One- and two-dimensional EPR imaging studies on phantoms and plant specimens.

The advantages of electron paramagnetic resonance (EPR) imaging at L-band frequencies are discussed. The construction and calibration of a low-field L-band EPR imaging spectrometer is described with capillary phantoms containing aqueous nitroxides as paramagnetic imaging agents. The peak separation induced by the magnetic field gradient is related to the object separation. The linewidth of each (first-derivative) line is used to calculate the dimensions of each paramagnetic object, which is the sum of an intrinsic and a gradient-induced component. By extrapolating the linewidth back to zero field gradient, one obtains the intrinsic linewidth correction factor in computing image size. The nonuniformity caused by deterioration of biological substructure was examined with plant stems where one capillary vessel had become leaky. Spin-label destruction, particularly by biological reducing agents, was compared for three species of plant stems.