管电压对CT值测量、辐射剂量及图像质量影响的模型研究

Influence of tube voltage on CT attenuation, radiation dose, and image quality：phantom study

目的探讨降低管电流和管电压对CT值的影响，及其辐射剂量降低对图像质量的影响程度。方法配置不同浓度对比剂样本共113个，在15种不同扫描条件下进行CT扫描。测量和记录CT值及标准差，分析改变管电流和管电压对CT值测量的影响，并计算对应关系。记录CT容积剂量指数（CTDIvol），计算15种扫描条件下的辐射剂量。不同管电压和管电流下CT值差异比较采用方差分析和Kruskal—Wallis秩和检验，不同管电压下CT值对应关系及管电压和管电流对辐射剂量和图像质量的影响程度分析采用相关性分析。结果管电压固定时不同管电流间（250、200、150、100和50mA）的CT值差异均无统计学意义（F值分别为0．001、0．008、0．075，P均〉0．05）。管电流同定时，不同管电压问（120、100和80kV）的CT值差异均具有统计学意义（H值分别为17．906、17．906、13．527、20．124、23．563，P均〈0．05）。计算不同管电压下同一样本CT值的对应关系：CT值100kv=1．561×CT值120kv＋4．0818，CT值80kv=1．2131×CT值120kv＋0．9283。分析不同管电压下辐射剂量对图像噪声的影响程度，并确立相关性方程：N120kv=-5．9771Ln（D120kv）＋25．412，N100kv=-10．544Ln（D100kv）＋36．262，N80kv=-25．326Ln（D80kv）＋62．816。计算噪声值关键点，证明根据所需图像噪声值（11．2和13．9），可以指导扫描条件，在一定条件下应用低管电压，高管电流可以降低辐射剂量。结论管电压对CT值测量有影响，根据所需图像噪声值调整扫描条件，在一定条件下应用低管电压，高管电流可以降低辐射剂量。改变管电压后造成的CT值变化，可依据不同管电压下CT值对应关系进行校准。

Objective To assess the influence attenuation, radiation dose, and image quality. Methods dilution of contrast medium （370 mg L/ml） was produced. MDCT scan was performed with 15 series of different settings of tube current and tube voltage. CT attenuations with 15 series of different settings were all measured,and influence of tube current and tube voltage on CT attenuations was analyzed. CT dose index （CTDIvol） was recorded. The CT attenuations with different tube voltage and current were compared with one-way ANOVA and Kruskal-Wallis rank sum test. The correlation of CT attenuation with different tube voltage and the influence of tube voltage and current on radiation dose and image quality were tested by correlation analysis. Results Tube current （250,200,150,100, and 50 mA） had no significant effect on CT attenuation （F = 0. 001,0. 008,0. 075, P 〉 0.05 ）, while tube voltage （ 120,100, and 80 kV） had significant effect （H = 17. 906, 17. 906,13. 527,20. 124,23. 563, P 〈 0. 05 ）. The correlation between CT attenuation and tube voltage was determined with equation： CT attenuatio N100 kV = 1. 561 × CT attenuatio NI20Kv ＋ 4. 0818,CT attenuatio N80 kV= 1. 2131× CT attenuatio NI2OKv ＋ 0. 9283. The influence of tube voltage on radiation dose and image quality was also analyzed, and equatious were also obtained： N120kv=-5.9771Ln（D120kv）＋25.412,N100kv=-10.544Ln（D100kv）＋36.262,N80kv=-25.326Ln（D80kv）＋62.816. Aeeording to the resuhs of relationship among CT attenuation, radiation dose, and image quality, lower tube voltage with higher tube eurrent ean reduee the radiation dose. Conclusions Lower tube voltage can reduce the radiation dose. However, CT attenuation was influeneed, and eorreetion should be done with the equations.