用坐标下降法实现磁共振成像中三维刚性运动的高效估计
Rigid Motion Estimation using Accelerated Iterative Coordinate Descent (REACT) for MR Imaging
- 将高维优化分解为多个分段更新，每段只调一个时间片的运动参数
- 在真实呼吸数据上，冠状动脉锐度提升超过传统方法和非刚性校正法
- 适合需要快速精准运动补偿的动态MRI研究者使用
目的：开发一种计算可行的 autofocus 方法，用于磁共振成像中的三维刚性运动估计。方法：提出的方法 REACT 假设运动轨迹为分段常数，通过优化图像质量指标来估计各时间片段的刚性运动参数。采用坐标下降法将高维优化问题分解为一系列子问题，每个子问题仅更新单个时间片段的运动参数。在合适采集条件下，假设每个子问题的目标函数近似局部凸，进而使用无导数求解器求解，避免了全网格搜索。数值模拟验证了局部凸性假设。在真实自由呼吸冠状动脉磁共振血管成像数据集（3D cones 轨迹，基于图像导航器 iNAVs）上评估 REACT，与 autofocus 非刚性运动校正方法对比。使用无界图像边缘轮廓锐度（u-IEPA）量化冠状动脉清晰度。结果：数值模拟显示，当当前运动估计接近真值时，子问题目标面近似局部凸。在体内实验中，REACT 在左前降支（LAD）和右冠状动脉上的 u-IEPA 均高于传统 iNAV 翻译运动估计方法，且在 LAD 上优于非刚性校正方法。结论：本研究证实坐标下降法在 MR 成像 autofocus 运动校正中的可行性。
原文摘要 · Abstract (English)
Purpose: To develop a computationally viable autofocus method for estimating 3D rigid motion in MR imaging. Theory and Methods: The proposed method, REACT, assumes a piecewise-constant motion trajectory and estimates the rigid motion parameters of individual temporal segments by optimizing an image-quality metric. Coordinate descent is adopted to decompose the high-dimensional optimization problem into a series of subproblems, each updating the motion parameters of a single temporal segment. The cost function of each subproblem is assumed to be approximately locally convex under suitable acquisition conditions. Each subproblem is then solved using a derivative-free solver, thereby avoiding an exhaustive grid search. Numerical simulations were conducted to investigate the local convexity assumption. REACT was evaluated for respiratory motion correction on in vivo free-breathing coronary MR angiography datasets acquired using a 3D cones trajectory with image-based navigators (iNAVs). An autofocus nonrigid motion correction method was also evaluated for comparison. Coronary artery sharpness was quantified using unbounded image edge profile acutance (u-IEPA). Results: In numerical simulations, the objective surfaces of the subproblems were approximately locally convex when the current motion estimate was close to the desired solution. In the in vivo study, REACT yielded higher u-IEPA than the conventional iNAV-based translational motion-estimation method for both the left anterior descending artery (LAD) and right coronary artery. REACT also yielded higher u-IEPA for the LAD than the autofocus nonrigid motion correction method. Conclusion: This study demonstrates the feasibility of coordinate descent for autofocus motion correction in MR imaging.
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