迭代统计重建在CT结肠成像中降低辐射剂量有效性的体模研究

Efficacy of ASIR for reducing radiation dose in CT colonography:a phantom study

目的：评价宝石高分辨CT应用不同水平迭代统计重建法（ASIR）在CT结肠成像中降低辐射剂量的有效性。方法选用一段离体猪结肠通过结扎法获得20个5～10 mm的模拟息肉，运用HRCT在不同扫描条件（120 kVp，10、20、30、40、50及100 mAs）下扫描，其中HRCT分别应用6种不同ASIR水平（0、10%、30%、50%、70%及100%）进行数据重建，获得CT仿真内镜、多平面重建和虚拟分割图像。由两名有经验的放射医师采用盲法对不同采集条件、不同ASIR水平的图像进行客观和主观评价，测量并比较平均噪声、平均信噪比（SNR）及平均对比噪声比（CNR），以及结肠息肉的检出率，利用SPSS 16.0统计软件对每组数据进行方差分析。结果结肠模拟息肉模型研究显示不同管电流时HRCT图像噪声均随应用ASIR水平升高而降低，SNR及CNR随应用ASIR水平升高而增高（P＜0.05）；CT容积剂量指数降低约50%。结论离体模型研究表明在CT结肠成像中，应用ASIR可以显著降低图像噪声，提高信噪比及对比噪声比，从而有效降低辐射剂量。

Objective To evaluate the efficacy of CT colonography with adaptive statistical iterative reconstruction（ASIR）to reduce radiation dose.Methods A series of twenty artificial polyps of 5-10 mm in size were established by ligation in an isolated segment of porcine colon.Volume data were acquired on a High Definition CT scanner at 10,20,30,40,50 and 100 mAs and 120 kVp using six different ASIR levels at 0,10%,30%,50%,70%and 100%.CT virtual endoscopy,multi-planar reformation and virtual dissection models were reconstructed.Two radiologists without knowledge of the polyp location evaluated every image setting. The average noise level,average signal to noise ratio（SNR）and average contrast to noise ratios（CNR）as well as detecting rates of the polyps were calculated and compared statistically among different acquisitions.Results The SNR and CNR progressively increased and the noise decreased with higher percentage of ASIR at every dose level（P〈0.05）.CT dosage index was reduced by 50%. Conclusion ASIR significantly reduces image noise and increases SNR and CNR in low-dose CT colonography with improved image quality and lower CT dosage index.