摘要目的 分析自适应统计迭代重建算法(ASIR)在腹部CT扫描中对图像质量的影响,探讨其降低辐射剂量的程度.方法 利用Discovery CT 750 HD机型,分别在噪声指数(NI)和ASIR值为10和0(A组)、12和30％(B组)、13和40％(C组)、14和50％(D组)、15和60％(E组)、16和70％(F组)条件下对带有腹环的模体Catphan 500进行扫描,每组扫描3次,每次扫描选取6套图像,每组共18套图像.分析图像的空间分辨率、密度分辨率、CT值的准确性、噪声及辐射剂量.空间分辨率和辐射剂量直接进行比较,密度分辨率、噪声、CT值的准确性用单因素方差分析进行比较.结果 对于空间分辨率,在标准算法下A～F组可分辨的线对数分别为6、6、6、6、6、5 lp/cm,刀锋算法下A～F组可分辨线对数分别为7、7、7、7、7、6 lp/cm.A～F组的噪声分别为(15.23 ±0.18)、(14.58±0.19)、(14.55 ±0.20)、(14.39±0.20)、(14.11±0.24)和(13.60±0.25) HU,组间差异具有统计学意义(F=118.330,P=0.001),密度分辨率的主观评分分别为(3.12±0.64)、(2.89 ±0.60)、(2.78±0.44)、(3.22±0.44)、(2.56±0.53)、(2.44±0.73)分,组间差异具有统计学意义(F=2.548,P=0.040).A～F组的CT容积剂量指数(CTDIvol)值分别为20.99、14.54、12.37、10.67、9.30、8.16 mGy.结论 当NI≤15、ASIR≤60％时,腹部条件下扫描的图像质量没有明显变化,辐射剂量最多可降低约55.7％.当NI值、ASIR值进一步增高时,图像的空间分辨率下降,NI值等于15、ASIR等于60％组图像质量高于其余各组.

abstractsObjective To investigate the effect of adaptive statistical iterative reconstruction (ASIR) on the image quality and radiation dose reduction for abdominal computed tomography (CT) at different noise index (NI) values and ASIR values.Methods The phantom Catphan 500 matched with abdominal ring was scanned by the abdominal CT protocol when NI and ASIR values were 10 and 0 (group A),12 and 30％ (group B),13 and 40％ (group C),14 and 50％ (group D),15 and 60％ (group E),16and 70％ (group F)respectively on the Discovery CT750 HD.The phantom was scanned 3 times repeatedly and 6 set of images were obtained each time,so each group contained 18 set of images.Image spatial resolution and radiation dose were compared directly,and image density resolution,image noise,accuracy of CT values were compared with ANOVA.Results For image spatial resolution,the line pair per centimeter that can be distinguished from group A to group F were 6,6,6,6,6 and 5 lp/cm for images reconstructed with " standard" kernel,which were 7,7,7,7,7 and 6 lp/cm for images reconstructed with " edge"kernel.The difference of objective noise and their deviations [(15.23 ± 0.18),(14.58 ± 0.19),(14.55 ±0.20),(14.39 ± 0.20),(14.11 ± 0.24),(13.60 ± 0.25) HU] and the subjective quality scores (SQS)[(3.12±0.64),(2.89±0.60),(2.78 ±0.44),(3.22±0.44),(2.56±0.53),(2.44±0.73)] for image density resolution from group A to group F were statistically significant (Fnoise =118.330,FSQS =2.548,P ＜ 0.05).The CTDIvol from group A to group F were 20.99,14.54,12.37,10.67,9.30 and 8.16 mGy.Conclusion When NI≤ 15 and ASIR≤ 60％,the image quality can be maintained with 55.7％of radiation dose reduction at most,but the image spatial resolution becomes lower as the values of NI and ASIR become greater.The image quality at NI equal to 15 and the ASIR equal to 60％ is better than any other groups.