levi C, Gray J E, McCullough E C, Hattery R R
AJR Am J Roentgenol. 1982 Sep;139(3):443-7. doi: 10.2214/ajr.139.3.443.
The use of CT numbers as absolute values was examined by scanning a standard phantom on five CT scanners under a variety of conditions simulating those encountered in routine body CT scanning. The results show that: (1) There are significant differences in absolute CT numbers between most scanners (only one scanner produced CT numbers that were equal to zero for water); (2) There are significant differences in absolute CT numbers between two scanners of the same manufacturer and model that were examined; (3) There is a significant difference in CT numbers in a single phantom scan, dependent on location in the scan, and the format of this variability is not constant from one scanner to another; and (4) There may be a significant difference in absolute CT numbers depending on various physical factors (e.g., kilovoltage, phantom orientation in scan aperture, and position of the phantom in the scan aperture). The findings suggest that there is a wide range of CT numbers observed for a given tissue type as a result of scanner performance alone, and that if absolute CT numbers are to be used for diagnosis the user must document that these machine-related variations are less than the differences thought to be significant.
通过在五台CT扫描仪上扫描标准体模，在模拟常规身体CT扫描中遇到的各种条件下，研究了将CT值用作绝对值的情况。结果表明：（1）大多数扫描仪之间的绝对CT值存在显著差异（只有一台扫描仪产生的水的CT值等于零）；（2）所检查的同一制造商和型号的两台扫描仪之间的绝对CT值存在显著差异；（3）在单个体模扫描中，CT值存在显著差异，这取决于扫描中的位置，并且这种变化的形式在不同扫描仪之间并不恒定；（4）根据各种物理因素（例如千伏、体模在扫描孔径中的方向以及体模在扫描孔径中的位置），绝对CT值可能存在显著差异。研究结果表明，仅由于扫描仪性能，对于给定的组织类型会观察到广泛的CT值范围，并且如果要将绝对CT值用于诊断，用户必须记录这些与机器相关的变化小于被认为具有显著意义的差异。
