ABSTRACT
This chapter discusses some of system requirements as well as to some of the other limiting factors encountered in attempting electron paramagnetic resonance (EPR) on living systems. The challenge of developing both spin-imaging and in vivo EPR in living systems required a large number of changes in classical, commercially available EPR apparatus. Commercial EPR spectrometers operating at X-band are very limited when using water-containing samples due to large dielectric losses. The loop-gap resonators and reentrant cavity have emerged as the most suitable resonators for in vivo EPR experiments. Iron-core magnets have been the most common magnetic-field sources in commercial X-band EPR spectrometers. For L band and lower-frequency EPR imaging, it might be safer and more accurate to coalign the field gradient with applied field direction and rotate the sample. The lower frequencies required for 8in vivo EPR spectroscopy experiments also dictated several changes in microwave-bridge construction.
