Eichner Cornelius, Setsompop Kawin, Koopmans Peter J, Lützkendorf Ralf, Norris David G, Turner Robert, Wald Lawrence L, Heidemann Robin M
Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, Massachusetts, USA; Harvard Medical School, Boston, Massachusetts, USA.
Magn Reson Med. 2014 Apr;71(4):1518-25. doi: 10.1002/mrm.24809. Epub 2013 Jun 24.
Diffusion magnetic resonance imaging (dMRI) data with very high isotropic resolution can be obtained at 7T. However, for extensive brain coverage, a large number of slices is required, resulting in long acquisition times (TAs). Recording multiple slices simultaneously (SMS) promises to reduce the TA.
A combination of zoomed and parallel imaging is used to achieve high isotropic resolution dMRI data with a low level of distortions at 7T. The blipped-CAIPI (controlled aliasing in parallel imaging) approach is used to acquire several slices simultaneously. Due to their high radiofrequency (RF) power deposition and ensuing specific absorption rate (SAR) constraints, the commonly used multiband (MB) RF pulses for SMS imaging are inefficient at 7T and entail long repetition times, counteracting the usefulness of SMS acquisitions. To address this issue, low SAR multislice Power Independent of Number of Slices RF pulses are employed.
In vivo dMRI results with and without SMS acceleration are presented at different isotropic spatial resolutions at ultra high field strength. The datasets are recorded at a high angular resolution to detect fiber crossings.
From the results and compared with earlier studies at these resolutions, it can be seen that scan time is significantly reduced, while image quality is preserved.
在7T磁场下可获得具有非常高各向同性分辨率的扩散磁共振成像（dMRI）数据。然而，为了实现广泛的脑覆盖，需要大量的切片，这导致采集时间（TA）较长。同时记录多个切片（SMS）有望减少采集时间。
采用缩放成像和平行成像相结合的方法，在7T磁场下获得具有低畸变水平的高各向同性分辨率dMRI数据。使用 blipped-CAIPI（并行成像中的可控混叠）方法同时采集多个切片。由于其高射频（RF）功率沉积和随之而来的比吸收率（SAR）限制，用于SMS成像的常用多频段（MB）RF脉冲在7T磁场下效率低下，且需要较长的重复时间，这抵消了SMS采集的优势。为了解决这个问题，采用了低SAR的与切片数量无关的多层RF脉冲。
展示了在超高场强下不同各向同性空间分辨率下有无SMS加速的体内dMRI结果。数据集以高角分辨率记录以检测纤维交叉。
从结果以及与这些分辨率下早期研究的比较可以看出，扫描时间显著减少，同时图像质量得以保持。
