Quadratic Echoes and the MRI of Hard and Soft Solids

从历史上看，“观察”不透明固体内部的新工具的开发一直是科学技术进步的重要推动力，具有深远的经济影响。该项目正在开发新的方法，以实现磁共振成像（MRI）领域的一个长期目标，即高空间分辨率的硬和软固体的多核磁共振图像。传统的核磁共振成像只能检测液态水中氢的信号；固体的核磁共振成像非常困难，很少有人尝试。为了对固体进行高分辨率磁共振成像，该项目使用了二次回波线缩小的创新技术，这是NSF在好奇心驱动的基础研究上投资的直接结果。潜在的固体目标包括多孔岩石、复合材料、3D集成电路中的“硅通孔”、骨骼和软组织。前沿科学具有广泛的潜在应用前景，可以为从本科早期到博士阶段的学生提供优秀的教育和培训，以及K-12的推广工作。虽然该项目的工作计划旨在做出基础科学贡献，但这项工作应该在其他科学技术领域找到应用，并且也有潜在的社会效益。例如，将一种全新的实验工具应用于颗粒物理问题，如筒仓中谷物的特性，可以在一个对工业非常重要的领域推进理论和实验。技术摘要：硬脉冲和它们的δ函数近似之间的微小差异可以用来产生新的自旋回波，这些自旋回波在核磁共振（NMR）、磁共振成像（MRI）或固体显微镜以及相关光谱学中有很好的应用前景。例如，利用二次回波线窄化脉冲序列，一种控制自旋相干性的新工具，本项目正在寻求一种新的方法来进行高空间分辨率的固体MRI。该项目非常注重从本科早期到博士阶段的学生的教育和培训，以及K-12的推广工作。虽然这项工作计划旨在做出基础科学贡献，但也有潜在的社会效益。首先，推进新形式的自旋相干控制，适用于各种自旋（伪自旋，或量子位）哈密顿量，在光谱学的许多领域都很有用。作为这项工作的一部分，我们正在努力将二次回波的范围扩展到更大范围的原子核（例如，碳-13，硅-29）和实验系统。其次，寻找从更少的数据中挤出更多信息的方法，以努力加速固体成像，这对用于生物学和化学（包括药物发现）结构确定的核磁共振有直接的好处。该项目基于Veit Elser的迭代地图方法，从非均匀采样数据中重建高质量的MR图像（或NMR波谱），这是一种非常适合该应用的压缩感知形式。第三，将一种全新的实验工具应用于颗粒物理问题，将在一个对工业非常重要的领域推进理论和实验。从历史上看，我们“看到”不透明固体内部的能力的提高产生了更广泛的影响。

Non-technical AbstractHistorically, the development of new tools to 'see' inside opaque solids has been an important driver of progress in science and technology, with far-reaching economic impact. This project is developing new approaches to a long-standing goal in the field of magnetic resonance imaging (MRI), namely, multinuclear MR images of hard and soft solids with high spatial resolution. Conventional MRI detects only the signal from the Hydrogen in liquid water; MRI of solids is so much more difficult that it is rarely attempted. To perform high-resolution MR imaging of solids, this project uses the innovation of quadratic echo line-narrowing, which was recently discovered as a direct result of the NSF's investment in basic, curiosity-driven research. Potential solid targets include porous rocks, composite materials, "through-silicon vias" in 3D integrated circuits, bone and soft tissues. Cutting-edge science with a broad range of potential applications enables excellent education and training of students from the early undergraduate level through the Ph.D., along with K-12 outreach efforts. While this project's plan of work is aimed at making fundamental scientific contributions, the work should find applications in other areas of science and technology, and there are potential societal benefits as well. For example, applying an entirely new experimental tool to problems in granular physics, such as the properties of grain in silos, can advance theory and experiment in a field that is very important to industry.Technical AbstractThe small difference between hard pi-pulses and their delta-function approximation can be used to generate new classes of spin echoes which have promising applications in nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI) or microscopy of solids, and related spectroscopies. For example, using the quadratic echo line-narrowing pulse sequence, a novel tool for the control of spin coherence, this project is pursuing a new approach to carrying out MRI of solids with high spatial resolution. This project has a strong focus on the education and training of students from the early undergraduate level through the Ph.D., along with K-12 outreach efforts. While the plan of work is aimed at making fundamental scientific contributions, there are potential societal benefits as well. First, advancing new forms of spin coherence control, applicable to a wide variety of spin (pseudospin, or qubit) Hamiltonians, is broadly useful in many areas of spectroscopy. As part of this effort, we are working to extend the reach of quadratic echoes to an even wider range of nuclei (e.g., Carbon-13, Silicon-29) and experimental systems. Second, finding ways to squeeze more information from less data, in an effort to accelerate the imaging of solids, has immediate benefits to the kind of NMR that is used for structure determination in biology and chemistry (including drug discovery). This project's efforts to reconstruct high-quality MR images (or NMR spectra) from non-uniformly sampled data build upon Veit Elser's iterated maps approach, which is a form of compressed sensing well-suited for this application. Third, applying an entirely new experimental tool to problems in granular physics will advance theory and experiment in a field that is very important to industry. Historically, improvements in our ability to 'see' inside opaque solids have had broader impacts.