McDonald S P
Community Dent Oral Epidemiol. 1984 Jun;12(3):173-6. doi: 10.1111/j.1600-0528.1984.tb01433.x.
Eleven child skulls were radiographed through a range of 50 degrees by varying the horizontal angulation of the X-ray beam in steps of 2 or 5 degrees. The changes in the width of overlapping contact images and the ranges through which no overlap occurred were measured. A linear relationship between changes in X-ray beam angulation and overlap width was found in all the skulls. Using the data it was calculated that for each increase in overlap width of 0.1 mm, 95% of the deviations in X-ray beam angulation were less than 2.5 degrees. The findings of this study suggested that the positioning of the X-ray beam so as to cause no overlapping is at best difficult, and at worst impossible. They also emphasize the importance of using identical projections in estimating the progress of carious lesions on radiographs since small changes can cause overlaps. The use of methods that reduce the error in repositioning the X-ray beam may be important in reducing methodological errors in clinical research.
通过以2度或5度的步长改变X射线束的水平角度，对11个儿童颅骨进行了50度范围的X射线摄影。测量了重叠接触图像宽度的变化以及未发生重叠的范围。在所有颅骨中均发现X射线束角度变化与重叠宽度之间存在线性关系。利用这些数据计算得出，重叠宽度每增加0.1毫米，X射线束角度的95%偏差小于2.5度。本研究结果表明，将X射线束定位成不产生重叠，往好里说是困难的，往坏里说是不可能的。它们还强调了在估计X线片上龋损进展时使用相同投影的重要性，因为微小变化可能导致重叠。采用减少X射线束重新定位误差的方法对于减少临床研究中的方法学误差可能很重要。
