64层螺旋CT噪声测试及其影响因素分析

Measurement and evaluation of image noise at 64 slice spiral CT

目的测试和评价64层螺旋CT图像噪声及其影响因素。方法对SOMATOM Sensation 64层螺旋CT，使用临床常用的腹部扫描模式，采用不同直径的模体，不同层厚、毫安秒（mAs）、管电压（kV）、重建算法、视野和螺距等扫描参数，分别进行螺旋扫描和断面扫描，测量其图像中心感兴趣区内的标准差并进行分析。结果160mAs时，标称层厚10、7、5、3、1和0.6mm的噪声分别是8.4、9.3、10.7、13.0、21.8、28.3；120kV时，重建算法为B30 smooth、B40 smooth、B60 sharp、B70 sharp时的噪声分别是8.4、9.5、41.4、44.5；对于标称层厚5mm时，螺距为0.5、0.75、1、1.25、1.5时噪声为10．6、11、10．7、10．5、10．9；随着模体直径的增加，螺旋扫描和断面扫描时的噪声均增大；视野为200mm×200mm、150mm×150mm、100mm×100mm时的图像噪声是7．83、8．10、10．47。结论64层螺旋CT图像噪声随mAs、层厚、kV、视野的增大而减少，随模体直径的增加和高分辨率算法而增大，但不随螺距和扫描方式的改变而改变。

Objective To measure and evaluate the CT image noise and study the influencing factors at a 64-slice spiral CT system. Methods Using SOMATOM Sensation 64-slice spiral CT and body phantoms, spiral scan and axial scan were employed with different scan parameters including slice thickness, mAs, kV, reconstruction algorithm, FOV and pitch. Then standard deviation of CT images were measured and analysed. Results At 160 mAs, the image noise are 8.4, 9.3, 10.7, 13.0, 21.8, and 28.3 at different slice thickness of 10, 7, 5, 3, 1 and 0.6 mm. At 120 kV, the noise are 8.4, 9.5, 41.4, and 44.5 at different reconstruction algorithm of B30 smooth, B40 smooth, B60 sharp, B70 sharp. For nominal thickness of 5 mm, the noise are 10.6, 11, 10.7, 10.5, and 10.9 at different pitch of 0.5, 0.75, 1, 1.25, and 1.5. The noise increase along with increase of diameter of the phantoms when spiral scan and axial scan are employed. The image noise are 7.83, 8.10, and 10.47 at different FOV of 200 mm×200 mm, 150 mm×150 mm, 100 mm×100 mm. Conclusions The image noise decreases along with increase of slice thickness, mAs, kV and FOV, and increases along with increase of diameter of the phantoms and the reconstruction algorithm of high resolution. But it is independent of pitch and hardly has difference for helical and axial scanning.