医用CT体模对高对比度分辨力检测结果的影响

Influence of Phantom on the Verification Results of High Contrast Resolution of Medical CT Images

本文分析和探讨了日常质量评价(Quality Assessment,QA)检测中体模对医用CT图像高对比度分辨力检测结果的影响。通过剖析CTP528模块的结构细节,尝试分析其设计原理,同时使用与模块结构相适应的基于标准差(Standard Deviation,SD)的调制传递函数方法计算高分检测结果。实验数据表明,在扫描模式、层厚、重建算法以及视野等扫描条件不变的情况下,仅改变管电流或管电压对高对比度分辨力检测结果的影响并不十分明显,而基于体模的检测结果明显低于图像的极限分辨率,这种差距的形成除了CT设备自身性能的因素外,体模的结构、摆放和加工误差也会带来不同程度的影响。医用CT检测体模一直被认为是"标准化"的象征,但其依然存在诸多不足之处,只有充分的了解体模,才能更好地发挥其在QA检测中的作用。

In this paper, the influence of phantom on verification results of high contrast resolution ofmedical CT images in daily Quality Assessment （QA） tests was analyzed and discussed. And the CTP528module’s design principle was analyzed under the premise of dissecting its detailed structure. Meanwhile,an Modulation Transfer Function （MTF） estimation method based on SD was used according to CTP528to calculate the high contrast resolution verification results. The experimental data demonstrated that,under the invariable conditions of scanning mode, slice thickness, reconstruction algorithm and FOV（Field of View）, the variation of tube current or tube voltage would not bring apparent change on theverification results of high contrast resolution. Moreover, in addition to the performance of CT equipmentitself, the design structure, the place means as well as the machining error of the phantom would alsobring a certain degree of influence on the verification results of high contrast resolution. Therefore, asthe CT verification phantoms have always been considered as the symbol of “standardization”, however,they still have many shortcomings. Phantoms could play their roles in QA testing better if they were fullyunderstood.