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Sequential, co-registered fluorine and proton field-cycled Overhauser imaging at a detection field of 59 mT

In this work we show the feasibility of sequential, co-registered fluorine and proton field-cycled Overhauser imaging at a detection field of 59 mT. To this purpose we have built an RF coil assembly comprising an Alderman–Grant resonator for EPR irradiation at 127.7 MHz (evolution field of 4.5 mT) and a solenoidal coil for 19F or 1H MRI acquisition at the detection field of 59 mT. A removable tuning/matching circuit that allows the solenoid to be tuned to the 19F frequency (2.346 MHz, FEDRI) or the 1H frequency (2.494 MHz, PEDRI) without removing the sample was built and tested. Switching of the solenoid between the 19F and 1H frequency is thus achieved in less than 1 min. The co-registered FC-FEDRI and FC-PEDRI images show higher enhancement in the sample regions with higher free radical concentration. This work is the first methodological step towards the development of an MRI scanner capable of acquiring morphological (1H) and physiological (19F) images in animal models at very low fields.