Electron paramagnetic resonance (EPR) spectroscopy is dedicated to the research of substances with unpaired electrons. It was first introduced in 1944, approximately the same time as the similar phenomenon - nuclear magnetic resonance (NMR).Zavoisky E. Spin-magnetic resonance in paramagnetics. J Phys Acad Sci USSR. 1945;9:211–45.Purcell E, Torrey H, Pound R. Resonance absorption by nuclear magnetic moments in a solid. Phys Rev. 1946;69:37–338. Owing to hardware and software limitations, EPR was not developing as rapidly as NMR. This led to a huge gap between these two methods. Therefore, to underline a breakthrough in preclinical imaging, by presenting EPRI as a complementary method to the present ones, the term "ERI" was introduced.
