Law J
Department of Medical Physics and Medical Engineering, Edinburgh University, UK.
Br J Radiol. 1996 Apr;69(820):306-10. doi: 10.1259/0007-1285-69-820-306.
Maintaining a constant and appropriate mean film optical density in mammography is an essential part of quality assurance in a breast screening programme. It depends on stability in X-ray exposure controls, film supplies, intensifying screens and film processing. A programme of weekly monitoring is described which helps to trace the source of any irregular or step-wise changes in any of the relevant parameters. Its results are also used to investigate by statistical methods the degree of film optical density variation achieved in periods of several weeks of apparent general stability. Results are presented for 20 X-ray sets and a total of 32 record periods of 8-10 weeks each. The mean standard deviation for density of a single film of a Perspex block was found to be 3.5%. For processor speed index it was the same while for X-ray set variations it was less than 2%. Neither of these last two variables showed any strong correlation with block film optical density.
在乳腺钼靶摄影中维持恒定且合适的平均胶片光学密度是乳腺筛查计划质量保证的重要组成部分。这取决于X射线曝光控制、胶片供应、增感屏和胶片冲洗的稳定性。本文描述了一项每周监测计划，该计划有助于追踪任何相关参数中不规则或逐步变化的来源。其结果还用于通过统计方法研究在看似总体稳定的几周时间内所实现的胶片光学密度变化程度。文中给出了20台X射线设备的结果，以及总共32个记录期，每个记录期为8至10周。发现有机玻璃块单张胶片密度的平均标准偏差为3.5%。处理器速度指数的平均标准偏差与之相同，而X射线设备变化的平均标准偏差小于2%。最后这两个变量均与块体胶片光学密度无任何强相关性。
