不同曝光模式对数字乳腺X线摄影影像质量和辐射剂量的影响

Influence of different exposure modes on image quality and radiation dose in digital mammography

目的探讨数字乳腺X线摄影中不同曝光模式对影像质量及辐射剂量的影响,便于实际工作中在保证影像质量的前提下,通过对曝光模式及曝光条件选择有效降低病人的辐射损伤。方法先采用自动曝光模式(28kV、60mAs)对乳腺模体进行曝光,然后采用相同的压迫厚度和压力,根据自动曝光模式的摄影条件,在手动曝光模式下,分别固定管电压和管电流量,依次改变相应的管电流量及管电压对模体进行曝光,记录各曝光条件下入射剂量(ESD)、平均腺体剂量(AGD)和美国放射学会(ACR)标准的影像评分值。采用SPSS17.0软件中KruskalWallis检验对自动和手动曝光模式产生的各值进行统计学处理。结果手动曝光模式下,当管电压固定为28kV,管电流量由60mAs升至70mAs时,ESD和AGD分别增加了15.4%;当管电流量降至45mAs时,ESD和AGD分别降低了26.1%。当管电流量固定为60mAs,管电压由28kV升至32kV时,ESD和AGD分别增加了47.0%和62.7%;当管电压降至26kV时,ESD和AGD分别降低了22.6%和28.2%。不同曝光模式下影像的整体质量均无明显差别(P>0.05)。结论自动曝光模式下所得到的ESD与AGD均不是最低剂量。以自动曝光模式为基础,分别固定管电压或管电流量,在一定范围内分别手动降低管电流量或管电压值,在不影响影像质量的前提下,可降低辐射剂量。同时,影像质量达到一定水平后,不再随摄影条件增加而提高。

Objective To evaluate the effect of different exposure modes on radiation dose and image quality in digital mammography, and to explore how to reduce patient＇s radiation injury by choosing proper exposure mode and exposure conditions without sacrifice image quality. Methods A breast phantom was exposed by using automatic exposure mode （60 mAs, 28 kV） and manual exposure modes （37.5 to 70 mAs range, 24 to 32 kV range） respectively. Same oppression thickness and pressure were set for all modes. The averge glandular dose （AGD）, entrance surface dose （ESD）, and image quality score according to American College of Radiology （ACR） criteria were recorded for each image. Kruskal Wallis test was used to compare the image quality scores between automatic and manual modes. All statistic analyses were performed by using SPSS17.0. Results Compared to automatic exposure mode （60 mAs, 28 kV）, the overall score of image quality of manual modes （45 to 70 mAs range, 26 to 32 kV range） had no significant difference. Both ESD and AGD decreased 26.1% and increased 15.4% when the tube loading was changed from 60 mAs to 45 mAs and 70 mAs respectively. The ESD and AGD decreased 22.6%, 28.2% and increased 47.0%, 62.7% when the tube voltage was changed from 28 kV to 26 kV and 32 kV respectively. Conclusion When the image quality reaches to a certain level, it will not be raised by a higher photographic condition. Without sacrifice image quality, the tube loading and tube voltage can be manually decreased to reduce radiation dose.