Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.
Magn Reson Med. 2011 Jun;65(6):1630-7. doi: 10.1002/mrm.22752. Epub 2011 Feb 1.
Multislice parallel imaging involves the simultaneous sampling of multiple parallel slices which are subsequently separated using parallel imaging reconstruction. The CAIPIRINHA technique improves this reconstruction by manipulating the phase of the RF excitation pulses to shift the aliasing pattern such that there is less aliasing energy to be reconstructed. In this work, it is shown that combining the phase manipulation used in CAIPIRINHA with a non-Cartesian (radial) sampling scheme further decreases the aliasing energy for the parallel imaging algorithm to reconstruct, thereby further increasing the degree to which a multi-channel receiver array can be utilized for parallel imaging acceleration. In radial CAIPIRINHA, individual bands (slices) in a multislice excitation are modulated with view-dependent phase, causing a destructive interference of entire slices. This destructive interference leads to a reduction in aliasing compared to the coherent shifts one observes when using this same technique with a Cartesian trajectory. Recovery of each individual slice is possible because the applied phase pattern is known, and a conjugate-gradient reconstruction algorithm minimizes the contributions from other slices. Results are presented with a standard 12-channel head coil with acceleration factors up to 14, where radial CAIPIRINHA produces an improved reconstruction when compared with Cartesian CAIPIRINHA.
多层面并行成像涉及同时采集多个平行层面，然后使用并行成像重建来分离这些层面。CAIPIRINHA 技术通过操纵 RF 激励脉冲的相位来改善这种重建，从而改变混叠模式，使需要重建的混叠能量更少。在这项工作中，已经证明，将 CAIPIRINHA 中使用的相位操作与非笛卡尔（径向）采样方案相结合，可以进一步减少并行成像算法要重建的混叠能量，从而进一步增加多通道接收器阵列可用于并行成像加速的程度。在径向 CAIPIRINHA 中，多层面激发中的各个带（层面）通过与视图相关的相位进行调制，导致整个层面的相消干涉。与使用笛卡尔轨迹的相同技术观察到的相干移位相比，这种相消干涉导致混叠减少。由于已知施加的相位模式，因此可以恢复每个单独的切片，并且共轭梯度重建算法可以最小化来自其他切片的贡献。在具有高达 14 倍加速因子的标准 12 通道头部线圈上呈现了结果，其中与笛卡尔 CAIPIRINHA 相比，径向 CAIPIRINHA 产生了改进的重建。
