Diradical nitroxyl spin label contrast agents for magnetic resonance imaging a comparison of relaxation effectiveness

Richard L. Ehman, Robert C. Brasch, Michael T. McNamara, Ulf Erikkson, G. Sosnovsky, J. Lukszo, S. W. Li

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The proton relaxation enhancement characteristics of seven potential MRI contrast agents containing two nitroxyl spin labels per molecule (diradicals) were compared with eight similar agents with only one spin label per molecule (monoradicals). Diradical nitroxyls were evaluated to test the hypothesis that multiple paramagnetic centers in one molecule will result in stronger proton relaxation enhancement characteristics, allowing effective contrast enhancement at lower molar concentrations and thus a reduced osmotic load and greater safety. The acute toxicity of these agents is believed to be largely related to osmotic load. Five of seven diradical nitroxyls tested had spin-lattice relaxivities that were substantially greater than all eight of the monoradicals tested. The spin-spin relaxation properties of these agents and other pertinent characteristics are favorable for contrast enhancement. The results indicate that diradical nitroxyl spin labels may be used advantageously for the design of safer, more effective MRI contrast agents.

Original languageEnglish (US)
Pages (from-to)125-131
Number of pages7
JournalInvestigative radiology
Issue number2
StatePublished - Feb 1986



  • MRI contrast agents
  • Nitroxyl spin labels
  • Proton relaxation enhancement

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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