School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW 2650, Australia; Department of Medical Imaging, Faculty of Applied Health Sciences, The Hashemite University, Zarqa 13133, Jordan.
School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW 2650, Australia.
Radiography (Lond). 2022 Aug;28(3):641-647. doi: 10.1016/j.radi.2022.04.011. Epub 2022 May 13.
This experimental study explored the effect of vertical off-centring on computed tomography (CT) numbers in combination with various tube voltages and phantom sizes for two CT units.
CIRS Model 062 Electron Density and system performance phantoms were imaged on Siemens Emotion 16-slice CT and GEMINI-GXL scanners, respectively. Uniformity and accuracy were evaluated as a function of vertical off-centring (20, 40, 60, and 80 mm above the gantry isocentre) using different water phantom sizes (18, 20, and 30 cm) and tube voltages (80, 90, 110, 120, 130 and 140 kVp).
Vertical off-centring and phantom size accounted for 92% of the recorded variance and the resultant change in CT numbers. The uniformity test recorded maximum changes of 14 and 27.2 HU for peripheral ROIs across the X- and Y-axes for an 80 mm phantom shift above the gantry isocentre on the GEMINI GXL and Siemens scanners, respectively. The absolute CT number differences between the superior and inferior ROIs were 13.7 HU for the 30 cm phantom and 4.8 HU for the 20 cm phantom for 80 mm vertical off-centring. The largest differences were observed at lower tube voltages.
It is essential to highlight the significance of CT number variation in clinical decision-making. Phantom off-centring affected the uniformity of these numbers, which were further impacted by the ROI position in this experimental study. CT number variation was more evident in peripheral phantom areas, lower tube voltages and larger phantom sizes.
CT number is observed to be a variable under certain common conditions. This significantly impacts several applications where clinical decisions depend on CT number accuracy for tissue lesion characterisation.
本实验研究探讨了在两种 CT 机上，随着管电压和体模尺寸的变化，垂直偏离中心对 CT 数的影响。
使用 CIRS Model 062 电子密度和系统性能体模，分别在西门子 Emotion 16 层 CT 和 GEMINI-GXL 扫描仪上进行成像。使用不同的水模尺寸（18、20 和 30 cm）和管电压（80、90、110、120、130 和 140 kVp），评估垂直偏离中心（在机架等中心上方 20、40、60 和 80 mm）对均匀性和准确性的影响。
垂直偏离中心和体模尺寸占记录方差和 CT 数变化的 92%。均匀性测试记录到，当体模在 GEMINI GXL 和西门子扫描仪上向上偏离机架等中心 80 mm 时，在 X 和 Y 轴上的外周 ROI 记录到最大的 14 和 27.2 HU 的 CT 数变化。对于 80 mm 的垂直偏离中心，30 cm 体模的上下 ROI 之间的绝对 CT 数差异为 13.7 HU，20 cm 体模的差异为 4.8 HU。在较低的管电压下观察到最大的差异。
在临床决策中强调 CT 数变化的重要性是至关重要的。体模偏离中心影响了这些数值的均匀性，而在本实验研究中，ROI 的位置进一步影响了这些数值的均匀性。在周边体模区域、较低的管电压和较大的体模尺寸下，CT 数的变化更为明显。
在某些常见条件下，CT 数是一个变量。这对几个应用领域产生了重大影响，在这些应用领域中，临床决策依赖于 CT 数的准确性来对组织病变进行特征描述。
