McKenney Sarah E, Seibert J Anthony, Lamba Ramit, Boone John M
Department of Radiology, University of California Davis Medical Center, Sacramento, California.
Department of Radiology, University of California Davis Medical Center, Sacramento, California.
J Am Coll Radiol. 2014 Mar;11(3):285-91. doi: 10.1016/j.jacr.2013.10.014.
An imaging facility with a diverse fleet of CT scanners faces considerable challenges when propagating CT protocols with consistent image quality and patient dose across scanner makes and models. Although some protocol parameters can comfortably remain constant among scanners (eg, tube voltage, gantry rotation time), the automatic exposure control (AEC) parameter, which selects the overall mA level during tube current modulation, is difficult to match among scanners, especially from different CT manufacturers.
Objective methods for converting tube current modulation protocols among CT scanners were developed. Three CT scanners were investigated, a GE LightSpeed 16 scanner, a GE VCT scanner, and a Siemens Definition AS+ scanner. Translation of the AEC parameters such as noise index and quality reference mAs across CT scanners was specifically investigated. A variable-diameter poly(methyl methacrylate) phantom was imaged on the 3 scanners using a range of AEC parameters for each scanner. The phantom consisted of 5 cylindrical sections with diameters of 13, 16, 20, 25, and 32 cm. The protocol translation scheme was based on matching either the volumetric CT dose index or image noise (in Hounsfield units) between two different CT scanners. A series of analytic fit functions, corresponding to different patient sizes (phantom diameters), were developed from the measured CT data. These functions relate the AEC metric of the reference scanner, the GE LightSpeed 16 in this case, to the AEC metric of a secondary scanner.
When translating protocols between different models of CT scanners (from the GE LightSpeed 16 reference scanner to the GE VCT system), the translation functions were linear. However, a power-law function was necessary to convert the AEC functions of the GE LightSpeed 16 reference scanner to the Siemens Definition AS+ secondary scanner, because of differences in the AEC functionality designed by these two companies.
Protocol translation on the basis of quantitative metrics (volumetric CT dose index or measured image noise) is feasible. Protocol translation has a dependency on patient size, especially between the GE and Siemens systems. Translation schemes that preserve dose levels may not produce identical image quality.
当在不同品牌和型号的CT扫描仪之间传播具有一致图像质量和患者剂量的CT协议时，拥有多种CT扫描仪的成像设备面临着巨大挑战。尽管某些协议参数在不同扫描仪之间可以轻松保持恒定（例如，管电压、机架旋转时间），但在管电流调制期间选择总体毫安水平的自动曝光控制（AEC）参数在不同扫描仪之间很难匹配，尤其是来自不同CT制造商的扫描仪。
开发了在CT扫描仪之间转换管电流调制协议的客观方法。研究了三台CT扫描仪，一台GE LightSpeed 16扫描仪、一台GE VCT扫描仪和一台西门子Definition AS+扫描仪。特别研究了跨CT扫描仪的AEC参数（如噪声指数和质量参考毫安秒）的转换。使用每台扫描仪的一系列AEC参数，在这三台扫描仪上对可变直径的聚甲基丙烯酸甲酯体模进行成像。该体模由5个圆柱形部分组成，直径分别为13、16、20、25和32厘米。协议转换方案基于匹配两台不同CT扫描仪之间的容积CT剂量指数或图像噪声（以亨氏单位计）。从测量的CT数据中开发了一系列对应于不同患者体型（体模直径）的解析拟合函数。这些函数将参考扫描仪（在这种情况下为GE LightSpeed 16）的AEC指标与二级扫描仪的AEC指标相关联。
在不同型号的CT扫描仪之间（从GE LightSpeed 16参考扫描仪到GE VCT系统）转换协议时，转换函数是线性的。然而，由于这两家公司设计的AEC功能存在差异，需要一个幂律函数将GE LightSpeed 16参考扫描仪的AEC函数转换为西门子Definition AS+二级扫描仪的AEC函数。
基于定量指标（容积CT剂量指数或测量的图像噪声）的协议转换是可行的。协议转换取决于患者体型，尤其是在GE和西门子系统之间。保持剂量水平的转换方案可能不会产生相同的图像质量。
