Chang Zheng, Xiang Qing-San
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.
Med Phys. 2007 Aug;34(8):3173-82. doi: 10.1118/1.2750966.
The fast imaging method named skipped phase encoding and edge deghosting (SPEED) has been demonstrated to reduce scan time considerably with typical magnetic resonance imaging data. In this work, SPEED is simplified with improved efficiency to accelerate the scan of sparse objects; we refer to this method as S-SPEED. S-SPEED partially samples k-space into two interleaved data sets, each with the same skip size of N but a different relative shift in phase encoding. The sampled data are then Fourier transformed into two ghosted images with N aliasing ghosts. Given the sparseness of signal distribution, the ghosted images are simply modeled with a single-layer structure, analogous to that used in maximum-intensity projection. With an algorithm based on a least-square-error solution, a deghosted image is solved, and a residual map is output for quality control. S-SPEED can be generalized to include more layers with additional acquisitions for refined results. Without differential filtering and full central k-space sampling, S-SPEED reduces scan time further and achieves more straightforward reconstruction, as compared with SPEED. In this work, S-SPEED is applied to accelerate magnetic resonance angiography (MRA) by taking advantage of the sparse nature of MRA data. With sparse phantom data and in vivo phase contrast MRA data, S-SPEED is demonstrated to achieve satisfactory results with an acceleration factor of 5.5 using a single coil.
名为跳跃相位编码和边缘去鬼影（SPEED）的快速成像方法已被证明能显著减少典型磁共振成像数据的扫描时间。在这项工作中，SPEED被简化并提高了效率，以加速对稀疏物体的扫描；我们将这种方法称为S-SPEED。S-SPEED将k空间部分采样为两个交错数据集，每个数据集具有相同的跳跃大小N，但在相位编码上有不同的相对偏移。然后对采样数据进行傅里叶变换，得到两个带有N个混叠鬼影的鬼影图像。考虑到信号分布的稀疏性，鬼影图像简单地用单层结构建模，类似于最大强度投影中使用的结构。通过基于最小二乘误差解的算法，求解出一个去鬼影图像，并输出一个残差图用于质量控制。S-SPEED可以推广到包括更多层，并通过额外采集以获得更精确的结果。与SPEED相比，S-SPEED无需差分滤波和完整的中心k空间采样，进一步减少了扫描时间并实现了更直接的重建。在这项工作中，S-SPEED利用磁共振血管造影（MRA）数据的稀疏特性来加速MRA。使用稀疏体模数据和体内相位对比MRA数据，S-SPEED被证明使用单个线圈以5.5的加速因子能取得令人满意的结果。
