Design and development of a new dedicated RF sensor for the MRI of rat brain

Abstract

The design and development of a new dual-frequency RF probe-head are presented. This probe was initially dedicated for the MRI of both proton (1H) and hyperpolarized Xenon-129 (HP 129Xe) in the rat brain at 2.35 Tesla. It consists of a double-tuned (100 MHz- 27.7 MHz) volume coil, which could be used for both transmitting and receiving, and of a receive-only single-tuned (27.7 MHz) coil. The double-tuned coil consists of two concentric birdcage resonators. The inner one is a low-pass design and it is tuned to 27.7 MHz, while the outer one, tuned to 100 MHz, is high-pass. The receive-only coil is a surface coil which is decoupled from the double-tuned volume coil by an active decoupling circuitry based on the use of PIN diodes. A home-built Transmit/Receive (T/R) driver ensures biasing of the PIN diodes in both volume and surface coils. The original concepts of the design are addressed, and practical details of realization are presented. One of the underlying ideas behind this work is to proceed well beyond the application to the MRI of HP 129Xe. Actually, this design could be easily adapted for a large palette of other MRI applications. 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. The prototype was validated at 100 MHz and at 26.4 MHz (sodium-23 resonance frequency at 2.35 T). MRI experiments were performed using phantoms. In vivo 1H images and 23Na spectra of the rat brain are also presented.