Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
J Magn Reson Imaging. 2012 Apr;35(4):976-83. doi: 10.1002/jmri.23521. Epub 2011 Dec 16.
To improve the efficiency and flexibility of acquisitions of multiple voxels in MR spectroscopy by combining two-dimensional-selective radiofrequency (2DRF) excitations and Hadamard encoding.
With 2DRF excitations (PROPELLER trajectory, 16 half-Fourier segments, each with five lines) two voxels are defined. By combining the individual 2DRF pulses with Hadamard-like encoded phases, the voxels are acquired simultaneously but the individual contributions can be isolated from the obtained spectra. This is demonstrated on a 3 Tesla whole-body MR system in phantoms and in the human brain in vivo.
Compared with sequential single-voxel acquisitions the signal efficiency increases with the number of voxels covered. Furthermore, in comparison to conventional single-voxel MRS based on cross-sectional RF excitations, 2DRF excitations offer a higher flexibility because they allow for arbitrary voxel sizes, orientations, in-plane positions, and shapes.
The presented approach improves the flexibility and efficiency of acquisitions of multiple voxels, i.e., can shorten acquisition times accordingly, and can help to reduce partial volume effects.
通过结合二维选择性射频（2DRF）激发和 Hadamard 编码，提高磁共振波谱中多个体素采集的效率和灵活性。
使用 2DRF 激发（螺旋桨轨迹，16 个半傅里叶段，每个段有 5 条线），可以定义两个体素。通过将各个 2DRF 脉冲与类似 Hadamard 的编码相位相结合，可以同时采集体素，但可以从获得的光谱中分离出各个体素的贡献。在一台 3T 全身磁共振系统上的体模和人体大脑中进行了演示。
与顺序单个体素采集相比，信号效率随覆盖的体素数量增加而增加。此外，与基于横断射频激发的常规单个体素 MRS 相比，2DRF 激发具有更高的灵活性，因为它们允许任意体素大小、方向、平面位置和形状。
所提出的方法提高了多个体素采集的灵活性和效率，即可以相应地缩短采集时间，并有助于减少部分容积效应。
