多排螺旋CT纵轴分辨力和图像噪声影响因素研究

目的研究多排螺旋CT不同成像参数对图像噪声、纵（Z）轴分辨率或断层灵敏度曲线（SSP）的影响,确定多排螺旋CT成像质量影响因素及其优化匹配关系。方法采用标准头部和腹部扫描条件,选取不同的重建层厚、准直器宽度、螺距、卷积重建算法对不同测试体模进行扫描,比较不同参数对断层灵敏度曲线和图像噪声的影响。结果①SSP测试结果：当螺距和重建层厚保持不变,使用三种卷积重建算法重建测量得到的SSP曲线的半高宽（FWHM）,即有效层厚基本保持不变。对于相同的重建层厚,改变螺距时SSP的FWHM基本保持不变。②图像噪声测试结果：准直器宽度、螺距相同时,随着层厚的增大,图像噪声有明显降低;层厚、螺距相同时,准直器宽度减小,图像噪声降低（P〈0.05）。对于相同的准直器宽度,螺距改变时,图像噪声没有显著差别（P〉0.05）。结论对于多排螺旋CT,卷积重建算法、螺距和准直器宽度的变化对SSP的影响很小。螺距的变化对噪声的影响不大,而层厚和准直器宽度的选择对图像噪声影响明显。在临床实际操作中,需要综合考虑影响图像质量诸因素之间的关系,根据临床需要选择最佳方案。

Research on the parameters for impacting the ordinate/Z-axis resolution and image noise of multi-detector spiral CT

Objective To evaluate the effect of slice thickness, collimation, pitch and reconstruction algorithm on image noise and ordinate/Z-axis resolution or slice sensitivity profile (SSP). Methods Different slice thickness, collimation, pitch and reconstruction algorithm were used to scan the phantoms. The effect of different parameters on SSP and image noise were compared. Results For SSP measurements, the FWHMs were maintained well when pitch and reconstruction algorithm were changed. For image noise measurements, the image noise decreased with increasing slice thickness and reducing collimation width (P<0.05). There was no significant difference on image noise when pitch was changed (P>0.05). Conclusion For multislice spiral CT, the reconstruction algorithm, pitch and collimation have no significant effect on SSP. There is no obvious relationship between image noise and pitch, but the slice thickness and collimation have obvious effect on image noise. We should take into account these parameters which impact the image quality so as to optimize CT scanning protocol.