Sabanci University, Tuzla, Istanbul 34956, Turkey.
Med Phys. 2013 Oct;40(10):101903. doi: 10.1118/1.4819938.
A key challenge for image guided coronary interventions is accurate and absolutely robust image registration bringing together preinterventional information extracted from a three-dimensional (3D) patient scan and live interventional image information. In this paper, the authors present a novel scheme for 3D to two-dimensional (2D) rigid registration of coronary arteries extracted from preoperative image scan (3D) and a single segmented intraoperative x-ray angio frame in frequency and spatial domains for real-time angiography interventions by C-arm fluoroscopy.
Most existing rigid registration approaches require a close initialization due to the abundance of local minima and high complexity of search algorithms. The authors' method eliminates this requirement by transforming the projections into translation-invariant Fourier domain for estimating the 3D pose. For 3D rotation recovery, template Digitally Reconstructed Radiographs (DRR) as candidate poses of 3D vessels of segmented computed tomography angiography are produced by rotating the camera (image intensifier) around the DICOM angle values with a specific range as in C-arm setup. The authors have compared the 3D poses of template DRRs with the segmented x-ray after equalizing the scales in three domains, namely, Fourier magnitude, Fourier phase, and Fourier polar. The best rotation pose candidate was chosen by one of the highest similarity measures returned by the methods in these domains. It has been noted in literature that frequency domain methods are robust against noise and occlusion which was also validated by the authors' results. 3D translation of the volume was then recovered by distance-map based BFGS optimization well suited to convex structure of the authors' objective function without local minima due to distance maps. A novel automatic x-ray vessel segmentation was also performed in this study.
Final results were evaluated in 2D projection space for patient data; and with ground truth values and landmark distances for the images acquired with a solid phantom vessel. Results validate that rotation recovery in frequency domain is robust against differences in segmentations in two modalities. Distance-map translation is successful in aligning coronary trees with highest possible overlap.
Numerical and qualitative results show that single view rigid alignment in projection space is successful. This work can be extended with multiple views to resolve depth ambiguity and with deformable registration to account for nonrigid motion in patient data.
图像引导的冠状动脉介入治疗的一个关键挑战是准确且绝对稳健的图像配准，将从三维（3D）患者扫描中提取的术前信息与实时介入图像信息相结合。在本文中，作者提出了一种新的方案，用于从术前图像扫描（3D）中提取的冠状动脉与术中单个分割的 X 射线血管造影帧在频率和空间域中的 3D 到 2D（2D）刚性配准，用于 C 臂透视实时血管造影介入。
大多数现有的刚性配准方法由于存在大量的局部最小值和搜索算法的高复杂性，需要进行紧密的初始化。作者的方法通过将投影转换为平移不变的傅里叶域来估计 3D 姿态，从而消除了这一要求。对于 3D 旋转恢复，通过以与 C 臂设置中相同的方式围绕 DICOM 角度值旋转相机（图像增强器）来生成作为分割 CT 血管造影 3D 血管候选姿态的模板数字重建射线照片（DRR）。作者通过在三个域中（即傅里叶幅度、傅里叶相位和傅里叶极）对模板 DRR 的 3D 姿态与分割后的 X 射线进行均衡缩放，然后比较了它们的 3D 姿态。通过这些域中的方法返回的最高相似性度量之一选择最佳旋转姿态候选。文献中指出，频率域方法对噪声和遮挡具有鲁棒性，作者的结果也验证了这一点。然后通过基于距离图的 BFGS 优化来恢复体积的 3D 平移，该优化非常适合于作者的目标函数的凸结构，而不会由于距离图而产生局部最小值。在这项研究中，还进行了一种新颖的自动 X 射线血管分割。
最终结果在患者数据的 2D 投影空间中进行了评估；并与使用固体模拟血管获得的图像的地面真实值和地标距离进行了评估。结果验证了频率域中的旋转恢复对两种模式的分割差异具有鲁棒性。距离图平移成功地将冠状动脉树对齐，实现了最大可能的重叠。
数值和定性结果表明，在投影空间中进行单视图刚性配准是成功的。这项工作可以通过增加多个视图来解决深度模糊性，并通过可变形配准来考虑患者数据中的非刚性运动来扩展。
