Physical performance evaluation of a 256-slice CT-scanner for four-dimensional imaging
Physical performance evaluation of a 256-slice CT-scanner for four-dimensional imaging
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DOI：
10.1118/1.1747758
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发表时间：
2004-06-01
期刊：
影响因子：
3.8
通讯作者：
Kusakabe, M
中科院分区：
文献类型：
--
作者：
Mori, S;Endo, M;Kusakabe, M
我们已经开发了一个原型256层CT扫描仪的四维（413）成像，采用连续旋转的锥束。由于沿沿着圆形轨道的锥束扫描不能收集完整的数据集以进行体积[三维（313）图像]的精确重建，因此可能会导致缺点或伪影。为了检查锥束数据收集对图像质量的影响，我们评估了具有0.5 mm切片的原型256层CT扫描仪的物理性能，并将其与具有0.75 mm切片的16层CT扫描仪进行了比较。结果，我们发现图像噪声、均匀性和高对比度可检测性与z坐标无关。在失真测量中观察到Feldkamp伪影。切片敏感性曲线（SSP）的半高宽（FWHM）随z坐标的增加而增加，但这似乎是由其他原因引起的，而不是数据的不完整。关于低对比度可检测性，较小的物体在中平面（z = 0 mm）处比在z = 40 mm处更清楚地检测到，尽管圆形带状伪影影响检测。16层和256层扫描仪之间的比较表明，16层扫描仪在SSP、低对比度可检测性和失真方面的性能更好。256层扫描仪在除失真测量（Feldkamp伪影）之外的其他方面的缺陷似乎部分是由扫描仪的原型性质引起的，应在未来的扫描仪中加以改进。两种CT的图像噪声、均匀性和高对比度可检测性几乎相同。在PSF方面，256层扫描仪上级16层扫描仪，尽管这是由256层扫描仪较小的横向射束宽度引起的。为了全面比较两种扫描仪的曝光剂量、噪声、层厚和横向空间分辨率，计算K = Dsigma（2）ha（3），其中D为曝光剂量（CT剂量指数），sigma为噪声大小，它是层厚（SSP的FWHM），a是横向空间分辨率（PSF的FWHM）。结果表明，16层扫描仪的K值大25%，256层扫描仪在中平面的有效性是16层扫描仪的1.25倍。256层扫描仪K值的优势可能部分是由于广角锥束扫描减少了浪费的曝光量。尽管256层扫描仪存在一些问题，但它获得了约1.0 mm的体积数据如果分辨率由PSF或SSP的FWHM定义，则对于在1 s扫描中沿着z轴的宽视场（约100 mm长），分辨率为（横向）x 1.3 rum（纵向），这对于拍摄运动器官的动态3D（4D）图像非常有用。（D 2004年美国医学物理学家协会。
We have developed a prototype 256-slice CT-scanner for four-dimensional (413) imaging that employs continuous rotations of a cone-beam. Since a cone-beam scan along a circular orbit does not collect a complete set of data to make an exact reconstruction of a volume [three-dimensional (313) image], it might cause disadvantages or artifacts. To examine effects of the cone-beam data collection on image quality, we have evaluated physical performance of the prototype 256-slice CT-scanner with 0.5 mm slices and compared it to that of a 16-slice CT-scanner with 0.75 mm slices. As a result, we found that image noise, uniformity, and high contrast detectability were independent of z coordinate. A Feldkamp artifact was observed in distortion measurements. Full width at half maximum (FWHM) of slice sensitivity profiles (SSP) increased with z coordinate though it seemed to be caused by other reasons than incompleteness of data. With regard to low contrast detectability, smaller objects were detected more clearly at the midplane (z = 0 mm) than at z = 40 mm, though circular-band like artifacts affected detection. The comparison between the 16-slice and the 256-slice scanners showed better performance for the 16-slice scanner regarding the SSP, low contrast detectability, and distortion. The inferiorities of the 256-slice scanner in other than distortion measurement (Feldkamp artifact) seemed to be partly caused by the prototype nature of the scanner and should be improved in the future scanner. The image noise, uniformity, and high contrast detectability were almost identical for both CTs. The 256-slice scanner was superior to the 16-slice scanner regarding the PSF, though it was caused by the smaller transverse beam width of the 256-slice scanner. In order to compare both scanners comprehensively in terms of exposure dose, noise, slice thickness, and transverse spatial resolution, K = Dsigma(2)ha(3) was calculated, where D was exposure dose (CT dose index), sigma was magnitude of noise, It was slice thickness (FWHM of SSP), and a was transverse spatial resolution (FWHM of PSF). The results showed that the K value was 25% larger for the 16-slice scanner, and that the 256-slice scanner was 1.25 times more effective than the 16-slice scanner at the midplane. The superiority in K value for the 256-slice scanner might be partly caused by decrease of wasted exposure with a wide-angle cone-beam scan. In spite of the several problems of the 256-slice scanner, it took a volume data approximately 1.0 mm (transverse) x 1.3 rum (longitudinal) resolution for a wide field of view (approximately 100 mm long) along the z axis in a 1 s scan if resolution was defined by the FWHM of the PSF or the SSP, which should be very useful to take dynamic 3D (4D) images of moving organs. (D 2004 American Association of Physicists in Medicine.