Department of Radiological Technology, National Cancer Center Japan, Tokyo, Japan.
AlgoMedica, Inc., Sunnyvale, California, USA.
Med Phys. 2021 Sep;48(9):4993-5003. doi: 10.1002/mp.15104. Epub 2021 Jul 31.
In this study, the noise reduction properties of the adaptive statistical iterative reconstruction (IR) on two different CT scanners of 64 and 256-slice were compared and their differences were assessed.
The homogeneous module of the ACR CT phantom was scanned on the 64 and 256 slices CT scanners from the same vendor in the range of 15-40 mA. On each scanner, the data were reconstructed using filtered back projection (FBP) and at all strengths of IR with the STANDARD kernel. For each reconstruction, a 3D noise power spectrum (NPS) was calculated and the central frequency ratio in the xy plane (CFR ), CFR in the z-direction (CFR ), and noise magnitude ratio (NMR) were derived. CFR is the central frequency ratio of NPS between the denoised image and the FBP image, and NMR is the ratio of the areas under the NPS curves. Ideally, both CFR and CFR should be near 1, indicating minimal texture changes in both xy and z directions, while NMR should be as close to 0 as possible, indicating more noise reduction.
When comparing strengths with equivalent impact on noise texture, IR on the 64-slice reduced the noise magnitude in the xy plane more than that on the 256-slice. In the z-direction, the IR on the 256-slice produced a central frequency shift on the 256-slice but not on the 64-slice. In addition, the noise reduction effects of the IR on the 256-slice were affected when radiation exposure was below 2.0 mGy, but there was no observable dose-dependence on the 64-slice.
Our noise property analysis revealed that iterative reconstructions on different scanner platforms from the same vendor can be distinct, with unique effects on the noise texture and magnitude in CT images. The IR on a 64-slice scanner provides slightly enhanced noise reduction and maintains a noise reduction rate independent of dose, unlike the one on a 256-slice scanner. Notably, the IR on the 64-slice scanner was a 2D noise reduction technique (NRT), while the one on the 256-slice was a 3D NRT. These observations showcase the impact of different NRTs on clinical CT images, even when comparing the same NRT on different scanners.
本研究旨在比较两种不同的 64 层和 256 层 CT 扫描仪上自适应统计迭代重建（IR）的降噪性能，并评估它们之间的差异。
使用相同供应商的 64 层和 256 层 CT 扫描仪对 ACR CT 体模的均匀模块进行扫描，管电流范围为 15-40mA。在每台扫描仪上，使用滤波反投影（FBP）和所有强度的 IR （STANDARD 内核）进行数据重建。对于每种重建，计算三维噪声功率谱（NPS），并导出 xy 平面中的中心频率比（CFR）、z 方向中的 CFR（CFR）和噪声幅度比（NMR）。CFR 是去噪图像和 FBP 图像之间 NPS 的中心频率比，NMR 是 NPS 曲线下面积的比值。理想情况下，CFR 和 CFR 都应接近 1，表明 xy 和 z 方向的纹理变化最小，而 NMR 应尽可能接近 0，表明降噪效果更好。
当比较对噪声纹理具有等效影响的强度时，64 层 IR 比 256 层 IR 更能降低 xy 平面的噪声幅度。在 z 方向，256 层的 IR 产生了一个在 256 层上的中心频率偏移，但在 64 层上没有。此外，当辐射剂量低于 2.0mGy 时，256 层 IR 的降噪效果会受到影响，但在 64 层上没有观察到剂量依赖性。
我们的噪声特性分析表明，来自同一供应商的不同扫描仪平台上的迭代重建可能存在差异，对 CT 图像中的噪声纹理和幅度有独特的影响。与 256 层扫描仪相比，64 层扫描仪上的 IR 提供了略微增强的降噪效果，并且降噪率与剂量无关。值得注意的是，64 层扫描仪上的 IR 是一种 2D 降噪技术（NRT），而 256 层扫描仪上的 IR 是一种 3D NRT。这些观察结果表明，即使在比较不同扫描仪上的相同 NRT 时，不同的 NRT 也会对临床 CT 图像产生影响。
