16层螺旋CT的z轴空间分辨力测试

Measurement of z-direction spatial resolution for a 16-slice spiral CT system

目的:采用主客观两种方法评价16层螺旋CT系统的z轴空间分辨力,分析16层螺旋CT的螺距(Pitch)对z轴空间分辨力的影响。方法:把Catphan500模体的CTP528模块水平放置在检查床面上,使用Somatom Cardiac16层CT机和腹部螺旋扫描模式:准直宽度0.75mm×16,重建间隔0.1mm,重建层厚0.75mm,不同螺距进行扫描,然后重建图像。在后处理工作站对各Pitch的序列图像进行冠状位多平面重组后目测图像上z轴方向可识别的线对测试卡的最大线对数。使用上述扫描条件,对Delta模体进行扫描,制作不同螺距的MTF曲线。结果:采用线对测试卡测试的Pitch分别为0.75、1.00、1.25的z轴空间分辨力是10、9、9LP/cm。采用MTF方法测试的相对信号强度2%的空间分辨力分别是11.31、9.51、9.70LP/cm。结论:Somatom Cardiac16层螺旋CT机具有比较高的z轴空间分辨力。对于该机型,Pitch的变化对z轴空间分辨力的影响非常小。

Objective：To measure z-direction spatial resolution and analyze the relativity between scanning parameter of pitch and z-direction spatial resolution for a 16-slice spiral CT system.Methods：Using the same CT teclmique and body protocol as those used for clinical CT, CTP28 of catphan 500 phantom, in which there was a square wave test chart, was turned 90° and scanned with SOMATOM Cardiae 16-slice spiral CT system. The z-direction spatial resolution were measured in coronal multi-planar reformation （MPR） images of CTP528 with reconstruction slice width of 0. 75 mm at different pitch = 0.75, 1.00, 1.25 respectively. Then, Delta phantom was scanned with the same CT system and parameters as above and MTF curves of different pitch were got. Results：The measured z-direction spatial resolution was 10, 9, 9 LP/cm with square wave test chart at different pitch = 0.75, 1.00, 1.25 respectively. While, the resolution was 11.31, 9.51, 9.70 LP/cm at 2% MTF with MTF cttrve. Conclusion：The CT systen has high z-direction spatial resolution and z-direction spatial resolution wtfich is almost independent on pitch for SOMATOM Cardiac 16-slice spiral CT system.