Localized T1 measurements using an inversion-recovery OSIRIS method

Oximetry by dynamic nuclear polarization

This study describes quantitatively the effect of O2 on the dynamic nuclear polarization (DNP) of water protons. It is shown theoretically how DNP enhancement is altered by the paramagnetism of O2. The nonlinear effect of oxygen on the enhancement factor has been approximated by a first order expression that provides accurate predictions of the experimental results obtained with phosphate-buffered solutions of 2,2,6,6 tetramethyl-4-oxo-piperidine-N-oxyl. The proton relaxation rates and DNP line width were measured for nitroxide concentrations ranging from 0.5 to 10 mM and for oxygen partial pressures ranging from 0 to 760 mmHg. A method is suggested for the calculation of the nitroxide and oxygen concentrations of a sample, based on two measurements, one with on-resonance EPR irradiation, the other with slightly off-resonance irradiation. Although the correlation between the values for the actual and calculated oxygen concentrations is good, the accuracy of the calculated oxygen concentration values remains poor, because of the large number of parameters involved in this calculation.

Localized T2 measurements using an OSIRIS-CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect

This work presents a new method allowing localized T2 measurements, based upon the OSIRIS scheme. A train of 180 degrees pulses is applied after the OSIRIS preparation cycle, recording directly the transverse magnetization decay. The method was verified for two nuclei, 1H and 19F, with phantoms and in vivo on rats. The accuracy of the T2 values is discussed, as well as possible applications of the OSIRIS-CPMG method to proton transverse spin relaxation measurements, free of diffusion effects, and to non-invasive in vivo blood oxygenation measurements, through the use of an emulsion of perfluorooctylbromide, a blood substitute containing fluorine.