La Rivière Patrick J, Pan Xiaochuan
Department of Radiology, The University of Chicago, Illinois 60637, USA.
Med Phys. 2002 Jun;29(6):943-51. doi: 10.1118/1.1477229.
Volumes reconstructed by standard methods from single-slice helical computed tomography (CT) data have been shown to have noise levels that are highly nonuniform relative to those in conventional CT. These noise nonuniformities can affect low-contrast object detectability and have also been identified as the cause of the zebra artifacts that plague maximum intensity projection (MIP) images of such volumes. While these spatially variant noise levels have their root in the peculiarities of the helical scan geometry, there is also a strong dependence on the interpolation and reconstruction algorithms employed. In this paper, we seek to develop image reconstruction strategies that eliminate or reduce, at its source, the nonuniformity of noise levels in helical CT relative to that in conventional CT. We pursue two approaches, independently and in concert. We argue, and verify, that Fourier-based longitudinal interpolation approaches lead to more uniform noise ratios than do the standard 360LI and 180LI approaches. We also demonstrate that a Fourier-based fan-to-parallel rebinning algorithm, used as an alternative to fanbeam filtered backprojection for slice reconstruction, also leads to more uniform noise ratios, even when making use of the 180LI and 360LI interpolation approaches.
通过标准方法从单层螺旋计算机断层扫描（CT）数据重建的容积已被证明，其噪声水平相对于传统CT中的噪声水平具有高度的不均匀性。这些噪声不均匀性会影响低对比度物体的可检测性，并且也已被确定为困扰此类容积的最大强度投影（MIP）图像出现斑马伪影的原因。虽然这些空间变化的噪声水平源于螺旋扫描几何结构的特殊性，但也强烈依赖于所采用的插值和重建算法。在本文中，我们试图开发图像重建策略，从源头上消除或减少螺旋CT中相对于传统CT的噪声水平不均匀性。我们独立并协同地采用两种方法。我们论证并验证，基于傅里叶的纵向插值方法比标准的360LI和180LI方法能带来更均匀的噪声比。我们还证明，作为扇形束滤波反投影用于切片重建的替代方法，基于傅里叶的扇形到平行重排算法也能带来更均匀的噪声比，即使在使用180LI和360LI插值方法时也是如此。
