16层螺旋CT螺距对图像质量的影响

目的：研究16层螺旋CT的图像质量与螺距的关系。方法：在16层螺旋CT机上,选用轴扫、不同螺距扫描QA模型,测量分析相应图像的噪声、层厚响应曲线、高对比度空间分辨率及低对比度分辨率;观察MPR图像质量。结果：轴扫图像噪声为4.39±0.29,螺距为0.562、0.938、1.375及1.75时,分别为3.24±0.25、4.39±0.23、5.27±0.25及5.40±0.33。层厚响应曲线在轴扫中呈梯形,半高宽约为5mm;在螺旋扫描中呈铃形,半高宽也近似为5mm。高对比度空间分辨率都是0.8mm线径;低对比度分辨率都能看清1mm的小孔。螺距为0.562的MPR图像未见明显变形,螺距为0.938、1.375、1.75时有较明显的变形。结论：16层螺旋CT在螺距为0.938时扫描图像噪声与轴扫图像噪声近似;随着螺距的增大,图像噪声增大,层厚响应曲线半高宽相差不大,高对比度空间分辨率和低对比度分辨率不变,MPR重构图像质量变差。

Effects of 16-slice Spiral CT Pitch on Image Quality

Objective：To study the relations of image quality and 16-slice spiral CT pitch. Methods：By 16-slice spiral CT,the QA phantom was scanned with axial scan and different spiral pitches. Then the noise,slice sensitivity profile,high- contrast resolution and low contrast resolution of the images were measured and analysed. The image quality of multiplanar reformations （MPR） was evaluated. Results： Image noise of axial scan was （4.39 ± 0.29）, when spiral pitches were 0.562, 0. 938 ,1. 375 and 1.75, image noises were （3.24 ±0.25 ）, （ 4.39 ± 0.23 ）, （ 5.27± 0.25） and （ 5.40 ±0.33）. Slice sensitivity profile of axial scan was ladder shaped, full width at half-maximum was about 5mm. Slice sensitivity profile of spiral scan was bell shaped,full-width at half-maximum was about 5mm too. All high-contrast resolutions were 0. 8mm diameter of line. All low-contrast resolutions were able to observe a lmm hole. When spiral pitch was 0. 562, image by MPR was seen to be undistorted. When spiral pitches were 0. 938,1. 375 and 1.75, images by MPR were seen to be distorted. Conclusion： When 16-slice spiral CT spiral pitch is 0. 938,the image noise is approximately equal to that of axial scan;When spiral pitches become larger, the image noises are bigger,full-widtb -at-half-maximum of slice sensitivity profile has only slight difference,high contrast resolution and low-contrast resolution are invariable,images by MPR are of poorer quality.