适应性统计迭代重建技术降低胸部低剂量CT图像噪声的效果

摘要

目的 探讨适应性统计迭代重建(ASIR)技术降低胸部低剂量CT图像噪声的效果.方法 选取180例接受胸部CT检查的患者随机分为3组,采用自动毫安调节技术行胸部CT扫描.3组预设噪声指数(NI)分别为20、30及40,对每组图像均行ASIR为0、30％、50％及80％重建成4种图像.记录3组的CT剂量指数(CTDIvol)、剂量长度乘积(DLP)并估算有效剂量(ED).由2名医师对图像质量采用5分制进行评估,并用Kappa检验评价观察者间的一致性.结果 3组图像的质量均满足临床诊断要求,观察者间的评估具有一致性(Kappa值为0.485).第一组的CTDIvol为(3.41±1.28)mGy,第二组为(1.40±0.58)mGy,第三组为(0.76±0.46) mGy.第三组的ED降至(0.35±0.20)mSv.第二组ASIR50的图像噪声和第三组的ASIR80比较差异无统计学意义.结论 ASIR技术有助于降低胸部低剂量图像的噪声,在保证诊断图像质量的前提下,ED可降至0.35 mSv.%Objective To evaluate the effect of adaptive statistical iterative reconstruction (ASIR) to decrease CT image noise in the low-dose chest screening. Methods Totally 180 patients who underwent chest screening scan using HDCT with automatic tube current (mA) modulation were categorized randomly into 3 groups. The noise index (NI) for group 1, 2 and 3 was set to 20, 30 and 40, respectively. Images ASIR in each group were reconstructed 0, 30%, 50% and 80%. CT dose index volumes (CTDIvol) and dose length product (DLP) were recorded, while effective dose (ED) was estimated. Image quality was assessed by two radiologists on a 5-points scale. The degree of interobservers concordance was evaluated using Kappa test. Results The images of each group had acceptable image quality, and there was interobserver agreement in diagnosis acceptability (Kappa value was 0. 485). The average CTDIvol for Group 1, 2 and 3 was (3. 41 ±1. 28), (1. 40 ±0. 58) and (0. 76±0. 46)mGy, respectively. ED in Group 3 decreased to (0. 35±0. 20)mSv. There was no statistical difference of image noise between group 2 at ASIR50 and group 3 at ASIR80. Conclusion ASIR helps to reduce low-dose chest CT image noise, and acceptable image quality can be obtained with ED reduced to 0. 35 mSv.