微焦点射线机焦点尺寸的刀口工具法定量测试分析

摘要

A method for testing focal spot of a microfocus X-ray machine was put forward,wherein a knife edge tool was used.The magnified image of knife edge tool was acquired and the unsharpness curve was extracted.The unsharpness value was determined by criteria proposed by Klasens and Morgan,and the corresponding focal spot was measured.In addition,the testing results were verified by duplex wire image quality indicator(IQI)and a wedge shaped resolution card.The results show that the relationship between focus size of the microfocus X-ray machine and applied tube current can be described with certain quadratic formulas approximately in the case of a constant tube voltage.Besides,the result from knife edge tool accords with indications from the duplex wire IQI and wedge shaped resolution card.The measuring method by knife edge tool is able to provide reliable result,nevertheless,the criterion to quantitate the corresponding unsharpness curve should be chosen appropriately.Concerning the criterion,Morgan's method is more suitable and reasonable.%为表征微焦点射线机的焦点特性,采用刀口工具法进行了焦点尺寸的测试分析.采集了刀口工具法的放大影像,提取出特定透照条件下的不清晰度曲线,利用Klasens和Morgan定量准则确定了不清晰度数值进而计算出焦点尺寸,并使用双线型像质计、楔形线对卡对焦点尺寸的测试结果进行了验证分析.结果表明,在相同电压下测得的射线机焦点尺寸与管电流间近似符合二次多项式关系,刀口工具法测量结果与双线型像质计、楔形线对卡的图像特征相吻合.基于刀口工具法能可靠地对微焦点射线机的焦点尺寸进行测量,但在分析不清晰度曲线特征时需注意定量准则的适用性,而基于Morgan定量准则能给出更为合理的测量结果.