Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02129, USA.
NMR Biomed. 2012 Feb;25(2):195-209. doi: 10.1002/nbm.1730. Epub 2011 Jul 20.
In this work we introduce the concept of correlation chemical shift imaging (CCSI). Novel CCSI pulse sequences are demonstrated on clinical scanners for two-dimensional Correlation Spectroscopy (COSY) and Total Correlation Spectroscopy (TOCSY) imaging experiments. To date there has been limited progress reported towards a feasible and robust multivoxel 2D COSY. Localized 2D TOCSY imaging is shown for the first time in this work. Excitation with adiabatic GOIA-W(16,4) pulses (Gradient Offset Independent Adiabaticity Wurst modulation) provides minimal chemical shift displacement error, reduced lipid contamination from subcutaneous fat, uniform optimal flip angles, and efficient mixing for coupled spins, while enabling short repetition times due to low power requirements. Constant-density spiral readout trajectories are used to acquire simultaneously two spatial dimensions and f(2) frequency dimension in (k(x),k(y),t(2)) space in order to speed up data collection, while f(1) frequency dimension is encoded by consecutive time increments of t(1) in (k(x),k(y),t(1),t(2)) space. The efficient spiral sampling of the k-space enables the acquisition of a single-slice 2D COSY dataset with an 8 × 8 matrix in 8:32 min on 3 T clinical scanners, which makes it feasible for in vivo studies on human subjects. Here we present the first results obtained on phantoms, human volunteers and patients with brain tumors. The patient data obtained by us represent the first clinical demonstration of a feasible and robust multivoxel 2D COSY. Compared to the 2D J-resolved method, 2D COSY and TOCSY provide increased spectral dispersion which scales up with increasing main magnetic field strength and may have improved ability to unambiguously identify overlapping metabolites. It is expected that the new developments presented in this work will facilitate in vivo application of 2D chemical shift correlation MRS in basic science and clinical studies.
在这项工作中，我们引入了相关化学位移成像（CCSI）的概念。在临床扫描仪上演示了新颖的 CCSI 脉冲序列，用于二维相关光谱（COSY）和全相关光谱（TOCSY）成像实验。迄今为止，在可行且稳健的多维 2D COSY 方面的进展有限。在这项工作中首次显示了局部化的 2D TOCSY 成像。使用绝热 GOIA-W(16,4)脉冲（梯度偏移独立绝热性 Wurst 调制）进行激发可最大程度地减少化学位移位移误差，减少来自皮下脂肪的脂质污染，具有均匀的最佳翻转角，并为偶联自旋提供高效混合，同时由于功率要求低而允许短重复时间。使用恒密度螺旋读出轨迹在（k(x),k(y),t(2))空间中同时获取两个空间维度和 f(2)频率维度，以加快数据采集速度，而 f(1)频率维度则通过在（k(x),k(y),t(1),t(2))空间中连续的 t(1)时间增量进行编码。k 空间的高效螺旋采样使我们能够在 3T 临床扫描仪上以 8:32 分钟的时间采集单个切片 2D COSY 数据集，该数据集具有 8×8 矩阵，这使其能够在人体研究中进行。在这里，我们首先在体模，志愿者和脑肿瘤患者中获得了结果。我们获得的患者数据代表了可行且稳健的多维 2D COSY 的首次临床证明。与 2D J 分辨方法相比，2D COSY 和 TOCSY 提供了更高的光谱色散，其随主磁场强度的增加而增加，并且可能具有更好的能力来明确识别重叠代谢物。预计，这项工作中提出的新发展将促进 2D 化学位移相关 MRS 在基础科学和临床研究中的体内应用。
