Sookpeng S, Martin C J, Krisanachinda A
Department of Radiological Technology, Faculty of Allied Health Sciences, Naresuan University, Phitsanulok, Thailand. Author to whom any correspondence should be addressed.
J Radiol Prot. 2020 Sep;40(3):753-773. doi: 10.1088/1361-6498/ab8a56.
Automatic tube current modulation (ATCM) is now available on all computed tomography (CT) scanners, but there is no standard phantom for testing its operation. For this study, a phantom comprising five elliptical sections of varying diameters in the shape of a pagoda has been made to represent the range of sizes for patients in Thailand and the Far East. ATCM performance can be evaluated in terms of how tube current and image noise vary with changes in the sizes of the sections. Additional rods of different materials with similar properties to human tissues have been inserted to allow the measurement of contrast-to-noise ratios (CNRs) for assessment of image quality. The phantom has been used to test and compare the performance of CT ATCM systems for the major four CT scanner vendors. The results showed that the ATCM systems of Toshiba and GE CT scanners maintained image noise and CNR within narrower ranges by varying tube current aggressively along the scan length, and commencing modulation before the high attenuation sections are reached. In contrast, the ATCM systems of Philips and Siemens scanners adjusted the tube current within narrower ranges, allowed larger variations in image noise and CNR, and commenced modulation at the start of sections with higher attenuation. The phantom can be used to confirm functionality of the system for acceptance testing, as well as providing information on the tradeoff between radiation dose and image quality when setting up clinical protocols during commissioning of new CT scanners. The phantom can also be used on a routine basis to check that performance is maintained, and could be used in the future for selecting protocol settings to give required values of CNR or adjusting protocol settings on different CT scanners to provide similar levels of clinical performance.
目前，所有计算机断层扫描（CT）扫描仪均具备自动管电流调制（ATCM）功能，但尚无用于测试其运行情况的标准体模。在本研究中，制作了一个由五个直径各异的椭圆形截面组成的宝塔形状的体模，以代表泰国和远东地区患者的体型范围。可以根据管电流和图像噪声如何随截面尺寸变化来评估ATCM的性能。已插入具有与人体组织相似特性的不同材料的附加棒条，以便测量对比度噪声比（CNR）来评估图像质量。该体模已用于测试和比较四大CT扫描仪供应商的CT ATCM系统的性能。结果表明，东芝和GE CT扫描仪的ATCM系统通过沿扫描长度大幅改变管电流，并在到达高衰减截面之前开始调制，将图像噪声和CNR保持在较窄范围内。相比之下，飞利浦和西门子扫描仪的ATCM系统在较窄范围内调整管电流，允许图像噪声和CNR有较大变化，并在高衰减截面开始时开始调制。该体模可用于在验收测试中确认系统功能，以及在新CT扫描仪调试期间制定临床方案时提供有关辐射剂量与图像质量之间权衡的信息。该体模还可定期用于检查性能是否保持，并且将来可用于选择协议设置以给出所需的CNR值，或在不同的CT扫描仪上调整协议设置以提供相似水平的临床性能。
