ABSTRACT
This chapter provides some general comments about electron paramagnetic resonance (EPR) imaging, a comparison with nuclear magnetic resonance (NMR) imaging, and a discussion of various approaches to EPR imaging. There are several important differences between EPR and NMR imaging. NMR imaging was based initially on proton resonances that are in high abundance in many samples, whereas EPR imaging examines unpaired electrons that typically are present in relatively low abundance. Dielectric loss is greater at the microwave frequencies used in EPR than at the radio-frequencies used in NMR. The first EPR-imaging experiments emphasized spatial coordinates and maps of electron spin density. Pulsed EPR imaging has been performed with both continuous wave and pulsed gradients and field-swept echo-detected EPR. The simplest EPR-imaging experiment examines a sample with a single paramagnetic species with no hyperfine splitting and a constant linewidth. In principle, EPR imaging can be applied to any sample with a nonuniform distribution of unpaired electrons.
