Steen W H
J Prosthet Dent. 1984 Mar;51(3):411-8. doi: 10.1016/0022-3913(84)90233-6.
Geometric errors that occur in oblique cephalometric radiographic projections of the edentulous mandible were calculated for different focal-spot-to-object distances (1500, 3000, and 6000 mm). The horizontal errors from tolerance of the porion and nasion fixation in the cephalostat were calculated. The same was done for the vertical errors caused by the variability of the rest position. From the results of this study it can be concluded that the distance between focal spot and object should be as large as possible. It was also found that it is important to minimize the differences in enlargement that may occur on radiograms of different subjects because of changes in the position of the mandible. This position can be standardized by the use of an individual support.
计算了无牙下颌骨斜位头颅侧位X线投影中不同焦点到物体距离（1500、3000和6000毫米）时出现的几何误差。计算了头颅定位仪中听眦点和鼻根点固定公差产生的水平误差。对休息位变化引起的垂直误差也进行了同样的计算。从本研究结果可以得出结论，焦点与物体之间的距离应尽可能大。还发现，尽量减少因下颌骨位置变化而在不同受试者的X线片上可能出现的放大差异很重要。通过使用个体支撑物可以使该位置标准化。
