New experimental apparatus for multimodal resonance imaging: initial EPRI andNMRI experimental results

Abstract

Electron paramagnetic resonance imaging (EPRI) is a recentlydeveloped imaging technique employed in the study of free radicals in livingsystems. A full understanding of many physiological and pathological processesinvolving free radicals has not yet been attempted. The reason for this isthat whilst nuclear magnetic resonance imaging (NMRI) is able to generate veryaccurate images of soft tissues and organs, EPRI does not have this capabilitybecause of its sensitivity limitations and the large linewidths ofparamagnetic probes.This work describes the development and optimization of a multimodal apparatuscapable of performing both pulsed EPRI and NMRI experiments on the samesample. The instrument combines the possibilities offered by both techniques:the functional and biochemical information achieved with EPRI, and thehigh-resolution anatomical images generated by NMRI. At present, theseexperiments are performed by moving the sample from an EPRI spectrometer to anNMRI apparatus. Consequently, the acquisition times are very long and severalproblems arise in image reconstruction. On the other hand, a unique apparatusoperating in the two modalities greatly reduces the acquisition times andmakes it possible to relate accurately the observed distribution of electronspin density with the anatomical description of individual organs.The experiments are performed at 357 Gauss, corresponding to a resonance frequencyof 1.52 MHz for NMR and 1 GHz for EPR. In the present work, a detaileddescription of the apparatus is reported, including the main magnet, thegradient assembly, the multimodal cavity and the transmitter and receiversystems. The preliminary experimental results obtained by this apparatus arepresented.