MODIFICATION OF A WHOLE-BODY NMR IMAGER INTO A RADIO-FREQUENCY EPR SPECTROMETER SUITABLE FOR IN-VIVO MEASUREMENTS

We report the modification of a low-field whole-body NMR imager to all ow radio frequency EPR spectroscopy. The instrument is designed to giv e optimum sensitivity for in vivo detection of free radicals. The RF c ircuit is able to operate over a wide frequency range (240-320 MHz) an d is designed to handle input power levels of up to 12.5 W. The EPR re sonator is of the loop-gap type suitable for samples up to 400 ml. A r emote resonator coupling method has been developed enabling convenient matching adjustment. An automatic frequency control circuit is able t o adjust for frequency deviations caused by animal motion. Where possi ble, existing imager hardware and commercially available instruments h ave been used. The instrument is controlled from a central computer vi a an IEEE 488 instrumentation bus. Here we present sensitivity measure ments obtained from a variety of large aqueous samples containing nitr oxide free radicals. We show that the instrument is suitable for the d etection of exogenous free radicals in 200 g rats.