Three-dimensional spatial EPR imaging of the rat heart.

While instrumentation capable of performing three-dimensional EPR imaging of free radicals in whole tissues and isolated organs has been developed at L-band, important questions remain regarding the resolution and image quality that can be obtained in practice using the presently available free radical labels. Therefore, studies were performed applying three-dimensional spatial EPR imaging at L-band to image the distribution of free radical labels in the isolated heart and in phantoms of similar size. With nitroxide labels the obtainable resolution is limited by the presence of hyperfine structure in the EPR absorption function that in turn limits the maximum applicable gradient. The authors observed that with the nitroxide labels, resolutions in the range of 1-2 mm are possible, while with a single line glucose char label, resolutions of 0.2 mm are obtained. With the nitroxides, images were of sufficient resolution to resolve the overall global shape of the heart and the location of the left and right ventricular cavities; however, finer structures could not be resolved. With the glucose char much finer resolution could be obtained enabling visualization of the ventricles, aortic root, and proximal coronary arteries.