用于定量磁化率成像的凸集上的迭代投影法
Iterative projection onto convex sets for quantitative susceptibility mapping.
作者信息
Deng Weiran, Boada Fernando, Poser Benedikt A, Schirda Claudiu, Stenger Victor Andrew
机构信息
University of Hawaii, John A. Burns School of Medicine, Honolulu, Hawaii, USA.
出版信息
Magn Reson Med. 2015 Feb;73(2):697-703. doi: 10.1002/mrm.25155. Epub 2014 Mar 6.
PURPOSE
Quantitative susceptibility map (QSM) reconstruction is ill posed due to the zero values on the "magic angle cone" that make the maps prone to streaking artifacts. We propose projection onto convex sets (POCS) in the method of steepest descent (SD) for QSM reconstruction.
METHODS
Two convex projections, an object-support projection in the image domain and a projection in k-space were used. QSM reconstruction using the proposed SD-POCS method was compared with SD and POCS alone as well as with truncated k-space division (TKD) for numerically simulated and 7 Tesla (T) human brain phase data.
RESULTS
The QSM reconstruction error from noise-free simulated phase data using SD-POCS is at least two orders of magnitude lower than using SD, POCS, or TKD and has reduced streaking artifacts. Using the l1 -TV reconstructed susceptibility as a gold standard for 7T in vivo imaging, SD-POCS showed better image quality comparing to SD, POCS, or TKD from visual inspection.
CONCLUSION
POCS is an alternative method for regularization that can be used in an iterative minimization method such as SD for QSM reconstruction.
目的
定量磁化率图谱（QSM）重建是不适定的，因为“魔角锥”上的零值会使图谱容易出现条纹伪影。我们提出在QSM重建的最速下降法（SD）中采用凸集投影（POCS）。
方法
使用了两种凸投影，一种是图像域中的目标支撑投影，另一种是k空间中的投影。将使用所提出的SD - POCS方法进行的QSM重建与单独的SD和POCS以及截断k空间划分（TKD）进行比较，用于数值模拟和7特斯拉（T）人脑相位数据。
结果
使用SD - POCS从无噪声模拟相位数据进行的QSM重建误差比使用SD、POCS或TKD至少低两个数量级，并且条纹伪影减少。将l1 - TV重建的磁化率作为7T体内成像的金标准，通过目视检查，与SD、POCS或TKD相比，SD - POCS显示出更好的图像质量。
结论
POCS是一种正则化的替代方法，可用于诸如SD的迭代最小化方法进行QSM重建。
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