1. Contribution from the Biomedical Magnetic Resonance Laboratory, Department of Medical Information Sciences, College of Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, Beckman Institute, 405 N. Mathews, Urbana, Illinois 61801, Department of Chemistry and Department of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61821, Cornell Theory Center, Cornell University, Ithaca, New York 14853, and National Cancer Institute, National Institutes of...