Institute of Medical Engineering, Graz University of Technology, Graz, Austria.
BioTechMed-Graz, Graz, Austria.
Magn Reson Med. 2019 Feb;81(2):881-892. doi: 10.1002/mrm.27434. Epub 2018 Oct 12.
Highly accelerated B -mapping based on the Bloch-Siegert shift to allow 3D acquisitions even within a brief period of a single breath-hold.
The B dependent Bloch-Siegert phase shift is measured within a highly subsampled 3D-volume and reconstructed using a two-step variational approach, exploiting the different spatial distribution of morphology and B -field. By appropriate variable substitution the basic non-convex optimization problem is transformed in a sequential solution of two convex optimization problems with a total generalized variation (TGV) regularization for the morphology part and a smoothness constraint for the B -field. The method is evaluated on 3D in vivo data with retro- and prospective subsampling. The reconstructed B -maps are compared to a zero-padded low resolution reconstruction and a fully sampled reference.
The reconstructed B -field maps are in high accordance to the reference for all measurements with a mean error below 1% and a maximum of about 4% for acceleration factors up to 100. The minimal error for different sampling patterns was achieved by sampling a dense region in k-space center with acquisition times of around 10-12 s for 3D-acquistions.
The proposed variational approach enables highly accelerated 3D acquisitions of Bloch-Siegert data and thus full liver coverage in a single breath hold.
基于 Bloch-Siegert 频移的高度加速 B 映射，允许在单次屏气的短暂时间内进行 3D 采集。
在高度欠采样的 3D 体数据内测量 B 依赖性 Bloch-Siegert 相位移动，并使用两步变分方法进行重建，利用形态和 B 场的不同空间分布。通过适当的变量替换，将基本非凸优化问题转化为两个凸优化问题的顺序解，形态部分采用全变分（TGV）正则化，B 场采用平滑约束。该方法在具有后向和前瞻性欠采样的 3D 体内数据上进行了评估。将重建的 B 映射与零填充低分辨率重建和完全采样参考进行比较。
对于所有测量，重建的 B 场图与参考图高度一致，平均误差低于 1%，最大误差约为 4%，加速因子高达 100。对于不同的采样模式，通过在 k 空间中心密集区域进行采样，并使用约 10-12 秒的采集时间进行 3D 采集，可以实现最小误差。
所提出的变分方法能够实现 Bloch-Siegert 数据的高度加速 3D 采集，从而在单次屏气中实现完整的肝脏覆盖。
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