Density-weighted concentric rings k-space trajectory for 1H magnetic resonance spectroscopic imaging at 7T
Density-weighted concentric rings k-space trajectory for 1H magnetic resonance spectroscopic imaging at 7T
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DOI：
10.1002/nbm.3838
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发表时间：
2018-01-01
影响因子：
2.9
通讯作者：
Emir, Uzay E.
中科院分区：
文献类型：
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作者：
Chiew, Mark;Jiang, Wenwen;Emir, Uzay E.
研究表明，采用螺旋和传统相位编码轨迹的密度加权 (DW) k 空间采样可减少磁共振波谱成像 (MRSI) 中的空间旁瓣。在这项研究中，我们为 DW-MRSI 提出了一种新的同心环轨迹 (CRT)，它以与空间各向同性汉宁窗成比例的密度对 k 空间进行采样。在模拟、模型和体内实验中，将两种不同 DW-CRT 的特性与径向等距 (RE) CRT 和回波平面光谱成像 (EPSI) 轨迹进行了比较。这些实验在 7 T 下进行，具有固定的标称体素尺寸和匹配的采集时间，结果表明两种 DW-CRT 设计通过抑制旁瓣改善了空间响应函数的形状，同时也提高了信噪比 (SNR)。在 8 分钟 3 秒内获得运动皮层特定感兴趣区域的所有轨迹的高质量光谱，面内分辨率为 7.5 x 7.5 mm(2)。由于硬件限制，仅针对 RE 和 DW-CRT 轨迹之一获取面内分辨率为 5 x 5 mm(2) 且采集时间为 12 分钟 48 秒的高空间分辨率光谱，而不是针对 EPSI。对于所有体模和体内实验，DW-CRT 产生了最高的 SNR。 DW-CRT 方法实现的体内光谱质量允许使用 LCModel 分析对包括 N-乙酰天冬氨酰谷氨酸、β-氨基丁酸和谷胱甘肽在内的八种代谢物进行可靠的代谢图谱，且 Cramer-Rao 下限低于 50%。最后，使用 DW-CRT 在健康受试者中以 5 x 5 mm(2) 的高平面内分辨率实现了全脑切片的高质量代谢图谱。这些发现表明，我们的 DW-CRT MRSI 技术可以在 MRI 系统上并在临床可行的采集时间内稳定运行。
It has been shown that density-weighted (DW) k-space sampling with spiral and conventional phase encoding trajectories reduces spatial side lobes in magnetic resonance spectroscopic imaging (MRSI). In this study, we propose a new concentric ring trajectory (CRT) for DW-MRSI that samples k-space with a density that is proportional to a spatial, isotropic Hanning window. The properties of two different DW-CRTs were compared against a radially equidistant (RE) CRT and an echo-planar spectroscopic imaging (EPSI) trajectory in simulations, phantoms and in vivo experiments. These experiments, conducted at 7 T with a fixed nominal voxel size and matched acquisition times, revealed that the two DW-CRT designs improved the shape of the spatial response function by suppressing side lobes, also resulting in improved signal-to-noise ratio (SNR). High-quality spectra were acquired for all trajectories from a specific region of interest in the motor cortex with an in-plane resolution of 7.5 x 7.5 mm(2) in 8 min 3 s. Due to hardware limitations, high-spatial-resolution spectra with an in-plane resolution of 5 x 5 mm(2) and an acquisition time of 12 min 48 s were acquired only for the RE and one of the DW-CRT trajectories and not for EPSI. For all phantom and in vivo experiments, DW-CRTs resulted in the highest SNR. The achieved in vivo spectral quality of the DW-CRT method allowed for reliable metabolic mapping of eight metabolites including N-acetylaspartylglutamate, -aminobutyric acid and glutathione with Cramer-Rao lower bounds below 50%, using an LCModel analysis. Finally, high-quality metabolic mapping of a whole brain slice using DW-CRT was achieved with a high in-plane resolution of 5 x 5 mm(2) in a healthy subject. These findings demonstrate that our DW-CRT MRSI technique can perform robustly on MRI systems and within a clinically feasible acquisition time.