Nuclear magnetic resonance (NMR) is a powerful tool for applications in analytical chemistry, materials science, and the screening of compounds in search for new medications. Magnetic resonance imaging (MRI), an offshoot of NMR, capitalizes on the same scientific principles study structures inside the human body, providing a critically important tool for diagnostic and cognitive (neurological) biomedical imaging. A major drawback of both NMR and MRI is the need for large, immobile, and costly superconducting magnets and associated infrastructure. With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, and co-funding from the Molecular Biophysics Program in the Division of Molecular and Cellular Biosciences, Professors Alex Pines and Dmitry Budker and their groups at the University of California - Berkeley, seek to provide new methodology that enables magnetic resonance data to be obtained without the need for the huge magnets and with simple infrastructure, thereby producing information and images with equipment that is compact, mobile and less costly by a factor of 10-100. The research offers significant impact on technical innovation from chemistry to biomedicine, while contributing to the training of an advanced workforce.
The purpose of the high magnetic field, Bo, in traditional NMR and MRI is twofold: a) to act as a means of polarizing the nuclear spins and b) for the efficient inductive detection of the magnetization precession. Each is proportional to the magnitude of the field so the total detected signal is proportional to the square of that field. This accounts for the advantage of high fields (and their corresponding high frequencies) for spectroscopy and imaging. Typical magnetic fields for current commercial NMR instrumentation range from 10-25 Tesla. In order to dispense with the high field, alternative means of polarization and detection are required. Polarization can be accomplished by optical pumping and/or parahydrogen-induced polarization. Both methods produce "hyperpolarization" at zero to ultralow fields (ZULF) which is in fact several orders of magnitude greater than the thermal spin polarization at high field. For detection, a non-inductive quantum detector is required. Previous research utilized the high sensitivity of a superconducting quantum interference device (SQUID) that operates at liquid helium temperature. Professors Pines and Budker are now employing a laser atomic magnetometer that can also detect ultralow precession with high sensitivity but at room temperature. To date, they have produced ZULF spectra with high signal/noise and with line widths of the order of 10mHz. In this project, they are expanding the methodology to include: 1) sophisticated ZULF pulse sequences for spin decoupling; 2) approaches to selective excitation of single transitions; 3) two-dimensional spectroscopy for atomic spin interactions; 4) separation of spin isotopomers; and 5) quantum correlations. The spectra and information emanating from this work may enhance the applicability of NMR spectroscopy in analytical chemistry and chemical biology.
