A dual-frequency circularly polarizing whole-body MR antenna for 69/170 MHz

The design concept of a dual-frequency whole-body MR antenna for circular polarization is presented. First, the principle of the capacitively shortened transmission line antenna, which is the basis of the design, is discussed. Emphasis is given to the antenna design at high frequencies. Two variants of possible antenna constructions are described and the RF efficiency is calculated for both frequencies. The antenna performance is discussed for the example of 69 and 170 MHz, the nuclear magnetic resonance frequencies of the nuclei 31P and 1H at 4 T. For 31P experiments, a whole-body antenna is useful only for transmitting and, thus, the antenna performance can be optimized for 1H. The design principle is not limited to two frequencies; however, the RF efficiency decreases with an increasing number of resonance frequencies. Results of a laboratory version and 1H images at 4 T are presented.