Département de Radio-Oncologie et Centre de Recherche en Cancérologie, Université Laval, Centre Hospitalier Universitaire de Québec, 11 Côte du Palais, Québec, Québec G1R 2J6, Canada.
Med Phys. 2011 Jan;38(1):47-56. doi: 10.1118/1.3519988.
In permanent seed implants, 60 to more than 100 small metal capsules are inserted in the prostate, creating artifacts in x-ray computed tomography (CT) imaging. The goal of this work is to develop an automatic method for metal artifact reduction (MAR) from small objects such as brachytherapy seeds for clinical applications.
The approach for MAR is based on the interpolation of missing projections by directly using raw helical CT data (sinogram). First, an initial image is reconstructed from the raw CT data. Then, the metal objects segmented from the reconstructed image are reprojected back into the sinogram space to produce a metal-only sinogram. The Steger method is used to determine precisely the position and edges of the seed traces in the raw CT data. By combining the use of Steger detection and reprojections, the missing projections are detected and replaced by interpolation of non-missing neighboring projections.
In both phantom experiments and patient studies, the missing projections have been detected successfully and the artifacts caused by metallic objects have been substantially reduced. The performance of the algorithm has been quantified by comparing the uniformity between the uncorrected and the corrected phantom images. The results of the artifact reduction algorithm are indistinguishable from the true background value.
An efficient algorithm for MAR in seed brachytherapy was developed. The test results obtained using raw helical CT data for both phantom and clinical cases have demonstrated that the proposed MAR method is capable of accurately detecting and correcting artifacts caused by a large number of very small metal objects (seeds) in sinogram space. This should enable a more accurate use of advanced brachytherapy dose calculations, such as Monte Carlo simulations.
在永久性种子植入物中，将 60 个或更多的小金属胶囊插入前列腺中，这会在 X 射线计算机断层扫描（CT）成像中产生伪影。这项工作的目的是开发一种从小物体（如近距离放射疗法种子）自动减少金属伪影（MAR）的方法，以应用于临床。
MAR 的方法基于直接使用原始螺旋 CT 数据（射线）来插值缺失的投影。首先，从原始 CT 数据重建初始图像。然后，从重建图像中分割出金属物体，将其重新投影到射线图空间中，生成仅包含金属的射线图。Steger 方法用于在原始 CT 数据中准确确定种子轨迹的位置和边缘。通过结合使用 Steger 检测和重新投影，可以检测到缺失的投影，并通过插值非缺失的相邻投影来替换它们。
在体模实验和患者研究中，成功地检测到了缺失的投影，并大大减少了金属物体引起的伪影。通过比较未校正和校正的体模图像之间的均匀性，对算法的性能进行了量化。减少伪影算法的结果与真实背景值无法区分。
开发了一种用于种子近距离放射疗法的 MAR 的有效算法。使用原始螺旋 CT 数据对体模和临床病例进行的测试结果表明，所提出的 MAR 方法能够准确地检测和校正射线图空间中大量非常小的金属物体（种子）引起的伪影。这应该能够更准确地使用先进的近距离放射疗法剂量计算，如蒙特卡罗模拟。
