Quadratic Echoes and the MRI of Hard and Soft Solids

Yale University, New Haven CT

Investigators

Abstract

Non-technical Abstract Historically, 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 Abstract The 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.