Imaging Research Laboratories, Robarts Research Institute, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada.
Imaging Research Laboratories, Robarts Research Institute, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada; Department of Medical Biophysics, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada.
Neuroimage. 2018 May 15;172:703-717. doi: 10.1016/j.neuroimage.2018.02.012. Epub 2018 Feb 13.
Multi-echo gradient echo (mGRE) sequences have been widely adapted in clinical and scientific practice for different purposes to their capability of performing Dixon MRI, generating multi-contrast images and extracting multi-parametric maps. This work aims to extend mGRE-based techniques for imaging whole head, where further technical developments are required due to the co-existence of fat and large B0 inhomogeneity in regions such as the skull base and neck. Specifically, bipolar mGRE data were acquired with a single sequence that contains both a short echo-spacing (ΔTE) echo train to capture water-fat and B0 phase shifts (for proton density fat-fraction (FF) and B0 mapping) and a longer ΔTE echo train (and long echo times) to capture subtle susceptibility variations and R2* information. The mGRE images covering the whole head (spatial resolution 1.0 × 1.0 × 2.0 mm) were acquired in 5 min. An automated processing pipeline was implemented to use the FF and B0 maps determined from the short-TE train to compensate for the effects of fat, remove the background phase for whole-head quantitative susceptibility mapping, and reduce the difficulty of spatial phase unwrapping of the long echo-time data. Data from healthy volunteers imaged on a 3 T scanner along with phantom validation are presented. Co-registered quantitative multi-parametric maps (FF, B0 inhomogeneity, R2*, local frequency shift and quantitative susceptibility) and multi-contrast images covering the whole head were successfully generated in processing times of several minutes.
多回波梯度回波 (mGRE) 序列因其能够执行 Dixon MRI、生成多对比度图像和提取多参数图的功能，已在临床和科学实践中得到广泛应用。本工作旨在扩展基于 mGRE 的技术，用于对整个头部进行成像，由于颅底和颈部等区域存在脂肪和大 B0 不均匀性，因此需要进一步的技术发展。具体来说，使用单个序列采集双极 mGRE 数据，该序列包含短回波间距 (ΔTE) 回波链，用于捕获水-脂和 B0 相移（用于质子密度脂肪分数 (FF) 和 B0 映射）和较长的 ΔTE 回波链（和长回波时间），以捕获细微的磁化率变化和 R2信息。覆盖整个头部的 mGRE 图像（空间分辨率 1.0×1.0×2.0mm）在 5 分钟内采集完成。实施了自动化处理管道，使用短 TE 列车确定的 FF 和 B0 图来补偿脂肪的影响，去除全头部定量磁化率映射的背景相位，并降低长回波时间数据的空间相位解缠的难度。呈现了在 3T 扫描仪上对健康志愿者进行成像以及体模验证的数据。成功生成了经过配准的定量多参数图（FF、B0 不均匀性、R2、局部频率偏移和定量磁化率）和覆盖整个头部的多对比度图像，处理时间仅需几分钟。
