University of Virginia
For over two decades, polarized He-3 has proven to be a powerful tool for investigating the structure of the neutron. The advent of liter-scale polarized He-3 targets, in turn, led quickly to magnetic resonance imaging of the gas space of human lungs with unprecedented resolution. Clinical research using "noble-gas imaging" quickly came to include the use of polarized Xe-129, and both gases have seen extensive use in research related to pulmonary disease and drug discovery. Because xenon dissolves readily into blood, there has also been interest in imaging other organ systems. Outside the lungs, however, results have been limited by small signals. In addition to providing some historical context, I will describe a new imaging modality that builds on noble-gas imaging, but that has enormously increased sensitivity. Spatial information is encoded using magnetic-field gradients, but imaging data are acquired entirely through the detection of gamma rays (without the use of a gamma camera). The quantity of atoms needed for producing images is reduced by more than a factor of a million, creating the potential for a new type of nuclear tracer. Indeed, so few atoms are required that novel polarization techniques can be considered as a path for expanding the range of applications.
About the speaker
Professor Gordon Cates conducts research in three diverse areas spanning atomic, nuclear, and medical physics. Unifying these activities is the use of optical pumping and spin exchange, techniques that make it possible to polarize the spins of electrons, atoms and nuclei using light sources such as lasers. Critical to such research is the study of spin interactions during atomic collisions, spin-relaxation at surfaces, and numerous aspects of laser physics.
A major thrust of Prof. Cates’ research has been understanding the “spin-structure” of the neutron. These efforts, involving electron scattering from spin-exchange polarized 3He targets at SLAC and Jefferson Laboratory (JLab), have helped shed light on the foundations of QCD and the question of what it is within the nucleon that carries spin. Prof. Cates has also been involved in studying parity violation in polarized electrons scattering in order to search for the presence of strange quarks in the nucleon (at JLab) and for physics beyond the standard model (at SLAC).
Another important aspect of Prof. Cates’ research involves a new type of MRI in which a subject inhales a laser-polarized noble gas such as 3He or 129Xe which is subsequently imaged. Coinvented by Prof. Cates in the early 1990’s, “hyperpolarized gas imaging” produces images of the gas space of the lungs of unprecedented resolution. Also, since Xe dissolves readily into the blood and various tissues in the body, there is potential to extend the technique to other organs. Many basic physics issues remain critical to the continuing development of hyperpolarized gas imaging.