Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand.
Medical Imaging System Research Team, Assistive Technology and Medical Devices Research Center, National Science and Technology Development Agency, Pathum Thani, Thailand.
BMC Med Imaging. 2022 Sep 5;22(1):160. doi: 10.1186/s12880-022-00881-8.
Iterative reconstruction for cone-beam computed tomography (CBCT) has been applied to improve image quality and reduce radiation dose. In a case where an object's actual projection is larger than a flat panel detector, CBCT images contain truncated data or incomplete projections, which degrade image quality inside the field of view (FOV). In this work, we propose truncation effect reduction for fast iterative reconstruction in CBCT imaging.
The volume matrix size of the FOV and the height of projection images were extrapolated to a suitable size. These extended projections were reconstructed by fast iterative reconstruction. Moreover, a smoothing parameter for noise regularization in iterative reconstruction was modified to reduce the accumulated error while processing. The proposed work was evaluated by image quality measurements and compared with conventional filtered backprojection (FBP). To validate the proposed method, we used a head phantom for evaluation and preliminarily tested on a human dataset.
In the experimental results, the reconstructed images from the head phantom showed enhanced image quality. In addition, fast iterative reconstruction can be run continuously while maintaining a consistent mean-percentage-error value for many iterations. The contrast-to-noise ratio of the soft-tissue images was improved. Visualization of low contrast in the ventricle and soft-tissue images was much improved compared to those from FBP using the same dose index of 5 mGy.
Our proposed method showed satisfactory performance to reduce the truncation effect, especially inside the FOV with better image quality for soft-tissue imaging. The convergence of fast iterative reconstruction tends to be stable for many iterations.
锥形束计算机断层扫描（CBCT）的迭代重建技术已被应用于提高图像质量和降低辐射剂量。在物体的实际投影大于平板探测器的情况下，CBCT 图像包含截断数据或不完整的投影，这会降低视场（FOV）内的图像质量。在这项工作中，我们提出了一种用于 CBCT 成像快速迭代重建的截断效应减少方法。
将 FOV 的体积矩阵大小和投影图像的高度外推到合适的大小。这些扩展的投影通过快速迭代重建进行重建。此外，还修改了迭代重建中噪声正则化的平滑参数，以减少处理过程中的累积误差。通过图像质量测量对所提出的工作进行了评估，并与传统的滤波反投影（FBP）进行了比较。为了验证所提出的方法，我们使用头部体模进行了评估，并在人体数据集上进行了初步测试。
在实验结果中，来自头部体模的重建图像显示出了增强的图像质量。此外，快速迭代重建可以连续运行，同时保持许多迭代的一致平均百分比误差值。软组织图像的对比噪声比得到了提高。与使用相同剂量指数 5 mGy 的 FBP 相比，脑室和软组织图像中的低对比度的可视化得到了显著改善。
我们提出的方法在减少截断效应方面表现出令人满意的性能，特别是在 FOV 内，对软组织成像的图像质量更好。快速迭代重建的收敛性倾向于在许多迭代中保持稳定。
