iDose4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

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。

Investigation impact of dual model iterative reconstruction method（iDose4） on the CT image quality and dose reduction--a phantom approach

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.