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Contrast Agents and Spectroscopic Probes in NMR

Dana Farber Cancer Institute, Massachusetts General Hospital, and Harvard Medical School, Boston, Massachusetts

Correspondence: For reprints contact: Jason A. Koutcher, MD, Phd, NMR Office, Research 501, Mass. General Hospital, Boston, MA 02114.

ABSTRACT

The demand for higher diagnostic specificity has led to the increased use of "foreign" agents to increase tissue contrast and/or spectroscopic sensitivity in NMR studies. The primary agents used to enhance tissue contrast in NMR imaging are paramagnetic. They cause a decrease in the proton T₁ of H₂O, leading to enhanced signal intensity. This effect depents on the large gyromagnetic ratio of the electron, the number of unpaired electrons, the concentration of paramagnetic ions, the number of coordinated water molecules, and the rate of exchange of water. Spectroscopic enhancement has relied primarily on attempts at isotopic enrichment (usually C-13), which causes a direct increase in signal.