Electron paramagnetic resonance imaging of the rat heart.

It has been hypothesized that free radical metabolism, oxygenation and nitric oxide generation in biological organs such as the heart may vary over the spatially defined tissue structure. To address fundamental questions regarding the role of spatially localized alterations in radical metabolism, oxygenation and nitric oxide in the pathophysiology of cellular injury during ischaemia, we have developed instrumentation optimized for 3D spatial and 3D or 4D spectral-spatial imaging of free radicals in the isolated perfused rat heart at 1.2 GHz. Using this instrumentation, high-quality 3D spectral-spatial imaging of nitroxide metabolism was performed as well as spatially localized measurements of oxygen concentrations, based on the oxygen-dependent linewidth broadening observed. In these spectral-spatial images, submillimetre resolution was observed enabling visualization of the left ventricular and right ventricular myocardium. With 3D spatial imaging using single-line labels, resolutions down to 100 to 200 microm were obtained enabling visualization of the ventricles, aortic root and proximal coronary arteries. Using metal complexes which trap nitric oxide, measurement and imaging of nitric oxide generation during ischaemia was performed. With the use of 15N isotope labelling it was possible to map the metabolic pathway of this nitric oxide generation. Thus, EPR imaging is a powerful tool which can provide unique information regarding the spatial localization of free radicals, oxygen and nitric oxide in biological organs and tissues.