A three-coil RF probe-head at 2.35 T: Potential applications to the 23Na and to the hyperpolarized 129Xe MRI in small animals

We present in this paper a dedicated home-built RF probe-head for the MRI of rat brain at 2.35 T. This probe consists of an association of three coils: a double-tuned birdcage coil, which could be used for both transmitting and receiving, and a single-tuned surface coil that is used for the only receiving. This single-tuned coil is actively decoupled from the double-tuned volume coil. The active decoupling is based on the pole insertion technique using PIN diodes circuitry. This development was initially motivated by its potential and future application to the brain perfusion measurements by the MRI of hyperpolarized xenon-129 (HP ¹²⁹Xe). However, one of underlying ideas behind this work is to proceed well beyond this specific application. Particularly, the developed coil could also be dedicated for the sodium-23 (²³Na) MRI in the rat brain. Indeed we tried to make the design versatile, simple and easy to replicate by other research groups, with a low cost, minimum development time and accepted performances. We believe that this design could by useful for groups who consider building own hardware. This is why we describe in some details the practical aspects of the workbench design as well as the coil characterization. For simplicity reasons, the first results of developed prototype were obtained at 100 MHz and 26.4 MHz (proton and sodium-23 frequencies at 2.35 T). MR images of phantoms were realized. In-vivo ¹H images and ²³Na spectra of the rat brain were also obtained. Future validation would concern the MRI of HP ¹²⁹Xe.