Simultaneous multi-site EPR spectroscopy in vivo.

A gradient technique to measure electron paramagnetic resonance spectra simultaneously at several different locations is described. The technique is based on the use of point probes containing paramagnetic centers. The value of the magnetic field gradient is chosen to be sufficient to separate the EPR signals from the different paramagnetic probes yet at the same time small enough to change only minimally the shape of individual signals. The conditions to apply this technique are considered in detail. When experimental data have a high signal-to-noise ratio, the lineshape distortion induced by the gradient can be corrected with the aid of a known distribution function of paramagnetic centers within the probe. The maximum entropy deconvolution algorithm is successfully applied for the correction of significantly distorted lines. The technique is experimentally tested and applied to measure the concentration of oxygen in hypertrophied rat myocardium and normal rat kidney in vivo by low frequency EPR (L-band, 1.2 GHz). Two types of EPR oxygen-sensitive probes--lithium phthalocyanine crystals and synthetic carbohydrate chars--were used.