Stanford University, Department of Radiology, Stanford, CA, United States.
Stanford University, Department of Radiology, Stanford, CA, United States.
Neuroimage. 2017 Jun;153:97-108. doi: 10.1016/j.neuroimage.2017.03.052. Epub 2017 Mar 28.
Geometric distortions along the phase encode direction caused by off-resonant spins are still a major issue in EPI based functional and diffusion imaging. If the off-resonance map is known it is possible to correct for distortions. Most correction methods operate as a post-processing step on the reconstructed magnitude images.
Here, we present an algebraic reconstruction method (hybrid-space SENSE) that incorporates a physics based model of off-resonances, phase inconsistencies between k-space segments, and T2*-decay during the acquisition. The method can be used to perform a joint reconstruction of interleaved acquisitions with normal (blip-up) and inverted (blip-down) phase encode direction which results in reduced g-factor penalty.
A joint blip-up/down simultaneous multi slice (SMS) reconstruction for SMS-factor 4 in combination with twofold in-plane acceleration leads to a factor of two decrease in maximum g-factor penalty while providing off-resonance and eddy-current corrected images.
We provide an algebraic framework for reconstructing diffusion weighted EPI data that in addition to the general applicability of hybrid-space SENSE to 2D-EPI, SMS-EPI and 3D-EPI with arbitrary k-space coverage along z, allows for a modeling of arbitrary spatio-temporal effects during the acquisition period like off-resonances, phase inconsistencies and T2*-decay. The most immediate benefit is a reduction in g-factor penalty if an interleaved blip-up/down acquisition strategy is chosen which facilitates eddy current estimation and ensures no loss in k-space encoding in regions with strong off-resonance gradients.
在基于 EPI 的功能和扩散成像中，由于离共振自旋引起的相位编码方向上的几何变形仍然是一个主要问题。如果知道离共振图，则可以进行失真校正。大多数校正方法在重建的幅度图像上作为后处理步骤运行。
这里，我们提出了一种代数重建方法（混合空间 SENSE），它结合了离共振、k 空间段之间的相位不一致和采集过程中的 T2*-衰减的物理模型。该方法可用于对具有正常（向上激励）和反转（向下激励）相位编码方向的交错采集进行联合重建，从而减少 g 因子的惩罚。
在结合两倍的平面内加速的情况下，用于 SMS 因子 4 的联合向上/向下同时多切片（SMS）重建导致最大 g 因子惩罚降低了两倍，同时提供了离共振和涡流校正的图像。
我们提供了一种用于重建扩散加权 EPI 数据的代数框架，除了混合空间 SENSE 对 2D-EPI、SMS-EPI 和 3D-EPI 的普遍适用性外，还允许对采集期间的任意时空效应进行建模，如离共振、相位不一致和 T2*-衰减。如果选择交错的向上/向下激励采集策略，则最直接的好处是减少 g 因子的惩罚，这有利于涡流估计，并确保在具有强离共振梯度的区域中不会丢失 k 空间编码。
