We are developing a technique for signal enhancement in water protons based on polarization transfer from electrons in a free radical solution; our ultimate goal being increased spatial resolution for magnetic resonance microscopy. The technique consists of introducing a high concentration (20mM) of a nitroxide spin label into the sample of interest and saturating the electron spin resonance line of the spin label while the sample is being imaged. Polarization transfer from the electrons to the water protons through the Overhauser effect can increase the proton signal by as much as a factor of 110, allowing greatly increased spatial resolution. We have demonstrated a signal enhancement of a factor of 40 at low field (3.3kGauss). An electron paramagnetic resonance (EPR) spectrometer has been designed and constructed for use in our 2 Tesla magnet. This consists of a solid state microwave oscillator at a frequency of 57 Ghz, a reflection bridge, a detector, a field sweep magnet and a microwave cavity. It will be one of the few systems in the world capable of performing EPR experiments at this field strength. In the near future, a microwave cavity integrated with an NMR coil for imaging will be constructed. At 2 Tesla, with an enhancement factor of 50-100, we can in principle make the highest resolution magnetic resonance imaging micrographs ever. Intended applications include tissue samples and embryos. Aditionally , we will have the ability to perform EPR and DNP experiments on MR contrast agents, allowing us to characterize them in unique ways.
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