锥束CT成像质量影响因素研究

Study on the Factors Influencing the Quality of Cone-beam Computed Tomography

CT成像质量受诸多因素影响,有必要系统地研究各因素带来的影响以得到更好的成像效果。基于兰州大学核科学与技术学院研制的锥束CT系统,在近探测器几何条件下,采用一铝制标准件,通过对比实验研究了投影采集范围及步长、管电压及管电流、焦点尺寸、样品在转台位置、硬化校正和图像优化等因素对CT系统成像质量的影响。结果表明,当投影采集完备时,投影采集范围对成像质量影响较小,减小扫描步长能提高成像质量;适当提高管电压能降低硬化伪影,提高管电流能减小图像噪声;较小的焦点尺寸能提高图像空间分辨率,但在近探测器几何条件下不明显;样品在转台位置不影响CT系统还原样品结构;硬化校正能明显消除硬化伪影;最后,对于单一材质样品通过阈值去噪能优化图像质量。以上研究为CT系统的研制和应用提供了参考。

The imaging quality of the CT system is influenced by many factors. It is necessary to study the influence caused by each factor in order to get a better imaging result. Based on a cone-beam CT system developed by our group, and under the near detector condition, using a standard workpiece of aluminum to study the influences on the imaging quality of CT system, produced by the factors of projection acquisition range and step, tube voltage and current, focal spot size, object position on turntable, beam-hardening correction and image optimizing. The results show that the influence of projection acquisition range on imaging quality is very small, and the smaller acquisition step can improve imaging quality;appropriately increasing the tube voltage can reduce the beam-hardening artifacts and enlarging the tube current can reduce image noise;the smaller focal spot size can enhance the spatial resolution of the image, but was not obvious under the near detector geometry;sample position on turntable does not affect the reconstruction result;hardening correction can greatly eliminate beam-hardening artifacts. Finally, image optimizing can improve image quality effectively. This work provides a reference for the development and application of the CT system.