iDose^4双模型迭代重建算法对CT图像质量及扫描剂量影响的模体研究

Investigation impact of dual model iterative reconstruction method(iDose^4) on the CT image quality and dose reduction—a phantom approach

目的:评价双模型迭代重建算法(iDose4)和滤波反投影算法(FBP)对CT图像质量的影响,探讨应用iDose4降低扫描剂量的潜力。方法:应用256层螺旋CT(Philips Brilliance iCT),在120 kV管电压条件下分别采用200/180/160/140/120/100/80/60/40/20 mAs条件下扫描Catphan模体,采用FBP和iDose4 1~6重建横断图像,以200 mAs FBP重建图像作为参照,分析扫描条件、重建算法对图像质量的影响(CT值、图像噪声、信噪比以及低对比度分辨力),并分析图像质量与扫描剂量的关系。结果:iDose4与FBP重建图像CT值有高度的一致性(P>0.05);iDose4级别1~6重建可以不同程度的降低图像噪声(9.46%~43.30%);在管电流降低至初始值40%~50%时(80~100 mAs),iDose4级别6重建图像与200 mAs FBP重建图像其图像噪声无统计学差异(P>0.05);管电流降低至初始值50%~60%情况下(100~120 mAs),其低对比度分辨力基本维持不变。结论:iDose4可以显著降低图像噪声,提高信噪比,改善图像质量。相对于FBP重建图像,利用iDose4高级迭代重建技术可以在扫描剂量隆低至40%~50%情况下,维持图像质量不变。

Objective： To investigate the impact of iterative reconstruction method （iDose4） on the CT image quality and dose reduction by using phantom studies. Methods： A Catphan phantom was scanned by a 256-slice CT （Philips Brilliance iCT） with varied mAs from 20 to 200, the axial images were reconstructed by filtered back projection （FBP） and iDose4 with a level of 1 to 6. Image quality was assessed with following aspect： CT value accuracy and consistency, image noise and sig- nal-noise-ratio （SNR）, low density resolution. Meanwhile the volume CT dose index CTDIvol and Dose length product DLP were recorded for dose evaluation. Results： The axial image CT values has a high degree of consistency （P〉0.05） for both iDose4 and FBP reconstruction method. The image noise can be reduced in different degree with different iDose4 level 1-6 reconstruction （9.46%-43.30%）. When tube current reduced to 40%-50%（80-100 mAs）, iDose4 level 6 got image without significant difference regarding to the image noise compared to 200 mAs FBP image（P〉0.05）; under the conditions of 50%-60% initial tube current （100-120 mAs）, low density resolution could remain unchanged. Conclusion： iDose4 can significantly reduce image noise and improve image quality, under the condition of 40%-50% scanning dose can get satisfactory image quality. Thus iterative reconstruction has larger space to lower the scanning dose.