Oxygen imaging in perfused hearts by dynamic nuclear polarization.
The feasibility of localized oximetry by dynamic nuclear polarization (DNP) imaging is demonstrated on perfused sheep hearts. DNPI is a magnetic, double resonance technique, in which the electron paramagnetic resonance (EPR) of a free radical dissolved in a perfusion medium is saturated, while the nuclear magnetic resonance (NMR) of water protons is used to perform conventional NMR imaging. The presence of oxygen reduces the enhancement of the NMR signal induced by DNP. The oxygen content of sheep heart tissues was detected by the subtraction of the DNP image of the heart, perfused with a nitrogen-equilibrated solution, from an image obtained when the heart was perfused with an oxygen-equilibrated solution. This result was obtained with extreme oxygen partial pressure, and the discussion presents physical and chemical means for improving the DNP imaging method. Physical means include field cycling, electron paramagnetic rotary saturation, and the use of a 180 degrees NMR pulse before EPR irradiation. The chemical means discussed are deuterium substitution in nitroxides and the potential use of solid, free radical probes. It is suggested to use the perfused heart model for comparing the numerous methods available to measure the oxygen content of tissues.
Institut de Physique Biologique URA 1173 du CNRS, Strasbourg, France.
D
D
Grucker
J
J
Chambron
D000818:Animals; D003331:Coronary Vessels; D004578:Electron Spin Resonance Spectroscopy; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy; D010100:Oxygen / Q000097:blood*; D012756:Sheep
D010100:Oxygen