Raj Ashish, Zhang Honglei, Prince Martin R, Wang Yi, Zabih Ramin
Department of Radiology, Weill Medical College of Cornell University, New York, New York 10022, USA.
Magn Reson Med. 2006 Mar;55(3):649-58. doi: 10.1002/mrm.20806.
Time-resolved contrast enhanced magnetic resonance angiography (MRA) may suffer from involuntary patient motion. It is noted that while MR signal change associated with motion is large in magnitude and has smooth phase variation in k-phase, signal change associated with vascular enhancement is small in magnitude and has rapid phase variation in k-space. Based upon this observation, a novel projection onto convex sets (POCS) algorithm is developed as an automatic iterative method to remove motion artifacts. The presented POCS algorithm consists of high-pass phase filtering and convex projections in both k-space and image space. Without input of detailed motion knowledge, motion effects are filtered out, while vasculature information is preserved. The proposed method can be effective for a large class of nonrigid motions, including through-plane motion. The algorithm is stable and converges quickly, usually within five iterations. A double-blind evaluation on a set of clinical MRA cases shows that a completely unsupervised version of the algorithm produces significantly better rank scores (P=0.038) when compared to angiograms produced manually by an experienced radiologist.
时间分辨对比增强磁共振血管造影（MRA）可能会受到患者非自主运动的影响。值得注意的是，虽然与运动相关的磁共振信号变化幅度较大，且在k空间相位变化平滑，但与血管增强相关的信号变化幅度较小，且在k空间相位变化迅速。基于这一观察结果，开发了一种新颖的凸集投影（POCS）算法，作为一种自动迭代方法来去除运动伪影。所提出的POCS算法包括在k空间和图像空间中的高通相位滤波和凸投影。无需输入详细的运动信息，即可滤除运动影响，同时保留血管系统信息。该方法对于包括层面内运动在内的一大类非刚性运动都有效。该算法稳定且收敛迅速，通常在五次迭代内即可完成。对一组临床MRA病例进行的双盲评估表明，与经验丰富的放射科医生手动生成的血管造影相比，该算法的完全无监督版本产生的排序分数显著更高（P = 0.038）。
