A composite resonator for simultaneous NMR and EPR imaging experiments

Electron paramagnetic resonance imaging (EPRI) and nuclear magnetic resonan ce imaging (NMRI) are currently used for in vivo spectroscopy and imaging. A multimodal apparatus based on the simultaneous observation of electronic and nuclear signals is very desirable because it combines the ability of NM RI to provide an accurate description of the internal structure of a sample with the ability of EPRI to detect the presence of free radicals and map t heir distribution. At a given value of the magnetic field B-0, the electron ic and nuclear transitions have very different resonance frequencies. This required the development of a multimodal spectrometer that combined the two spectroscopic modalities. In spite of the complexity of the electronic app aratus involved, the main requirement was for a resonator that allowed the simultaneous irradiation and observation of the signals at the two frequenc ies with good sensitivity. The EPR section of the composite resonator consi sts of a one-loop, two-gap resonator tuned to 1 GHz and the NMR section is a solenoid, coaxial to the EPR section, tuned to 1.52 MHz. Both sections ha ve been designed to produce a homogeneous rf field in a cylindrical region of diameter 3 cm and length 4 cm. The rf magnetic fields B-1e and B-1n are directed along the axis of the magnet. The probe was tested on a phantom co mprising two separate regions containing 0.73 g of lithium phthalocyanine ( LiPtc) powder and 20 ml of an aqueous solution Of CuSO4, respectively, and both EPR and NMR signals have been collected. Measurements of the sensitivi ty have also been made.