New experimental apparatus for multimodal resonance imaging: initial EPRI and NMRI experimental results

Electron paramagnetic resonance imaging (EPRI) is a recently developed imaging technique employed in the study of free radicals in living systems. A full understanding of many physiological and pathological processes involving free radicals has not yet been attempted. The reason for this is that whilst nuclear magnetic resonance imaging (NMRI) is able to generate very accurate images of soft tissues and organs, EPRI does not have this capability because of its sensitivity limitations and the large linewidths of paramagnetic probes. This work describes the development and optimization of a multimodal apparatus capable of performing both pulsed EPRI and NMRI experiments on the same sample. The instrument combines the possibilities offered by both techniques: the functional and biochemical information achieved with EPRI, and the high-resolution anatomical images generated by NMRI. At present, these experiments are performed by moving the sample from an EPRI spectrometer to an NMRI apparatus. Consequently, the acquisition times are very long and several problems arise in image reconstruction. On the other hand, a unique apparatus operating in the two modalities greatly reduces the acquisition times and makes it possible to relate accurately the observed distribution of electron spin density with the anatomical description of individual organs. The experiments are performed at 357 Gauss, corresponding to a resonance frequency of 1.52 MHz for NMR and 1 GHz for EPR. In the present work, a detailed description of the apparatus is reported, including the main magnet, the gradient assembly, the multimodal cavity and the transmitter and receiver systems. The preliminary experimental results obtained by this apparatus are presented.