Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States.
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States.
J Magn Reson. 2020 Apr;313:106715. doi: 10.1016/j.jmr.2020.106715. Epub 2020 Mar 9.
Large enhancements in nuclear magnetic resonance (NMR) signals provided by dynamic nuclear polarization (DNP) at low temperatures have the potential to enable inductively-detected H magnetic resonance imaging (MRI) with isotropic spatial resolution on the order of one micron, especially when low temperatures and DNP are combined with microcoils, three-dimensional (3D) phase encoding of image information, pulsed spin locking during NMR signal detection, and homonuclear dipolar decoupling by Lee-Goldburg (LG) irradiation or similar methods. However, the relatively slow build-up of nuclear magnetization under DNP leads to very long acquisition times for high-resolution 3D images unless the sample volume or field of view (FOV) is restricted. We have therefore developed a method for slice selection in low-temperature, DNP-enhanced MRI that limits the FOV to about 50 μm in one or more dimensions. This method uses small-amplitude phase modulation of LG irradiation in the presence of a strong magnetic field gradient to invert spin-locked H magnetization in the selected slice. Experimental results are reported, including effects of radio-frequency field inhomogeneity, variations in the amplitude of phase modulation, and shaped phase modulation.
低温下通过动态核极化（DNP）提供的核磁共振（NMR）信号的大幅增强，有可能在低场下实现各向同性空间分辨率达到一微米量级的感应检测 H 磁共振成像（MRI），尤其是当低温、DNP 与微线圈、图像信息的三维（3D）相位编码、NMR 信号检测过程中的脉冲自旋锁定，以及 Lee-Goldburg（LG）辐照或类似方法的同核偶极去耦结合使用时。然而，DNP 下核磁化强度的缓慢建立导致高分辨率 3D 图像的采集时间非常长，除非限制样品体积或视场（FOV）。因此，我们开发了一种用于低温、DNP 增强 MRI 的切片选择方法，该方法将 FOV 限制在一维或多维的约 50 μm 左右。该方法在强磁场梯度存在下使用 LG 辐照的小幅度相位调制来反转所选切片中被自旋锁定的 H 磁化强度。报告了实验结果，包括射频场不均匀性、相位调制幅度变化和相位调制的形状的影响。
