Chamberlain Reid C, Shindhelm Alexis C, Wang Chu, Fleming Gregory A, Hill Kevin D
Department of Pediatrics, Duke University Medical Center, Durham, NC, USA.
Department of Bioengineering, Duke University Pratt School of Engineering, Durham, NC, USA.
Cardiol Young. 2019 Dec;29(12):1474-1480. doi: 10.1017/S1047951119002506. Epub 2019 Nov 4.
The air gap technique (AGT) is an approach to radiation dose optimisation during fluoroscopy where an "air gap" is used in place of an anti-scatter grid to reduce scatter irradiation. The AGT is effective in adults but remains largely untested in children. Effects are expected to vary depending on patient size and the amount of scatter irradiation produced.
Fluoroscopy and cineangiography were performed using a Phillips Allura Fluoroscope on tissue simulation anthropomorphic phantoms representing a neonate, 5-year-old, and teenager. Monte Carlo simulations were then used to estimate effective radiation dose first using a standard recommended imaging approach and then repeated using the AGT. Objective image quality assessments were performed using an image quality phantom.
Effective radiation doses for the neonate and 5-year-old phantom increased consistently (2-92%) when the AGT was used compared to the standard recommended imaging approaches in which the anti-scatter grid is removed at baseline. In the teenage phantom, the AGT reduced effective doses by 5-59%, with greater dose reductions for imaging across the greater thoracic dimension of lateral projection. The AGT increased geometric magnification but with no detectable change in image blur or contrast differentiation.
The AGT is an effective approach for dose reduction in larger patients, particularly for lateral imaging. Compared to the current dose optimisation guidelines, the technique may be harmful in smaller children where scatter irradiation is minimal.
气隙技术（AGT）是一种在荧光透视期间优化辐射剂量的方法，该方法使用“气隙”代替反散射格栅以减少散射辐射。AGT在成人中有效，但在儿童中基本未经验证。预计效果会因患者体型和产生的散射辐射量而有所不同。
使用飞利浦Allura荧光透视仪对代表新生儿、5岁儿童和青少年的组织模拟人体模型进行荧光透视和血管造影。然后使用蒙特卡罗模拟首先采用标准推荐成像方法估计有效辐射剂量，接着使用AGT重复该操作。使用图像质量模型进行客观图像质量评估。
与基线时去除反散射格栅的标准推荐成像方法相比，当使用AGT时，新生儿和5岁儿童模型的有效辐射剂量持续增加（2% - 92%）。在青少年模型中，AGT使有效剂量降低了5% - 59%，对于侧位投影中更大胸部尺寸的成像，剂量降低幅度更大。AGT增加了几何放大倍数，但图像模糊或对比度差异无明显变化。
AGT是较大患者减少剂量的有效方法，特别是对于侧位成像。与当前的剂量优化指南相比，该技术在散射辐射极少的较小儿童中可能有害。
