A composite resonator for simultaneous NMR and EPR imagingexperiments

Abstract

Electron paramagnetic resonance imaging (EPRI) and nuclear magneticresonance imaging (NMRI) are currently used for in vivo spectroscopyand imaging. A multimodal apparatus based on the simultaneous observation ofelectronic and nuclear signals is very desirable because it combines theability of NMRI to provide an accurate description of the internal structureof a sample with the ability of EPRI to detect the presence of free radicalsand map their distribution. At a given value of the magnetic field B0, the electronic and nuclear transitions have very different resonancefrequencies. This required the development of a multimodal spectrometer thatcombined the two spectroscopic modalities. In spite of the complexity of theelectronic apparatus involved, the main requirement was for a resonator thatallowed the simultaneous irradiation and observation of the signals at the twofrequencies with good sensitivity. The EPR section of the composite resonatorconsists of a one-loop, two-gap resonator tuned to 1 GHz and the NMR sectionis a solenoid, coaxial to the EPR section, tuned to 1.52 MHz. Both sectionshave been designed to produce a homogeneous rf field in a cylindrical regionof diameter 3 cm and length 4 cm. The rf magnetic fields B1e and B1nare directed along the axis of the magnet. The probe was tested on a phantomcomprising two separate regions containing 0.73 g of lithium phthalocyanine(LiPtc) powder and 20 ml of an aqueous solution of CuSO4, respectively, andboth EPR and NMR signals have been collected. Measurements of the sensitivityhave also been made.