Department of Radiation Oncology, Duke University, Durham, NC 27710, USA.
Med Phys. 2012 Mar;39(3):1247-52. doi: 10.1118/1.3682000.
The aim of this work is to investigate the feasibility of accelerating phase contrast magnetic resonance angiography (PC-MRA) by the fast imaging method of simplified skipped phase encoding and edge deghosting with array coil enhancement (S-SPEED-ACE).
The parallel imaging method of skipped phase encoding and edge deghosting with array coil enhancement (SPEED-ACE) is simplified for imaging sparse objects like phase contrast MRA. This approach is termed S-SPEED-ACE in which k-space is sparsely sampled with skipped phase encoding at every Nth step using multiple receiver coils simultaneously. The sampled data are then Fourier transformed into a set of ghosted images, each with N-fold aliasing ghosts. Given signal sparseness of MRA, the ghosted images are modeled with a single-layer structure, in which the most dominant ghost within the potentially overlapped ghosts at each pixel is selected to represent the signal of that pixel. The single-layer model is analogous to that used in maximum-intensity-projection (MIP) that selects only the brightest signal even when there are overlapped vessels. With an algorithm based on a least-square-error solution, a deghosted image is obtained, along with a residual map for quality control. In this way, S-SPEED-ACE partially samples k-space using multiple receiver coils in parallel, and yields a deghosted image with an acceleration factor of N. Without full central k-space sampling and differential filtering, S-SPEED-ACE achieves further scan time reduction with a more straightforward reconstruction. In this work, S-SPEED-ACE is demonstrated to accelerate a computer simulated PC-MRA and a real human 3D PC-MRA, which was acquired using a clinical 1.5 T scanner on a healthy volunteer.
Images are reconstructed by S-SPEED-ACE to achieve an undersampling factor of up to 8.3 with four receiver coils. The reconstructed images generally have comparable quality as that of the reference images reconstructed from full k-space data. Maximum-intensity-projection images generated from the reconstructed images also demonstrated to be consistent as those from the reference images.
By taking advantage of signal sparsity naturally existing in the data, SPEED-ACE was simplified and its efficiency was improved. The feasibility of the proposed S-SPEED-ACE is demonstrated in this work with simulated sampling of an actual 3D head PC-MRA scan.
本研究旨在探讨利用简化相位编码和边缘去伪影的快速成像方法（S-SPEED-ACE）加速相位对比磁共振血管造影（PC-MRA）的可行性。
本研究简化了相位编码和边缘去伪影的并行成像方法（SPEED-ACE），以用于稀疏物体成像，如相位对比 MRA。这种方法称为 S-SPEED-ACE，其中在每个第 N 步使用多个接收线圈同时进行稀疏相位编码，对 k 空间进行稀疏采样。然后对采样数据进行傅里叶变换，得到一组具有 N 倍混叠伪影的图像。由于 MRA 的信号稀疏性，对伪影图像进行建模时采用了单层结构，其中在每个像素的潜在重叠伪影中选择最主要的伪影来代表该像素的信号。这种单层模型类似于最大强度投影（MIP）中使用的模型，即使存在重叠血管，MIP 也只选择最亮的信号。通过基于最小二乘误差解的算法，获得去伪影图像以及质量控制的残差图。通过这种方式，S-SPEED-ACE 利用多个接收线圈并行对 k 空间进行部分采样，并以 N 倍的加速因子得到去伪影图像。由于没有进行全中心 k 空间采样和差分滤波，S-SPEED-ACE 实现了进一步的扫描时间缩短，同时具有更简单的重建过程。本研究利用计算机模拟的 PC-MRA 和在健康志愿者上使用临床 1.5 T 扫描仪采集的真实人体 3D PC-MRA 来验证 S-SPEED-ACE 的加速效果。
通过 S-SPEED-ACE 重建图像，利用四个接收线圈实现了高达 8.3 的欠采样因子。重建图像的质量通常与从全 k 空间数据重建的参考图像相当。从重建图像生成的最大强度投影图像也与参考图像一致。
本研究利用数据中固有的信号稀疏性，简化了 SPEED-ACE，并提高了其效率。通过模拟实际的 3D 头部 PC-MRA 扫描，本研究验证了所提出的 S-SPEED-ACE 的可行性。
