数字乳腺X线摄影中管电流量与影像质量的关系

目的探讨数字乳腺X线摄影中不同乳腺压迫厚度时管电流量与影像质量的关系。方法全数字乳腺摄影机中采用钼-铑靶滤过组合,对2~7 cm厚度的CDMAM模体选择适宜的管电压,不同管电流量下,进行手动曝光,参数(压迫厚度、管电压、管电流量)设定分别为2 cm、27 kVp、10~90 mAs,3 cm、29 kVp、20~120 mAs,4 cm、29 kVp、20~200 mAs,5 cm、30 kVp、40~220 mAs,6 cm、31 kVp、40~260 mAs和7 cm、32 kVp、80~280 mAs,计算图像影像质量因子(IQF)、对比噪声比(CNR),记录平均腺体剂量(AGD)。通过计算品质因子(FOM),找出各种厚度下最优管电流量及对应的AGD。根据2~7 cm压迫厚度下优化参数表和机器在各种厚度下自动曝光特性,列出2~7 cm厚度下自动曝光参数调整表。同时对不同厚度下IQF、CNR和AGD进行Pearson相关分析,对CNR和管电流量进行曲线拟合。结果在钼-铑靶滤过组合下,不同压迫厚度时,随着管电流量增加,AGD线性增加,FOM先增加后下降或平缓变化。AGD和CNR在2~7 cm厚度下均呈高度正相关,r值均>0.97,P均<0.01。AGD和IQF在2~6 cm时呈高度正相关,r值均>0.87,P均<0.01。参考IQF和FOM因子,不同压迫厚度下,管电压和管电流量适宜匹配参数分别为2 cm、27 kVp、20~30 mAs,3 cm、29 kVp、30~50 mAs,4 cm、29 kVp、80~100 mAs,5 cm、30 kVp、80~120 mAs,6 cm、31 kVp、100~140 mAs,7 cm、32 kVp、80~120 mAs。压迫厚度-自动曝光档的设置对应关系为2 cm-1档、3 cm-2档、4 cm-3档、5 cm-2档、6 cm-0档、7 cm--1档。结论不同乳腺压迫厚度下,具有适宜的管电流量范围,临床实践中应选择相应的自动曝光条件。

A study for tube current exposure time products and image quality in digital mammography

Objective To investigate the relationship between current-exposure time products(mAs)and image quality in digital mammography.Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes using Mo-Rh anode-filer combinations.The exposure parameters were set as follows:(2 cm,27 kVp,10 to 90 mAs);(3 cm,29 kVp,20 to 120 mAs);(4 cm,29 kVp,20 to 200 mAs);(5 cm,30 kVp,40 to 220 mAs);(6 cm,31 kVp,40 to 260 mAs);(7 cm,32 kVp,80 to 280 mAs).The image quality figure(IQF),contrast to noise ratio(CNR),figure of merit(FOM)and the average glandular dose(AGD)were obtained from images.The optimum filtration and kVp for each breast thickness was found from the calculated FOMs.The optimum mAs for each breast thickness were found from the calculated FOMs and IQFs.And the Pearson correlation analysis was used to analyze the correlations among AGD,CNR and IQF.Results With the increase of mAs,the average glandular dose were linearly increased,and the FOM first increased and then decreased or changed slowly.The AGD,CNR and IQF were significantly correlated when the compression thickness was less than 7 cm(r all>0.87,P<0.05).The optimized exposure parameters were list as follows(2 cm,27 kVp,20 to 30 mAs);(3 cm,29 kVp,30 to 50 mAs);(4 cm,29 kVp,80 to 100 mAs);(5 cm,30 kVp,80 to 120 mAs);(6 cm,31 kVp,100 to 140 mAs);(7 cm,32 kVp,80 to 120 mAs).Conclusion The optimum range of mAs can be confirmed with different breast compression thickness and the setting of automatic exposure parameters should be chosen in clinical practice.