Chang Zheng, Xiang Qing-San
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada.
Med Phys. 2006 Oct;33(10):3758-66. doi: 10.1118/1.2349700.
The fast MRI method of skipped phase encoding and edge deghosting (SPEED) is further developed with array coil enhancement, and thus is termed SPEED-ACE. In SPEED-ACE, k space is sparsely sampled with skipped phase encoding at every Nth step using a set of receiver coils simultaneously, similar to SENSE, leading to sensitivity-weighted images with up to N layers of overlapping aliasing ghosts. The ghosted images are edge enhanced by a differential filter to yield ghosted edge maps, in which the ghost overlapping layers are greatly reduced since the sparseness of edges reduces the chance of ghost overlapping. Typical ghosted edge maps can be adequately modeled with a double-layer structure. By using data from at least three coils through least-square-error minimization, a deghosted edge map is obtained and inverse-filtered into a final deghosted image. In this way, SPEED-ACE partially samples k space with a skip size of N by using multiple receiver coils in parallel, and obtains a fairly good deghosted image with an undersampling factor of N. SPEED-ACE is not limited to the double-layer ghost model, but can be generalized to include more layers of ghosts for more flexible and improved performance. As a new parallel imaging method, SPEED-ACE was tested using in vivo data to demonstrate the possibility of achieving undersampling factors even greater than the number of receiver coils, which is so far not achievable by other parallel imaging methods.
快速磁共振成像的跳相位编码与边缘去鬼影方法（SPEED）通过阵列线圈增强得到进一步发展，因此被称为SPEED - ACE。在SPEED - ACE中，k空间在每隔第N步时使用一组接收线圈同时进行跳相位编码的稀疏采样，这与敏感性编码（SENSE）类似，会产生具有多达N层重叠混叠鬼影的敏感性加权图像。通过微分滤波器对有鬼影的图像进行边缘增强，得到有鬼影的边缘图，由于边缘的稀疏性降低了鬼影重叠的几率，其中的鬼影重叠层数大幅减少。典型的有鬼影边缘图可以用双层结构进行充分建模。通过使用来自至少三个线圈的数据，经最小二乘误差最小化处理，得到一个去鬼影的边缘图，并通过逆滤波得到最终的去鬼影图像。通过这种方式，SPEED - ACE利用多个接收线圈并行地以N为跳步大小对k空间进行部分采样，并以N为欠采样因子获得相当好的去鬼影图像。SPEED - ACE不限于双层鬼影模型，还可以推广到包含更多层鬼影的情况，以实现更灵活且性能更优。作为一种新的并行成像方法，SPEED - ACE使用体内数据进行测试，以证明实现甚至大于接收线圈数量的欠采样因子的可能性，这是目前其他并行成像方法所无法实现的。
