New experimental procedures for in vivo L-band and radio-frequency EPR spectroscopy/imaging

Electron paramagnetic resonance spectroscopy/imaging experiments are currently being performed on small animals and isolated organs. The exogenous paramagnetic probes commonly used are nitroxide (aminoxyl) free radicals. Nitroxide reduction and clearance were evaluated to understand in vivo distribution and metabolism. Pharmacokinetics data were collected with the same nitroxide at three different frequencies in an external rat blood circuit, in a mouse head and in a whole rat body. A 280 MHz spectrometer made it possible to obtain images of a whole rat body after nitroxide intravenous injection. At L-band (1500 MHz), a synchronization technique was used to obtain images of a dynamic phantom utilized to mimic the model of the isolated perfused rat heart. Different experimental procedures are discussed and the problems which affect sensitivity and resolution are evaluated.