Liang Y, Kruger R A
Department of Radiology, Indiana University School of Medicine, Indianapolis 46202.
Med Phys. 1996 Feb;23(2):205-220. doi: 10.1118/1.597705.
In this paper we deal with two types of spiral scanners; one is a single-slice spiral scanner, while the other employs dual-slice technology into spiral scanning. Physical performance parameters, including image noise, contrast resolution, spatial resolution (transversal and longitudinal), and radiation exposure are measured. Computer simulations based on two interpolation methods (180 degrees and 360 degrees linear interpolation) are also used in evaluating the slice-sensitivity profile (SSP) and noise. The results show that the noise behaves in the same way for both types of scanners. The noise change, relative to that of the standard scan with the same scanning parameters, depends solely on the interpolation algorithm. Table speed and scanner geometry (either single slice or dual slice) have no effect on the noise value. For the given table speed, as well as individual detector collimation (slice width) the dual-slice scan results in better longitudinal resolution (SSP) compared to a single-slice scan if the scan is obtained with nonoverlapping slices (pitch greater than 2). This is because the dual-slice scan obtains twice the number of nonoverlapped projections for the same length, which reduces the degradation of the slice profile by using more densely arranged projections (in the longitudinal direction) for the interpolation. In the dual-slice scanner the workable scan rate is extended up to pitch 4 compared to a pitch of 2 for the single-slice scanner. Therefore, the dual-slice spiral scanner is preferred in applications requiring an increased scan rate with comparative image quality.
在本文中，我们探讨了两种类型的螺旋扫描仪；一种是单层螺旋扫描仪，另一种则将双层技术应用于螺旋扫描。我们测量了包括图像噪声、对比度分辨率、空间分辨率（横向和纵向）以及辐射剂量在内的物理性能参数。基于两种插值方法（180度和360度线性插值）的计算机模拟也被用于评估层厚灵敏度曲线（SSP）和噪声。结果表明，两种类型的扫描仪在噪声表现上是相同的。相对于具有相同扫描参数的标准扫描，噪声变化仅取决于插值算法。床速和扫描仪几何结构（单层或双层）对噪声值没有影响。对于给定的床速以及单个探测器准直（层厚），如果扫描是在非重叠层厚（螺距大于2）下进行的，那么与单层扫描相比，双层扫描在纵向分辨率（SSP）方面表现更好。这是因为对于相同长度，双层扫描获得的非重叠投影数量是单层扫描的两倍，通过使用更密集排列的投影（在纵向方向）进行插值，减少了层厚曲线的退化。在双层扫描仪中，可行的扫描速率可扩展到螺距4，而单层扫描仪的螺距为2。因此，在需要提高扫描速率且图像质量相当的应用中，双层螺旋扫描仪更受青睐。
