Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark.
Department of Radiology, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.
Dentomaxillofac Radiol. 2021 Dec 1;50(8):20200597. doi: 10.1259/dmfr.20200597. Epub 2021 Apr 29.
The aim of this study was to evaluate the effect of field of view (FOV) and beam energy on the scatter-to-primary ratio (SPR) in dental cone-beam CT (CBCT).
An anthropomorphic phantom representing an adult male (ATOM Max 711-HN, Norfolk, VA, USA) was scanned using the 3D Accuitomo 170 CBCT (J. Morita, Kyoto, Japan) using 11 FOVs. During each scan, half of the X-ray beam was blocked. Each scan was performed at three exposure settings with varying beam energy and equal radiation dose: 90 kV 5 mA, 77 kV 7.5 mA and 69 kV 10 mA. The SPR was estimated by measuring the grey values in the blocked and non-blocked regions of the RAW data. The effect of FOV on SPR was evaluated using Dunn's multiple comparison test, and the effect of the exposure settings was compared using a Wilcoxon signed rank test.
Larger FOVs showed increased scatter. FOVs with a shorter isocenter-detector distance showed a particularly high SPR. Most intercomparisons between FOVs were statistically significant. The largest difference was found between 17 × 12 cm and 6 × 6 cm (lower jaw), with the former showing a 4.9-fold higher SPR. The effect of beam energy was relatively small and varied between FOV sizes and positions.
While the choice of FOV size and position is determined by the diagnostic region of interest, the image quality deterioration for large FOVs due to scatter provides another incentive to limit the FOV size as much as possible.
本研究旨在评估视野（FOV）和射线能量对口腔锥形束 CT（CBCT）中散射与原射线比（SPR）的影响。
使用 3D Accuitomo 170 CBCT（日本京都 J.Morita）对代表成年男性的人体模型（ATOM Max 711-HN，美国弗吉尼亚州诺福克）进行扫描，共使用 11 个 FOV。每次扫描时，将一半的 X 射线束阻挡。在三个不同的射线能量和相等辐射剂量的曝光设置下进行每次扫描：90 kV 5 mA、77 kV 7.5 mA 和 69 kV 10 mA。通过测量 RAW 数据中阻挡和非阻挡区域的灰度值来估算 SPR。使用 Dunn 多重比较检验评估 FOV 对 SPR 的影响，使用 Wilcoxon 符号秩检验比较曝光设置的影响。
较大的 FOV 显示出更高的散射。具有较短等中心-探测器距离的 FOV 表现出特别高的 SPR。大多数 FOV 之间的比较具有统计学意义。最大的差异出现在 17×12 cm 和 6×6 cm（下颌）之间，前者的 SPR 高 4.9 倍。射线能量的影响相对较小，且因 FOV 大小和位置而异。
虽然 FOV 大小和位置的选择取决于诊断感兴趣区域，但大 FOV 由于散射导致的图像质量恶化为尽可能限制 FOV 大小提供了另一个激励因素。
