Solid-state NMR, Leiden Institute of Chemistry, Faculty of Science, Leiden University;
Laboratory of Biophysics, Wageningen University & Research; Laboratory of BioNanoTechnology, Wageningen University & Research; MAGNEtic resonance Facility, Wageningen University & Research.
J Vis Exp. 2021 Jan 16(167). doi: 10.3791/61266.
This protocol describes a signal-to-noise ratio (SNR) calibration and sample preparation method for solenoidal microcoils combined with biological samples, designed for high-resolution magnetic resonance imaging (MRI), also referred to as MR microscopy (MRM). It may be used at pre-clinical MRI spectrometers, demonstrated on Medicago truncatula root samples. Microcoils increase sensitivity by matching the size of the RF resonator to the size of the sample of interest, thereby enabling higher image resolutions in a given data acquisition time. Due to the relatively simple design, solenoidal microcoils are straightforward and cheap to construct and can be easily adapted to the sample requirements. Systematically, we explain how to calibrate new or home-built microcoils, using a reference solution. The calibration steps include: pulse power determination using a nutation curve; estimation of RF-field homogeneity; and calculating a volume-normalized signal-to-noise ratio (SNR) using standard pulse sequences. Important steps in sample preparation for small biological samples are discussed, as well as possible mitigating factors such as magnetic susceptibility differences. The applications of an optimized solenoid coil are demonstrated by high-resolution (13 x 13 x 13 μm, 2.2 pL) 3D imaging of a root sample.
本协议描述了一种结合生物样本的螺线管微线圈的信噪比（SNR）校准和样品制备方法，专为高分辨率磁共振成像（MRI）设计，也称为磁共振显微镜（MRM）。它可用于临床前 MRI 光谱仪，在 Medicago truncatula 根样本上进行了演示。微线圈通过将 RF 谐振器的大小与感兴趣的样本大小相匹配来提高灵敏度，从而在给定的数据采集时间内实现更高的图像分辨率。由于设计相对简单，螺线管微线圈易于构建且价格低廉，并且可以轻松适应样品要求。系统地，我们解释了如何使用参考溶液校准新的或自制的微线圈。校准步骤包括：使用偏转角曲线确定脉冲功率；估计 RF 场均匀性；以及使用标准脉冲序列计算体积归一化信噪比（SNR）。讨论了小生物样本样品制备的重要步骤，以及诸如磁导率差异等可能的缓解因素。通过对根样本进行高分辨率（13 x 13 x 13 μm，2.2 pL）3D 成像，展示了优化的螺线管线圈的应用。
