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目的 通过实验,分析影响CT图像噪声的因素及其原因。方法 应用GEHispeedCTi及其附带QA体模1套。采用不同直径模体,不同的mA值、kV值、层厚、螺距、扫描时间、重建算法、重建矩阵和重建视野等扫描参数,分别进行螺旋和轴面扫描,测量其标准偏差并分析。结果 CT图像噪声随着mA值、kV值、层厚、扫描时间、重建视野的增大而减小,随着体模直径、重建矩阵的增大而增大;图像噪声与mAs的平方根、层厚的平方根均成反比;高分辨重建算法引起较大噪声;多数情况下,螺旋扫描图像噪声略大于相应轴面扫描图像。其他条件相同时,螺距越大,噪声越大。结论影响CT图像噪声的因素很多,正确全面地理解,对于做好CT的QA、QC工作,对于正确评价、比较CT性能十分重要。
Objective To analyze the factors influencing CT image noise and its causes through experiments. Methods One set of GEHispeedCTi and its attached QA phantom was used. The scanning parameters such as different diameter phantom, different mA value, kV value, layer thickness, pitch, scan time, reconstruction algorithm, reconstruction matrix and reconstructed field of view were used to conduct spiral and axial scanning respectively, and their standard deviations were measured and analyzed. Results The noise of CT image decreased with the increase of mA value, kV value, layer thickness, scan time and reconstruction visual field, and increased with the increase of phantom diameter and reconstruction matrix. The square root of image noise and mAs, Thick square root are inversely proportional to; high-resolution reconstruction algorithm causes greater noise; in most cases, the helical scan image noise slightly larger than the corresponding axial scan image. Other conditions are the same, the greater the pitch, the greater the noise. Conclusion There are many factors affecting the CT image noise. Correct and comprehensive understanding of CT QA and QC work is very important for correct evaluation and comparison of CT performance.